THESlS _ II III I IIIIIIII‘IIIIIIIIIIIIIIIII"? I"”'” “I 3 1293 19741 5790- ; ’ This is to certify that the thesis entitled HERBICIDAL ACTIVITY OF ETHALFLURALtN AND ITS UPTAKE AND TRANSLOCATION IN SELECTED VEGETABLE caops presented by MICHAEL DEAN WILLIS has been accepted towards fulfillment of the requirements for PH.D. degreein HORTICULTURE Mwflw Major professor Alan Putnam Date Guam-J II: I283 0-7639 MS U is an Affirmative Action/Equal Opportunity Institution MSU RETURNING MATERIALS: Place in book drop to LJBRAfiJES remove this checkout from .“ your record. FINES will be charged if book is returned after the date stamped below. J' vkx HERBICIDAL ACTIVITY OF ETHALFLURALIN AND ITS UPTAKE AND TRANSLOCATION IN SELECTED VEGETABLE CROPS By Michael Dean Willis A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Horticulture 1983 ABSTRACT HERBICIDAL ACTIVITY OF ETHALFLURALIN AND ITS UPTAKE AND TRANSLOCATION IN SELECTED VEGETABLE CROPS by Michael Dean Willis This study examined differential selectivity of ethalfluralin [N- ethyl-N-(2-methyl-2-propenyl)-2,6-dinitro-4-(trif1uoromethy1) benzena- mine], among cucurbit species and among bean (Phaseolus vulgaris L.) and cucumber (Cucumis sativus L.) cultivars. The fate of ethalfluralin was also determined in beans, cucumbers and peas (Pisum sativum L.). In field sudies, preemergence (PRE) applications at 1.12 or 1.68 kg/ha provided excellent control of several broadleaved and grass weed species. Clear plastic mulch increased growth of transplanted muskmel- ons (Cucumis melo L.) compared to no mulch, and improved crop tolerance to ethalfluralin applied at 1.68 kg/ha preplant incorporated. Adequate crop tolerance was observed on direct seeded muskmelon as well as sever- al cultivars of squash and pumpkin (Cucurbita sp.) after PRE applica- tions of 1.12 to 1.68 kg/ha. Injurious concentrations of ethalfluralin caused gross radial en- largement of bean root tips, swelling of hypocotyls and inhibition of hypocotyl unhooking. Inhibition of lateral root development, restric- Michael Dean Willis tion of hypocotyl elongation and hypocotyl swelling were observed in cu- cumbers. 'Spartan Arrow', a green bush bean, was the most sensitive of seven bean cultivars tested while 'Domino', a black turtle type bean, exhibited excellent tolerance to 9 kg/ha ethalfluralin. 'GP14A' and 'Tempo' cucumbers were most tolerant to preplant incorporated ethalflur- alin at 1.12 kg/ha while 'Marketmore 70', 'Marketmore 76' and 'Calypso' were the most susceptible of 54 cultivars tested. In field and greenhouse studies significantly more 14C accumulated in leaves of cucumbers than in petioles, stems or fruits after root exposure to 14C-ethalfluralin. Cucumber fruit from plants treated with 14 1.68 kg/ha PRE contained 0.017 ppm C-residue while bean and pea seeds from plants treated at 1.68 kg/ha preplant incorporated contained 0.053 14 ppm and 0.142 ppm C-residue respectively. 14C labeled material was observed in both cucumber cotyledons and bean leaf tissue 2 h after root 14 exposure to 14C-ethalfluralin. Absorption of C-ethalfluralin vapor was observed in both cucumber cotyledon and stem tissue. Both cucumber 14C-ethalfluralin topically applied to the stem and and bean absorbed readily translocated the 14C acropetally, while only limited basipital translocation occurred. ACKNOWLEDGEMENTS The author wishes to gratefully thank Dr. A.R. Putnam for the opportunity to pursue a dream and the invaluable experience gained under his direction. The assistance of Dr. Karen Baker in conducting much of the microautoradiography work is acknow- ledged. The assistance of Mr. W. Chase and my fellow students in conducting these studies was invaluable. I would like to thank Dr. S. Ries, Dr. W. Meggitt, Dr. D. Penner and Dr. H. Price for their time and effort in reviewing and critiqueing this dissertation. A special thanks is extended to Dr. T. Golab for his technical assistance and to Lilly Research Laboratories for supplying 14C-ethalfluralin and financial support. The support obtained from the author's family made it all possible. ii TABLE OF CONTENTS Page INTRODUCTION ..................................................... 1 CHAPTER 1 - DINITROANILINE HERBICIDES - A LITERATURE REVIEW ...... 3 HISTORY ..................................................... 3 PHYSICAL AND CHEMICAL PROPERTIES ............................ 4 FATE IN PLANTS .............................................. 4 UPTAKE AND TRANSLOCATION ............................... 4 METABOLISM ............................................. 8 PLANT RESPONSES ........................................ 11 FATE IN SOILS ............................................... 12 VOLATILITY ............................................. 12 PHOTODEGRADATION ....................................... 14 SOIL MOVEMENT .......................................... 14 ADSORPTION ............................................. 15 MICROBIAL/CHEMICAL DEGRADATION ......................... 15 LITERATURE CITED ............................................ 17 CHAPTER 2 - RESPONSE OF SELECTED CUCURBIT CROPS AND ANNUAL NEED SPECIES TO SOIL APPLICATIONS OF ETHALFLURALIN...22 ABSTRACT .................................................... 22 INTRODUCTION ................................................ 24 METHODS AND MATERIALS ....................................... 26 MUSKMELON STUDIES ...................................... 26 Page CUCUMBER STUDIES ....................................... 28 WATERMELON STUDY ........................................ 28 SUMMER SQUASH STUDY .................................... 29 WINTER SQUASH STUDIES .................................. 29 PUMPKIN STUDY .......................................... 29 RESULTS AND DISCUSSION ...................................... 29 MUSKMELON STUDIES ...................................... 29 CUCUMBER STUDIES ....................................... 35 WATERMELON STUDY ....................................... 42 SUMMER SQUASH STUDY .................................... 42 WINTER SQUASH STUDY .................................... 42 PUMPKIN STUDY .......................................... 42 LITERATURE CITED .......................... ' .................. 48 CHAPTER 3 - RESPONSE OF SELECTED CULTIVARS OF BEANS (Phaseolus vulgaris L.) AND CUCUMBERS (Cucumis sativus L.I TO EDIE—APPLICATIONS 0F ETHALFLURAEINT’ .................. 50- ABSTRACT .............. p ...................................... 50 INTRODUCTION ................................................ 51 METHODS AND MATERIALS ....................................... 53 EFFECTS OF ETHALFLURALIN ON GERMINATING BEANS .......... 53 EFFECTS OF ETHALFLURALIN ON GERMINATING CUCUMBERS ...... 53 DIFFERENTIAL TOLERANCE STUDIES: CULTURAL PRACTICES ..... 53 BEAN STUDY ............................................. 54 CUCUMBER STUDY ......................................... 54 RESULTS AND DISCUSSION ...................................... 55 EFFECTS OF ETHALFLURALIN ON GERMINATING BEANS .......... 55 iv Page EFFECTS OF ETHALFLURALIN ON GERMINATING CUCUMBERS ...... 55 DIFFERENTIAL BEAN CULTURAL TOLERANCE STUDY ............. 60 DIFFERENTIAL CUCUMBER CULTURAL TOLERANCE STUDY ......... 67 LITERATURE CITED ............................................ 71 CHAPTER 4 - ABSORPTION AND TRANSLOCATION 0F 14C-ETHALFLURALIN IN CUCUMBER (Cucumis sativus L. cv Green Star), BEAN (Phaseolus vulgaris L. cv Seafarer) AND PEA (Pisum sativum L. cv Sparkle) ........................ 73 ABSTRACT .................................................... 73 INTRODUCTION ................................................ 74 METHODS AND MATERIALS ....................................... 76 FIELD STUDY ............................................ 76 GREENHOUSE STUDIES ..................................... 79 RESULTS AND DISCUSSION ...................................... 82 FIELD STUDY ............................................ 82 GREENHOUSE STUDIES ..................................... 88 LITERATURE CITED ........................................... 104 APPENDIX ........................................................ 107 BIBLIOGRAPHY .................................................... 111 LIST OF TABLES Table CHAPTER 1 Page 1 Common and chemical nomenclature of selected dinitroaniline herbicides ............................ 6 CHAPTER 2 1 Weed control and crop injury ratings after pretransplant surface herbicide application in muskmelons at location I in 1979 .................. 30 2 Response of transplanted muskmelon and weeds to ethalfluralin- mulch combinations at location I in 1980 ............................................ 33 3 Response of seeded muskmelons to preemergence surface applications of ethalfluralin at location II in 1981 ........................................... 36 4 Weed and pickling cucumber response to preemergence herbicide applications at location I in 1979 ............................................ 37 5 Response of weeds and seeded pickling cucumbers to preemergence surface applications of ethalfluralin at location 11 in 1981 ................. 40 6 Response of weeds and seeded slicing cucumbers to preemergence surface application of ethalfluralin at location II in 1981 ................. 41 7 Response of weeds and seeded watermelon to preemergence surface applications of ethalfluralin at location II in 1981 ................. 42 8 Weed control and crop response after preemergence surface applications of ethalfluralin in direct seeded summmer squash at location II in 1981 ......... 44 9 Weed and crop response to preemergence applications of ethalfluralin in seeded winter squash at location 11 in 1981 .................................. 45 vi Table 10 CHAPTER 2 Page Weed and crop response after preemergence applications of ethalfluralin to direct seeded pumpkins at location II in 1981 ...................... 46 CHAPTER 3 Phytotoxicity ratings of bean cultivars after preplant applications of ethalfluralin ............... 63 Average dry weight of untreated beans and influence of ethalfluralin on shoot dry weight production as a percent of control ................................. 64 Correlation coefficients for fresh weight and phytotoxicity ratings, percent dry weight and phytotoxicity rating and for percent dry weight and percent fresh weight of seven bean cultivars treated with ethalfluralin at 1.12, 2.24, 4.48 or 8.96 kg/ha ........................................... 66 Phytotoxicity ratings and influence of ethalfluralin (1.12 kg/ha) on shoot dry weight production as a percent of control ................................... 68 CHAPTER 4 14C-residue in cucumber tissue following preemergence soil applications of 14C- ethalfluralin at 1.68 and 3.36 kg/ha ................. 83 14C-residue in beans following preplant incorporated treatments of 14C- ethalfluralin at 1.68 and 3.36 kg/ha ................. 85 Volatilization and absorption of 14C-ethalfluralin by cucumber seedlings ................................ 89 Distribution of 14C in cucumber and bean seedlings following root exposure to 14C-ethalfluralin .......... 90 Distribution of 14C in cucumber and bean seedlings following stem exposure to 14C-ethalfluralin ......... 96 Distribution of 14C in cucumber and bean seedlings following cotyledon exposure to 14C-ethalfluralin...100 Extraction and phase separation Of radioactivity in cucumbers and beans after 2, 6, 24 or 48 h root exposure to 14C-ethalfluralin ....................... 101 vii Table A1 A2 A3 APPENDIX Page Soil analysis of Spinks loamy sand .................. 107 Extraction and phase separation of radioactivity in cucumbers after 2, 6, 24 or 48 h root exposure to I4C-ethalf1ura1in ................................... 108 Extraction and phase separation of radioactivity in c- beans after 2, 6, 24 or 48 h root exposure to 1 ethalfluralin ....................................... 109 viii Figure LIST OF FIGURES CHAPTER 1 Page Structure of selected 2,6-dinitroaniline chemistry ............................................ 5 CHAPTER 3 Bean seedlings germinated in petri dish with ethalfluralin at 0 ppm (A) and 100 ppm (B) ........... 57 Cucumber seedlings germinated in petri dishes with ethalfluralin at O and 351 ppm (A), 0 and 35.1 ppm (B), and with 0 and 3.51 ppm (C) ............ 59 'Black Magic' (A), a tolerant bean cultivar and 'Spartan Arrow' (8), a susceptible cultivar germinated in soil with ethalfluralin incorporated at 0, 1.12, 2.24, 4.48 and 8.96 kg/ha (left to right) ................................. - .............. 62 CHAPTER 4 Distribution of radioactivity in a bean plant 2 weeks after treatment with soil applied 14C- ethalfluralin. The plant specimen is on the left and the autoradiograph on the right ............. 87 Distribution of radioactivity in a bean plant 4 weeks after treatment with soil applied 14C- ethalfluralin. The plant specimen is on the left and the autoradiograph on the right ............. 87 Distribution of radioactivity in a cucumber seedling after 6 hours exposure to 14C-ethalfluralin. The plant specimen is on the left and the autoradiograph on the right .......................... 87 Distribution of radioactivity in bean seedlings 24 h after treatment with 14C-ethalf1uralin to (A) the root system, (B) the stem and (C) a single cotyledon. The plant specimen is on the left and the corresponding autoradiograph on the right....93 ix Figure CHAPTER 4 Page Distribution of radioactivity in cucumber seedlings 24 h after treatment with 14C-etha1f1ur- alin to (A) the root system, (B) the stem and (C) a Single cotyledon. The plant specimen is on the left and the corresponding autoradiograph on the right ............................................ 95 Microradiographs of cucumber and bean seedlings following topical stem applications of 14C- ethalfluralin: (A) cucumber stem above application zone 6 h post treatment (X300); (8) cucumber stem vascular tissue above application zone 6 h post treatment (X300); (C) cucumber stem vascular tissue below application zone 6 h post treatment (X875); (0) cucumber leaf vascular tissue 8 h post treatment (X300); (E) bean stem tissue near epidermis above treatment zone 8 h post treatment (X300); (F) bean stem vascular tissue above treatment zone 8 h post treatment (X300) ..................................... 99 INTRODUCTION Weeds not only compete with crop plants for moisture, nutrients and light by may also interfere with crop harvesting and lower crop quality. Crops, such as cucumber (Cucumis sativus L.), which have a prostate growth habit may be at a disadvantage in competing with established weeds such as redroot pigweed (Amaranthus retroflexus L.) and common lambsquarters (Chenopodium album L.) which have an upright growth habit. The spreading vine growth and shallow root system of cucumbers makes mechanical control of weeds difficult without incurring some degree of injury to the cucumber crop. From a practical standpoint, chemical weed control is often preferred over mechanical type control methods. Few herbicides are currently registered for use in cucurbit crops. The recent removal of CDEC (2-chloroallyl diethyldithiocarbamate) and chloramben-methyl ester (3-amino-2,5-dichlorobenzoate) from the market further limited the availablity of herbicides to the cucumber growers. The introduction of selective postemergence graminacides such as diclofop (2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid) may allow growers to effectively control grass type weeds in cucurbit crops. However, the chemical control of broadleaved weeds in cucurbits remains a difficult task for producers using the limited number of products currently available. Early reports indicated that the dinitroaniline herbicide, ethalfluralin (N-ethyl-N-(2-methy1-2-propeny1)-2,6-dinitrO-4-(tri- fluotomethyl)benzenamine) controlled many of the broadleaved and grass weed species prevalent in cucurbit production. This study had three objectives, the first being to determine the response of selected cucurbit crops and annual weed species to soil applications Of ethalfluralin, secondly, to determine if selected bean (Phaseolus vulgaris L.) and cucumber cultivars exhibit differ- ential tolerance, and third, to Characterize the uptake and trans- 14 location of C-ethalfluralin in beans, cucumbers and peas (Pisum sativum L.). CHAPTER 1 DINITROANILINE HERBICIDES - A LITERATURE REVIEW HISTORY In 1960, Alder et a1. (1) first reported on the herbicidal properties of the 2,6-dinitroanilines. Since the initial disclosure Of the herbicidal activity of this class of compounds by Eli Lilly Research Laboratories, many companies have developed and marketed herbicides based on similar chemistry. Although all dinitroaniline herbicides are derived from the same basic 2,6—dinitroaniline molecule, varied substitutions have lead to unique differences in both the chemical properties and biological activities of these herbicides. The dinitroaniline herbicides are used for selective preemergence control of annual grass and broadleaved weeds (2,61). The comparative toxicity of dinitroaniline herbicides vary greatly among plant species (8,22,31,39). Factors such as timing of applications, methods Of application, depth of incorporation, soil moisture levels and rates of of dinitroaniline applications all contribute to differential selectivity of these herbicides. PHYSICAL AND CHEMICAL PROPERTIES Chemical structures Of selected 2,6-dinitroaniline chemistry are shown in Figure 1. With selected chemical substitutions at R1, R2 and R3, both the physical and biological properties of the compound are altered. Members of the dinitroaniline class of herbicides (Table 1) are, in general, yellow-orange, have a low water solubility, are soluble in a wide range of organic solvents and are somewhat volatile (2). The melting points of the dinitroaniline herbicides range from 42 C for fluchloralin to 152 C for nitralin and prosulfalin. Trifluralin, with a pressure of 1.99 x 10 mm Hg 0 29.5 C, is one of the more volatile dinitroaniline herbicides while nitralin exhibits one of the lowest '8 mm Hg @ 25 C. Physical properties Of vapor pressures at 1.8 x 10 ethalfluralin are: yellow-orange crystalline solid, faint amine odor, melting point 57-59 C, decomposes at 256 C, susceptible to decom- position by ultraviolet irradiation, vapor pressure - 8.2 x 10'5 mm Hg 0 25 C, solubility (25 C) ->5500 mg/ml in acetone, acetonitrile, chloroform, methylene chloride or xylene, 82-100 mg/ml in methanol and 0.3 ppm in water (61). FATE IN PLANTS Uptake and Translocation. The site of maximum uptake Of a dinitro- aniline herbicide varies among plant species. In general, the Shoot of monocots and the hypocotyl or hypocotyl hook of dicots are the major sites of dinitroaniline herbicide uptake. Barrentine and Warren (7) H-N-H OZN <::::::) NO2 Basic Structure Points of Substitution ‘IH3 CH3'CH2'N‘CH2'C:CH2 O N N0 2 2 CF3 Ethalfluralin Figure 1. Structure of selected 2,6-dinitroaniline chemistry. w=_u23256-a-fixaoea_e-z-z-oeu_=_u-o.~-oco=~cweuia.a.a m:_eu2uc_=m~»;pmswu-m.m-m_>coc_=mfl_>:wcaoeu_=wc-m.m-Ao:_5a~»aocauev-auu-z m:_u_:“ovum-~>aoca-z-oepwc_u-m.m-oco=~c_cg-a.a.a-fichpmefixaocao_uxuv-z m=_2a=a~=anoap_=we m.~-_»;paefle 4.M-A~»aoea_>;um-.v-z :_~aL=_c_LP :_~m$~=moea cwfimcz_moca :__ezgasue=ma aeuEa__cacfizm_>aocawu-.2..z-oepu=_u-m.m =__a~xeo 5:23_:e~»aoaaun-z.2-0Lpu:_e-o.N-A~S=OC_=m~>;Smsv-a :__aep_z mcflu_szo_xaoca_cuz.z-ocp_:AUIo.N c_~maocqomH a:_~_=mAfixzumsoeoaficflepv-a-usaoea-z-oep_cuu o.N-A_>;pmoeoficu-~v-z =_~eco~;u=_a , mcfismcm~cwa Adxzuaeoeo=_c_apv-e-oep_:3v-0.N-AA»:maoea-~-fizzums-mv-z-_szpa-z =__aeaficgacpm muggeue-e.~-a:a=_opoepuc_u-m.m-oeo=~E_Lp-a.a.a-_»cpaue-.z..2 m=_5aep_:_a a=_se=wN:mnoepw=_u-e.N-A_xaoeazuzpme-_v-2-flfixcamdszpmeuu-_..V-4 cwdaepzm m=_u_=_5pum-oep_cwu-o.N-oeo=~c_ep-a.a.a-_»pzm-z-_xaan-z =_cw=mm mEmz _muwsmcu mamz coeeoo .mmcwo_ncmc m:__flccocpfl:_u umpuwfimm do mczum_o:msoc ~mu_emcu can coesou ._ w~nwh 7 reported that the coleoptilar node of sorghum (Sorghum bicolor (L.) Moench) and the hypocotyl hook of cucumber (Cucumis sativus L.) were the most susceptible sites, as well as the sites of maximum 14C-trifluralin and 14 C-nitralin uptake. In another study (6), they found that trifluralin was more toxic than nitralin to the shoots of sorghum and cucumber via shoot exposure while nitralin was more toxic to the roots via root exposure. Parker (43) reported that trifluralin can exert its action through shoot uptake, but root uptake appeared to be much more effective in a hybrid sorghum (S. vulgare x sudanense cv Sudax). Derr and Monaco (13) exposed shoots or roots of cucumber to ethalfluralin and found that both shoots and roots absorbed the herbicide, but exposure of roots to ethalfluralin was more toxic than shoot exposure. Jacques and Harvey (30) exposed roots or shoots of oats (Avena sativa) and peas (Pisum sativum) to vapors of 14C- labeled benefin, dinitramine, fluchloralin, oryzalin, profluralin and trifluralin. They found that, except for oryzalin, all of the herbicides were absorbed by both roots and shoots Of germinating oats and peas. These investigators also reported that, in general, vapor absorption was correlated with rates of herbicide volatilization. Numerous investigators have demonstrated the vapor activity of dinitro- aniline herbicides (21,28,40,55). Harvey (21) suggested that vapor absorption of these herbicides may be more important than absorption from the soil solutions. However, the absorption of oryzalin vapors may be less important, because of its lower vapor pressure, than absorption from the soil solution (28,30). The degree to which dinitroaniline herbicides are translocated in plants varies both among plant Species and the herbicide compounds. For example, root applied 14C-dinitramine readily translocated to the shoots of barnyardgrass (Echinochloa crus-galli (L.) Beauv.), sorghum, Palmer amaranth (Amaranthus palmeri S. Hats.) and soybean (Glycine max 14C-profluralin was translocated (23). L. Merr.) while very little Jacques and Harvey (30) detected translocation of root absorbed vapors 14 of C-labeled benefin, fluchloralin, profluralin and trifluralin into pea shoots while little herbicide translocation was observed in oats. They reported that no shoot-root transport could be detected in either 14 peas or oats. Little translocation of C-trifluralin and 14C-nitralin occurred after application to cucumber cotyledon or the hypocotyl hook 14 14 (7). However, C from C-trifluralin applied as a cotyledon treat- ment was distributed in both cotyledons 96 h after treatment. Strang and Rogers (54) conducted a microradioautographic study of 14C-trifluralin absorption in cotton (Gossypium hirsutum L.) and 14 soybean. They found that radioactivity from C-trifluralin was retained primarily on the root surface in both species. Radioactivity was noted in the walls Of both xylem vessels and cortical cells of roots. Little translocation out of soybean roots was observed, but limited translocation into leaves of cotton, apparently via the metaxylem was noted. Accumulation of radioactivity in the protoxylem of the cotton stem was also observed. They noted that breaks in the epidermis of the roots greatly facilitated the entrance of radioactivity into the roots. Metabolism. As in the case of dinitroaniline herbicide transloca- tion, the metabolism of these herbicides varies among plant species and 9 compounds. Much of the plant metabolism work that has been reported for these herbicides was conducted by applying 14C-labeled compound to the soil in which test plants were grown, after which, 14 C-labeled compounds extracted from the plant were identified. This experimental procedure raises a question to whether the plant metabolized the compound, if the metabolism occurred in the soil and the resulting metabolites were absorbed, or a combination of both procedures occurred. Golab et a1. (18) applied 14C-labeled trifluralin to greenhouse soil in which carrots (Daucus carota L.) were grown. The carrots were harvested 110-days after treatment, extracted with methanol and the 14C-residue assayed. A majority (74.4%) of the 14 C was observed in the peel Of the root while 25.6% was found in the root pulp. Chromatographic results showed that parent trifluralin was the major source of radio- activity in roots (89.0%) while the major conversion product was a,a,a-trifluoro-Z,6-dinitrO—N-(nfpropyl)5pftoluidine (4.7%). In leaf extracts, only 40% of the 14 4 C appeared to be parent trifluralin while 50% of the extracted 1 C exhibited polar properties. Two other products, tentatively identified as a,a,a-trif1uoro-5-nitro- N4-(g-propyl)-toluene-3,4-diamine (1.4%) and 4-(difinfpropyl-amino) 3,5-dinitrobenzoic acid (4.8%), were observed in roots extracts. Golab and Althaus (16) exposed tomato (Lycopersicon esculentum Mill.), pepper (Capisicum frutescens L.), tobacco (Nicotiana tabacum L.) and wheat (Triticum aestivum L.) to soil applied 14C-isopropalin. Although the parent compound and 12 degradation products were identified in soil, no parent compound or known transformation products were 14 identifiable in plant extracts. Only negligible amounts of C were 10 detected in plant tissue. The metabolism of 14 C-trifluralin was examined by Biswas and Hamilton (9) in both whole plant and crude extracts of peanuts (Arachis hypogaea L.) and sweet potatoes (Ipomoea batatas (L.) Lam.). They found in both species that trifluralin was converted to compounds which were somewhat more polar in nature than parent trifluralin. Less than 1% of the total extracted 14C from peanut plants was identified as trifluralin, while a greater percentage (17%) was detected in sweet potatoes. An intermediate dealkylated degradation product (a,a,a-trifluorO-2,6-dinitro-N-(nfpropyl)-p;toluidine) was detected 14 (1.2% of total C) in whole plant extracts of peanut but not in 14 sweet potato extracts. Two additional unidentified C-products were found in peanuts and three unidentified compounds were found in sweet potatoes. Degradation products were also observed when crude extracts 14 of both peanut and sweet potatoes were incubated with C-trifluralin. These researchers suggested that a partial dealkylation of the N,N-di- propyl moiety of the trifluralin molecule preceded a reduction of the nitro-groups in the crude extracts of peanuts. 14 Soil-incorporated C-benefin was absorbed into peanut and alfalfa (Medicago sativa L.) plants (17). After 129 days exposure, 2.33 ppm 14 C-benefin was incorporated into peanut plant tissue. The non- extractable radioactivity was determined in peanut stems (75%), leaves (43%), hulls (14%) and nut meats (37%). The degradation 4C-residues of plant tissues were products found in the extractable 1 essentially those products found in soil, but in very low concentrations. Significant amounts of decomposition products were found only in stem, 11 root and hull tissue. Plant Responses. The dinitroaniline herbicides apparently do not inhibit seed germination, even in susceptible plant species (41). How— ever, they may inhibit growth of the entire plant in susceptible species (4). The inhibition of root development by these herbicides has been demostrated in numerous plant species by several investigators (35,38, 56). Talbert (52) and Lignowski and Scott (34) found that trifluralin inhibited mitosis in the roots Of soybeans, onion (Allium cepa L.) and wheat. The induction of root tip swelling is often observed in herbicide treated roots (35,56). Cells in the meristematic regions Of treated roots are Often multinucleate (34,53,57). The exogenous applications of D-a-tocopherol acetate has been demonstrated to decrease the inhibition of tissue growth caused by dinitroaniline herbicides (2). The root swelling effect of dinitroaniline herbicides has been reduced by applications of 2,3-dimercaptopropanol (35). Moreland and Huber (37) reported that 12 dinitroaniline herbicides were shown to interfere with electron transport and phosphorylation in isolated mung bean (Phaseolus aureus Roxb.) mitochondria. All of the compounds tested inhibited the rate of valinomycin-induced mitochondrial swelling in isotonic KCl within the same concentration range that caused inhibition of state three respiration. They postulated that dinitroaniline herbicides partition into the inner mitochondrial mem- brane, thereby decreasing membrane fluidity, and altering membrane permeability. Barns and Krieg (5) noted a reduction in the photosynthetic rate of tomatoes after applications of trifluralin. 12 Schultz et al. (53) reported that synthesis of RNA, DNA and protein was suppressed in corn (£29.99X§.L-) root tips germinated in trifluralin but no significant effect was observed in the shoots. Penner and Early (47) found that trifluralin markedly reduced RNA synthesis based on analysis of isolated chromatin from treated corn seedlings. They postulated that the trifluralin was bound to the chromatin thus causing a reduction of template availablity for transcription. Trifluralin was not Observed to inhibit chromatin activity in soybean seedlings. FATE IN SOILS Once a herbicide is applied to the soil, losses in activity can occur through volatility, leaching, adsorption, photodegradation, microbial degradation and chemical degradation. Volatility. Because of high volatility, major losses in activity can occur with many dinitroaniline herbicides. Bradsley et a1. (12) reported that vapor loss of trifluralin increased with herbicide con- centration and soil moisture content and that losses decreased with subsurface placement in soil. Parochetti and Hein (45) compared the volatility of nitralin, trifluralin and benefin from a loamy sand under varying conditions of temperature and soil moisture. They found that volatility of both trifluralin and benefin increased with increasing temperatures of 30, 40 and 50 C and with increasing soil moisture from air dryness to field capacity. In a laboratory study, no volatilization of nitralin was detected but 24.5% and 12.5% of 13 trifluralin and benefin, respectively, volatilized from a loamy sand after 3 h at 50 C and with soil moisture at field capacity. In a later Study, Parochetti et a1. (44) evaluated the volatility of 11 dinitro- aniline herbicides from three different soil types. They reported no detectable volatility Of nitralin or oryzalin in their 3 h laboratory study with a moist sandy soil while vapor losses of benefin, proflur- alin and trifluralin approached 25% under the same conditions. Soil type influenced not only the degree of volatilization but also the relative rate of volatility among dinitroaniline herbicides. Kennedy and Talbert (32) assessed the effects Of soil moisture on volatiliza- tion losses of several surface applied dinitroaniline herbicides from a TalOka silt loam. Losses Of butralin, nitralin, oryzalin and isopropa- lin after 24 h were not increased when soil moisture was increased from 1% to 14%, 26% or 33%. The loss of fluchloralin (9%), benefin (20%) and trifluralin (17%) at 1% soil moisture increased to 80%, 89% and 94%, respectively, at 33% soil moisture. The losses of dinitramine and profluralin also increased with increasing soil moisture. In compounds affected by soil moisture, the trifluoro-methyl group was a common structural component. Savage (50) reported that over an 8-day period, significantly more trifluralin and ethalfluralin volatilized from a Bosket sandy loam when the moisture content was equivalent to field capacity than when the soil was either air-dried or flooded. Losses of dinitroaniline herbicides from volatilization can be reduced by incorporating the herbicide into the soil (32,51), in fact manufac- turer's label instructions require incorporation to maximize herbicidal activity. 14 Photodegradation. The dinitroaniline herbicides are generally considered sensitive to UV irradiation as a result of studies conducted on glass surfaces, in solvents and as a vapor (20,33,36,51). The importance of photodecomposition of soil applied dinitroaniline herbi- cides is not totally resolved. Wright and Warren (60) found that tri- fluralin photodegraded on soil surfaces but at a rate much reduced from that on a glass surface. In a later study, Parochetti and Hein (45) irradiated soil treated with trifluralin, benefin or nitralin for either 24 h or 72 h. They found no positive evidence for photodecomposition and speculated that the uneven soil surfaces provide protection from direct radiation thus greatly minimizing photodecomposition. Kennedy and Talbert (32) exposed soil coated TLC plates treated with dinitro- aniline herbicides to UV light for 24 h while maintaining the ambient temperature at 5 C to minimize volatility. They found dinitramine to be greatly affected by UV light while no significant differences were found among benefin, butralin, fluchloralin, isopropalin, nitralin, oryzalin, profluralin and trifluralin. Soil Movement. Herbicides can move in soil systems either as vapors or as solutes in the soil water phase. The degree to which a compound is adsorbed to soil, volatilized, or soluble in water determines the extent to which it moves in the soil system. Although the dinitroaniline herbicides are structurally related, they behave differently in the soil system. Several researchers have shown that trifluralin movement in soil is primarily by vapor diffusion (10,11, 27). The rate of diffusion was found to be dependent upon relative soil moisture and air-filled porosity. Jacques and Harvey (27) reported 15 that diffusion of trifluralin, profluralin and benefin in a Plano Silt loam decreased as soil water increased. The diffusion of dinitramine and fluchloralin did not change with soil water content. Oryzalin reached highest mobility in a water saturated soil, though none Of the herbicides moved more than 10 mm in the soil over a 17-day period. The dinitroaniline herbicides are not readily leached in soil, therefore, loss by this mechanism is not considered important (3,42,61). Weber (58) reports that dinitroaniline herbicides exist in the undis- solved form in the soil and become associated with the lipophilic fraction Of organic soil colloids. Once bound, these herbicides have greatly reduced biological activity. Millier et al. (3) reported that when trifluralin, nitralin and benefin were applied for five consecutive years as soil-incorporated treatments to cotton, herbicide residues were confined to the tilled zone of soil (upper 30 cm), and about 80 % of the residue was in the upper 15 cm of soil. Adsorption. The binding of dinitroaniline herbicides to soils and resulting reduction in their phytotoxicities is directly related to the organic matter content of the soil (24,25,48). Hollist and Foy (25) found that in the case of trifluralin, anion exchange capacity was a better parameter than cation exchange capacity for predicting the potential of an adsorptent to reduce phytotoxicity. Microbial/Chemical Degradation. The dinitroaniline herbicides are relatively nonpersistant in soil, with most biological activity dissi- pating within six months under warm, hunid conditions (20,27,42,50). Gingerich and Zimdahl (14) found that both isopropalin and oryzalin 16 dissipated more rapidly under anaerobic than aerobic soil conditions. Trifluralin also degraded more rapidly under anaerobic conditions (46, 49). Willis et a1. (59) associated this effect to the redox potential in anaerobic soil systems. The degradation of dinitroaniline herbi- cides in soil systems is directly correlated with temperature and soil moisture content (29,62). The chemical degradation pathways of dinitroaniline herbicides in soil systems appears to be complex. Golab et al. (15,19) identified 28 degradtion products of trifluralin and postulated a complex set of pathways for trifluralin transformation in field soil. They also indicated that the trifluralin degradation product, a,a,a-trifluoro- toluene-3,4,5-triamine, appeared to be a key compound in the formation of soil-bound residues. NumerOus soil degradation products have also been identified for other dinitroaniline herbicides (16,17). 10. 11. 12. 13. 14. LITERATURE CITED Alder, E.F., W.L. Wright, and Q.F. Spoer. 1960. Control of seedling grasses in turf with diphenylacetonitrile and a substituted dinitroaniline. Proc. North. Cent. Weed Control Conf. 17:23-24. Anderson, W.P. 1977. Weed Science: Principles. West Publishing CO., New York. 598 pp. Anderson, W.P., A.B. Richards and J.W. Whitworth. 1968. Leaching of trifluralin, benefin, and nitralin in soil columns. Weed Sci. 16:165-169. Ashton, F.M. and A.S. Crafts. 1973. Mode of action of herbicides. John Wiley & Sons, New York. 504 pp. Barnes, L.W. and D.R. Krieg. 1973. Evidence for a trifluralin- potassium nitrate interaction affecting tomato seedling growth. Crop Sci. 13:489-490. Barrentine, W.L. and G.F. Warren. 1971. Shoot zone activity of trifluralin and nitralin. Weed Sci. 19:37-41. Barrentine, W.L. and G.F. Warren. 1971. Differential phytotox- icity of trifluralin and nitralin. Weed Sci. 19:31-37. Billett, D. and R. Ashford. 1978. Differences in phytotoxic response of wild oats (Avena fatua) to triallate and trifluralin. Weed Sci. 26:273-276. Biswas, P.K. and W. Hamilton, Jr. 1969. Metabolism of triflur- alin in peanuts and sweet potatoes. Weed Sci. 17:206-211. Bode, L.E., C.L. Day, M.R. Gerhardt and C.E. Goering. 1973. Mechanism Of trifluralin diffusion in Silt loam soil. Weed Sci. 21:480-484. Bode, L.E., C.L. Day, M.R. Gerhardt and C.E. Goering. 1973. Prediction of trifluralin diffusion coefficients. Weed Sci. 21:485-489. Bradsley, C.E., K.E. Savage and J.C. Walker. 1968. Trifluralin behavior in soil. II. Volatilization as influenced by concen- tration, time, soil moisture content, and placement. Agron. J. 60:89-92. Derr, J.F. and T.J. Monaco. 1982. Ethalfluralin activity in cucumber (Cucumis sativus). Weed Sci. 30:498-502. Gingerich, L.L. and R.L. Zimdahl. 1976. Soil persistence of isopropalin and oryzalin. Weed. Sci. 24:431-434. 17 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 18 Golab, T., W.A. Althaus and H.L. Wooten. 1979. Fate of [14C] trifluralin in soil. J. Agric. Food Chem. 27:163-179. Golab, T. and W.A. Althaus. 1975. Transformation of isopropalin in soil and plants. Weed Sci. 23:165-171. Golab, T., R.J. Herberg, J.V. Gramlich, A.P. Raun, and G.W. Probst. 1970. Fate of benefin in soils, plants, artificial rumen fluid and the ruminant animal. J. Agric. Food Chem. 18:838-844. Golab, T., R.J. Herberg, S.J. Parka, and J.B. Tepe. 1967. Metabolism of carbon-14 trifluralin in carrots. J. Agric. Food Chem. 15:638-641. Golab, T., and J.L. Occolowitz. 1979. Soil degradation of trifluralin: Mass spectrometry of products and potential products. Biomedical Mass Spectrometry. 6:1-9. Harrison, R.M. and D.E. Anderson. 1970. Soil analysis of trifluralin. Methodology and factors affecting quantitation. Agron J. 62:778-781. Harvey, R.G. 1974. Soil adsorption and volatility of dinitro- aniline herbicides. Weed Sci. 22:120-124. Harvey, R.G. 1973. Relative phytotoxicities of dinitroaniline herbicides. Weed Sci. 21:517-520. Hawxby, K. and E. Basler. 1976. Effects of temperature on absorption and translocation of profluralin and dinitramine. Weed Sci. 24:545-548. Helling, C.S. 1975. Dinitroaniline herbicide bound residues in soil. Pages 366-367 in 0.0. Kaufman, G.G. Still, G.D. Paulson and S.K. Bandal, eds.‘_Bound and conjugated Pesticide Residues, American Chem. Soc., Washington, D.C. Hollist, R.L. and C.L. Foy. 1971. Trifluralin interactions with soil constituents. Weed Sci. 19:11-16. Huffman, J.B. and N.D. Camper. 1978. Growth inhibition in tobacco (Nicotiana tabacum) callus by 2,6-dinitroaniline herbicides anderotection by d-a-tocopherol acetate. Weed Sci. 26:527-530. Jacques, G.L. and R.G. Harvey. 1979. Adsorption and diffusion of dinitroaniline herbicides in soils. Weed Sci. 27:450-455. Jacques, G.L. and R.G. Harvey. 1979. Dinitroaniline herbicide phytotoxicity as influenced by soil moisture and herbicide vaporization. Weed Sci. 27:536-539. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 19 Jacques, G.L. and R.G. Harvey. 1979. Persistence of dinitro- aniline herbicides in soil. Weed Sci. 27:660-665. Jacques, G.L. and R.G. Harvey. 1979. Vapor absorption and translocation of dinitroaniline herbicides in oats (Avena sativa) and peas (Pisum sativum). Weed Sci. 27:371-374. Jordan, T.N., R.S. Baker and W.L. Barrentine. 1978. Comparative toxicity of several dinitroaniline herbicides. Weed Sci. 26:72- 75. Kennedy, J.M. and R.E. Talbert. 1977. Comparative persistence of dinitroaniline type herbicides on the soil surface. Weed Sci. 25:373-381. Ketchersid, M.L., R.W. Bovey, and M.G. Merkle. 1969. The detection of trifluralin vapors in air. Weed Sci. 17:484-485. Lignowski, E.M. and E.G. Scott. 1972. Effects of trifluralin on mitosis. Weed Sci. 20:267-270. Lignowski, E.M. and E.G. Scott. 1971. Trifluralin and root growth. Plant Cell Physiol. 12:701-708. Messersmith, C.G., 0.C. Burnside and T.L. Lavy. 1971. Biological and non-biological dissipation of trifluralin from soil. Weed Sci. 19:285-290. Moreland, D.E. and S.C. Huber. 1979. Inhibition of phytosyn- thesis and respiration by substituted 2,6-dinitroani1ine herb- icides. 111. Effects on electron transport and membrane properties of isolated mung bean mitochrondria. Pestic. Biochem. Physiol. 11:247-257. Murray, D.S., J.E. Street, J.K. Soteres, and G.A. Buchanan. 1979. Growth inhibition of cotton (Gossypium hirsutum) and soybean (Gl cine max) roots and shoots by three dinitroaniline herbicides. Wee ci._27:336-342. Murray, D.S., P.W. Santelmann, and H.A.L. Greer. 1973. Differ- ential phytotoxicity of several dinitroaniline herbicides. Agron. J. 65:34-35. Negi, N.S. and H.H. Funderbunk, Jr. 1968. Effect of solutions and vapors of trifluralin on growth of roots and shoots. Abstr. Weed Sci. Soc. Amer. pp. 37. Parka, S.J. and 0.F. Soper. 1977. The physiology and mode Of action of the dinitroaniline herbicides. Weed Sci. 25:79-87. Parka, S.J. and J.B. Tepe. 1968. The disappearance of triflur- alin from field soils. Weed Sci. 17:119-122. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. 55. 56. 57. 20 Parker, C. 1966. The importance of shoot entry in the action of herbicides applied to the soil. Weed Sci. 14:117-121. Parochetti, J.V., G.W. Dec, Jr. and G.W. Burt. 1976. Volatility of eleven dinitroaniline herbicides. Weed Sci. 24:539-522. Parochetti, J.V. and E.R. Hein. 1973. Volatility and photo- decomposition of trifluralin, benefin and nitralin. Weed Sci. 21:469-473. Parr, J.F. and S. Smith. 1973. Degradation of trifluralin under laboratory conditions and soil anaerobiosis. Soil Sci. 115255-63. Penner, 0. and R.W. Early. 1972. Action of trifluralin on chromatin activity in corn and soybeans. Weed Sci. 20:364-366. Pritchard, M.K. and E.H. Strobbe. 1980. Persistence and phyto- toxicity of dinitroaniline herbicides in Manitoba soils. Can. J. Plant Sci. 60:5-11. Probst, G.W., T. Golab, R.J. Herberg, F.J. Holzer, S.J. Parka, C. Van der Schans and 0.8. Tepe. 1967. Fate of trifluralin in soils and plants. J. Agric. Food Chem. 14:592-599. Savage, K.E. 1978. Persistence Of several dinitroaniline herbicides as affected by soil moisture. Weed Sci. 26:465-471. Savage, K.E. and W.L. Barrentine. 1969. Trifluralin persistence as affected by depth of soil incorporation. Weed Sci. 17:349-352. Schultz, D.P., H.H. Funderburk and N.S. Negi. 1968. Effect of trifluralin on growth, morphology and nucleic acid synthesis. Plant Physiol. 43:265-273. Strang, R H. and R.L. Rogers. 1971. A microradioautographic study of I4C-trif1uralin absorption. Need Sci. 19:363-369. Swann, C.W. and R. Behrens. 1972. Phytotoxicity of trifluralin vapors for soil. Weed Sci. 20:143-146. Talbert, R.E. 1965. Effects of trifluralin on soybean root development. Abstr. Proc. 18th SO. Weed Cont. Conf. p 652. I Upadhyaya, M.K. and L.0. Nooden. 1978. Relationship between the induction of swelling and the inhibition of elongation caused by oryzalin and colchicine in corn roots. Plant & Cell Physiol. 19:133-138. Upadhyaya, M.K. and L.0. Nooden. 1977. Mode of dinitroaniline herbicide action. I. Analysis of the colchicine-like effects of dinitroaniline herbicides. Plant & Cell Physiol. 18:1319-1330. 58. 59. 60. 61. 62. 21 Weber, J.B. 1975. Fixed and biologically available soil bound pesticides. Pages 354-355 in_0.0. Kaufman, G.G. Still, G.D. Paulson and S.K. Bandel, eds. Bound and conjugated Pesticide Residues. Amer. Chem. Soc., Washington, D.C. Willis, G.H., E.L. Wander and L.M. Southwick. 1974. Degradation of trifluralin in soil suspension as related to redox potential. J. Environ. Qual. 3:262-265. Wright, W.L. and G.F. Warren. 1965. Photochemical decomposition of trifluralin. Weeds 13:329-331. WSSA Herbicide Handbook Committee. 1983. Herbicide Handbook 5th ed. Champaign, II. 515 pp. Zimdahl, R.L. and S.M. Gwynn. 1977. Soil degradation of three dinitroanilines. Weed Sci. 25:247-251. CHAPTER 2 RESPONSE OF SELECTED CUCURBIT CROPS AND ANNUAL WEED SPECIES TO SOIL APPLICATIONS OF ETHALFLURALIN ABSTRACT Three years Of field research were conducted at several locations to evaluate efficacy of ethalfluralin (N-ethyl-N-(2-methyl-2-propenyl)- 2,6-dinitro-4-(trifluoromethy1)benzenamine) as a selective herbicide applied either preplant incorporated (PPI) or as a preemergence (PRE) soil surface application in cucurbit crops. Clear plastic mulch increased growth of transplanted muskmelons (Cucumis melo L.) compared to no mulch, and improved crop tolerance to ethalfluralin applied at 1.68 kg/ha PPI. Injury was not observed on direct seeded muskmelons treated with PRE applications of ethalfluralin at 1.12 or 1.68 kg/ha. Direct seeded cucumbers (Cucumis sativus L.) were not injured by PRE applications of ethalfluralin at 1.12 to 2.52 kg/ha. Although direct seeded watermelon [Citrullus lanatus (Thumb.) Matsum. & Nakai] stands were reduced by 1.68 kg/ha (PRE), yields were not reduced from those of the untreated control. Direct seeded squash and pumpkin (Cucurbita sp.) were not injured by PRE applications of ethalfluralin at 1.12 or 1.68 kg/ha. Ethalfluralin applied PPI at 1.68 kg/ha afforded excellent control of common purslane (Portulaca oleracea L.). PRE applications at 1.12 or 1.68 kg/ha also resulted in excellent control of common purslane, common lambsquarters (Chenopodium album L.), redroot pigweed 22 23 (Amaranthus retroflexus L.) and large crabgrass [Digitaria sanguinalis (L.) Scop.]. 24 INTRODUCTION Cucumber (Cucumis sativus L.) production in Michigan is primarily for the processing market. The prolonged cool spring weather typical of Michigan, places fresh market production of muskmelon (Cucumis @219 L.) and other cucurbit crops at a disadvantage with the more southern production areas. The use of clear plastic mulch has been shown by Jacobson (11) to raise soil temperatures and by other investigators (5,6) to Often provide larger crop responses than black plastic mulch. A major disadvantage of using clear plastic is the need to use a herbicide under the mulch for control of weeds. Weeds in open fields can often rapidly overgrow the cucurbit crop and successfully compete for light, nutrients and moisture. Menges and Tamez (13) reported that weed competition can reduce cucumber yields by 36% when weeds are allowed to interfere for four weeks after crop emergence. Mechanical weed control is of limited practical use because the shallow spreading root system of cucurbit crops are subject to cultivation injury and the trailing vine growth limits cultivation to an early season practice. Only a few herbicides are currently available for weed control in cucurbit crops, due partially to the sensitive nature of cucurbits to herbicides. Differential cultivar tolerance to herbicides has also been reported in various cucurbit crops by several investigators (1,7, 14,15,17). The herbicides currently used in these crops include naptalam (N-1-naphthylphthalamic acid), bensulide [0,0-diisopropyl- phosphoro dithioate S-ester with N-(Z-mercaptoethyl)benzenesulfonamide], 25 DCPA (dimethyl tetrachloroterephthalate), dinoseb (2-sec-butyl-4,6- dinitro-phenol), and trifluralin (a,a,a-trifluoro-Z,6-dinitro-N,N- dipropyl-p-toluidine). These herbicides often do not provide adequate weed control and, at times, may cause injury to cucurbit crops (2,3,8, 9,13,15). Raboy and Hopen (16) investigated the use of starch xanthide formulations Of Chloramben (3-amino-2,5-dichlorobenzoic acid) as a possible means of improving both effectiveness and crop tolerance. Boldt (4) reported both excellent cucumber tolerance and good control of certain grass species was Obtained when dicloflop (2[4-(2,4- dichlorophenoxy)phenoxylpropanic acid) was applied postemergence. The dinitroaniline herbicide, ethalfluralin [N-ethyl-N-(Z-methyl-Z- propenyl)-2,6-dinitro-4-(trifluoromethyl)benzenamine] has been studied by several investigators (2,8,9,10,12,14,18) for its usefulness in cucurbits. Preplant incorporated treatments were observed to reduce cucumber tolerance compared to preemergence surface applications (10, 12,18). These studies were initiated to determine (a) if preplant incor- porated or preemergence surface applications of ethalfluralin influ- enced plant growth or yield of transplanted muskmelon, (b) if appli- cation of ethalfluralin under plastic mulch would influence tolerance of transplanted muskmelon to ethalfluralin and (c) if preemergence surface applications of ethalfluralin could provide acceptable weed control in a wide variety of cucurbit crops without producing excessive crop injury. 26 METHODS AND MATERIALS Experiments were conducted at two locations: I- Clarksville Horticulture Farm (Dryden sandy loam, 0.M.- 2.2%), II-Horticultural Research Center, (Metamora sandy loam, 0.M.- 1.5%). Annual weed species evaluated were large crabgrass [Digitaria sanguinalis (L.) Scop.), common lambsquarters (Chenopodium album L.), common purslane (Portulaca oleracea L.), redroot pigweed (Amaranthus retroflexus L.), common ragweed (Ambrosia artemisiifolia L.) and Sheperdspurse [Capsella bursa-pastoris (L.) Medik.]. Vegetable crops included were cucumbers (Cucumis sativus L. cvs Green Star and Marketmore 70), muskmelon (Cucumis melo L. cv Gold Star), pumpkin (Cucurbita pepo L. cv Howden), zucchini type summer squash (Cucurbita pepo L. cv Elite), acorn winter squash (Cucurbita pepo L. cv Table Queen), butternut winter squash (Cucurbita moschata L. cv Waltham Butternut) and watermelon [Citrullus lanatus (Thumb.) Matsum. & Nakai cv Summer Festival]. All treatments were applied with a C02 powered hand held plot sprayer that delivered 337 l/ha at 2.8 kg/cmz. Plots at all locations were irrigated when plants began to show moisture stress. All exper- iments were designed as randomized complete blocks with either three or four replications. Muskmelon Studies Experiment I. Herbicides (Table 1) were applied as surface applications immediately prior to transplanting muskmelon on June 4, 1979, at location I. Treatments were applied to four replications of 27 1.8 by 6.1 m single row plots. Weed control ratings were taken from four replicates 22 and 31 days after treatment (DAT). Fruit yields were taken 85 DAT from three replications that were maintained weed- free from 31 DAT. Experiment II. Ethalfluralin was applied at 1.68 kg/ha and incor- porated with a garden rototiller prior to applying plastic mulch treat- ments (Table 2) at location I on July 24, 1980. Treatments consisted of four replicates of 1.5 m by 7.6 m single row plots with 10 plants per plot. Muskmelon transplants were planted using a liquid fertilizer starter solution immediately after the treatments were applied. Crop vigor ratings were taken at 14 and 26 DAT. At 26 DAT, the number of nodes per plant, number of lateral stems per plant, stem length and mean internode length were determined for four plants per treatment in each replication. Weed control ratings were taken and mean number of fruit per plant, mean fruit weight per plant, mean fruit and mean plant weight were determined 49 DAT, with eight plants sampled per treatment in each replication. Experiment III. Ethalfluralin was applied at 1.12 and 1.68 kg/ha as preemergence surface applications to direct seeded muskmelon at location II immediately after planting on July 9, 1981 (Table 3). Treatments were applied to 1.8 m by 6.1 m single row plots that were replicated four times. Plant stand counts were taken 17 DAT and weed control ratings made 34 DAT. All plots were maintained weed-free from 37 DAT to harvest. At 98 DAT, mean fruit per plot, mean weight per plot and mean fruit weight were determined. 28 Cucumber Studies Experiment I. Herbicides (Table 4) were applied on June 16, 1979, as preemergence surface applications to direct seeded 'Green Star' cucumbers planted on June 13 in 1.8 by 6.1 m four row plots. All treatments were replicated four times. Crop injury ratings were taken at 31 and 45 DAT while weed control ratings were taken at 45 DAT. Three replicates were maintained weed-free from 45 DAT to 52 DAT after which fruits were harvested from the center two rows of each plot. The fruits were graded according to processing standards Of Pickle Packers International. Experiment II. On June 2, 1981, ethalfluralin was applied at 1.12 and 1.68 kg/ha as a preemergence surface application to direct seeded 'Green Star' cucumbers which were planted earlier the same day. The Single row plots were 0.9 by 6.1 m, and replicated four times. Plant stand counts were made 17 DAT, and weed control ratings were made 34 DAT. All plots were maintained weed-free from 37 DAT to 51 DAT after which yields were taken from the entire row. Experiment III. 'Marketmore 70' cucumbers were treated and ratings taken as described for experiment 11, except that mean fruit per plot, weight of marketable size (greater than 15 cm in length) fruit and weight of undersize fruits were obtained 64 DAT. Watermelon Study Watermelon were planted, treated and ratings taken the same as for cucumber experiment 11 except that plot size was 1.8 by 6.1 m and mean fruit per plot, mean yield per plot and mean fruit weight were taken 98 DAT. 29 Summer Squash Study Zucchini type summer squash plots were established and ratings taken as reported for cucumber experiment II except that mean number of fruit per plot, mean yield per plot and mean fruit weight data were taken 41, 45, 48, and 51 DAT. After emergence, all plots were thinned to achieve a 30 cm plant spacing. Winter Squash Studies Separate acorn and butternut squash studies were established as described for cucumber experiment II except plot size was 1.8 by 6.1 m and mean fruit per plot, mean yield per plot and mean fruit weight data were taken 120 DAT. All plots were thinned 45 DAT to achieve a 30 cm plant spacing. Pumpkin Study Direct seeded pumpkins were treated as described in cucumber experiment II except that 3.7 by 6.1 m plots were employed and mean fruit per plot, mean yield per plot and mean fruit weight data were collected 120 DAT. All plots were thinned to 8 plants per plot 45 DAT. RESULTS AND DISCUSSION Muskmelon Studies Experiment I. Ethalfluralin at 1.25, 1.96 and 2.52 kg/ha provided commercially acceptable control of common purslane and large crabgrass 22 DAT, but control of common purslane was noticeably reduced 31 DAT (Table 1). The 1.96 and 2.52 kg/ha rates of ethalfluralin also provided acceptable control of both redroot pigweed and common lambs- 30 .um::.a:ou. 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"wu<. .mgmpg5zu -5555. 502505 no.ou .ummzm.5 .oogumg "2555 .5:5.5.:5 :oesou "35o. ..cms.5me. .5..5 5555 u. 55.5 5. co..55555 o: "55 .5.55..55. .55 55.5555 5.55.5 .55.5 5..; 55.55..555 555. 55. 55555 555 .55.5\5.5.5 555 .55.5 ..5.» ..3 5555. .55.5 .5:..55 .55.> 55. 5.55 .5.55..555 .55 55.5555 5.55.5 5555 5..: 55.55..555 555. 55. 55555 555 5.555. 555555.5. 555 5.555. 55.5 ..55.5\.555.5. ..55.5\55555 55. 5.55 .555. .55 5.55 :5 55.55.55555. 5555 5:5 55.55555555. .55.55:55.555 55.55 55.. .5 55..555 5..5.5...55.55 .. 5. 5.. .5. 5.. 5. 5.55 5.5 5.5 5.. 5.5 .55.5. 555 5..555...55.5 5.5 5.5 55. 55.5 .5.5 ..5 5..5 5.5 ..5. 5.5 5.5 + 55.55 555.5 5..555.5.55.5 5.5 5.5 55.5 55.5 .5.5 5.5 5.55. 5.5 5.55 5.. 5. + 55.55 555.5 5..555...55.5 5.. 5.5 .5. 55. ... ..5 5.55 5.. 5.5. 5.5 5.5 + 5555.5555 5.5 5.5 55.. 55.5 5..5 5.5 5.55. 5.5 5.5. 5.5 5.5 55.55 555.5 5.5 5.5 55.5 55.5 5..5 5.5 5.55. 5.5 ...5 5.5 5.5 55.55 555.5 5.5 5.5 55. 5... 55.. 5.5 5..5 5.. 5.5. 5.. 5.5 5555.5555 .55. ..55. .55. .55.. ..55...|: 5555 5555 .55.5 .55.5 .2 55555 5.555. 5.555. .55.5 .55.5 .55 .55 .555.555. 5.5.5 \..55. .55.5 55.5. 55.5 ..5. .5555: 55 5. 555:, 5552 :55: :55: :55: 5552 :55: ..55 55. ..55 55. 5.55 55. 55..55 5 555.55 5.5... 5.555 5555... 5.555. 5. . :o..5uo. .5 5:5..55.5555 55.55 -5..555...55.5 5. 55553 555 55.555555 55.55.55555. .5 55555555 .5 5.55. 34 Commercially acceptable control of common purslane and common lambs- quarters was obtained with the application of 1.68 kg/ha ethalfluralin under clear mulch while severe weed growth was observed in the absence of herbicide. The weed growth under the clear mulch caused it to lift, and resulted in punctures and partial loss of anchoring of the plastic. Soil temperatures under the clear mulch were observed at times to be 5.5°C higher than temperatures under black mulch or the bare soil treatments. Plant growth and fruit yields in the ethalfluralin treatments were generally somewhat lower than in the comparative non- ethalfluralin treatments. These data support previous studies (5,6,11), which indicate that the culture of muskmelons on plastic mulch can provide significant yield advantages over bare ground culture. This observed growth advantage, under plastic mulch culture, was most likely due to increased soil temperature, increased retention of soil moisture and a reduction in soil compaction due to rainfall. Although the highest production was obtained in the clear mulch treatment, weed infestation caused unacceptable lifting and tearing of the plastic mulch. Based on this study, it is not possible to determine to what degree the competition effects of weeds in the clear plastic mulch treatment influenced musk- melon growth. However, it would be reasonable to expect conditions such as higher weed pressure, earlier weed competition or drought to to amplify the deleterious effects of weed competition under clear plastic mulch on muskmelon growth and yield. The use of ethalfluralin under clear plastic prevented serious infestations of common purslane and common lambsquarters. Significantly higher fruit yields were observed in the ethalfluralin + clear plastic treatment than either 35 the unmulched or black plastic mulch treatment. Experiment III. Preemergence surface applications of ethalfluralin at 1.12 and 1.68 kg/ha on direct seeded muskmelon gave commercially acceptable control of redroot pigweed, common lambsquarters and common purslane while not causing a reduction in crop stand as compared to untreated controls (Table 3). The mean fruit yield per plot (48.0 and 50.3 kg/ha respectively) observed for the 1.12 and 1.68 kg/ha ethal- fluralin treatments were about 60% greater than that obtained in untreated controls. The reduction in yields obtained in the untreated controls, compared to the ethalfluralin treatments, are most likely attributable to the early competitive effects of the high weed populations observed in this muskmelon study. Cucumber Studies Experiment I. There was no significant crop injury in any of the ethalfluralin treatments at either the 31 or 45 DAT rating period (Table 4). Although weed densities were low throughout all the plots in this experiment, a significant increase in weed control was observed with the higher rates of ethalfluralin as compared to the 1.25 kg/ha. There were no differences in any of the yield parameters measured between the untreated control and the singular ethalfluralin treatments. The increasing rates of ethalfluralin appeared to provide earlier yields possibly due to reductions in early season weed competition. The ethalfluralin + naptalam treatment resulted in lower total fruit yield (10.2 kg) when compared the untreated control (17.8 kg). The preemergence surface applications of ethalfluralin at all rates did not reduce total fruit yields from those obtained in untreated plots. 36 .mcmmmcaa coeeou "smog .empcmzcmnsm_ :oeeou nobou .umwzm_a poo; um; uzamm .Hcmspmmcu quwm mxmn up nmm:_poa .Pmmp cw HH coflpmuo_ um :fi_wL:~m~ocpw we mco_pmu_~aam moowcsm mucmmcmsmmcq ow cofiwExmse cmumwm co wmcoammm .m m_nmp 37 Anmzcfipcouv m.¢_ m.m m.m m.o mm. m.m m.m m.m m._ m.F m.o o.o N... aoeodufio m¢.¢ smgmpam: m.o_ m.m <.m m.. we. m.“ m.n m.¢ m.~ m.“ m._ m.“ om._ + cwfimgz_w~mzpm m.m~ m.m_ o.o m.o m_. o.N m.m m.o m.o m.o o.o o.o mm.~ :__oc:~m~o:pm o.mp o.m_ n.¢ P._ «N. o.< m.m m.o o.m o.m m.o o.o om._ :_~ogs~o~o2pm m.m. o.m_ m.m o._ mm. m._ o._ m.o m.o m.o o.o o.o mm._ :__eca_o~mzpm <~.m ammo:_u m.m_ o.__ m.m “.0 .m. o.m m.m o.m m.m m.m m._ m.o me.« + sm~mpamz mn.m mo_~:mcmn m.m_ m.P_ ~.¢ m._ mm. m.~ o.m m.m m.m m.m m._ m.. mm.o + Em_muamz m<.¢ mu_~:m:mn e.m_ m.m ¢.¢ N.F _v. o.“ m.o o.m m.“ m.o m.. m._ m¢.< + Em~muaoz m.N¢ _.N_ ..e 0.. m_. o.o o.o o.o o.o o.o o.o o.o umpmmguca Auxv ch\mxv fimpok umN_m m* mt _¢ Dazm zuou zmou saga coco «Ho «Ho mpmm mmufiufiacm: -Lm>o flho 4Ho mange mambo mumeo uo~a\ mpcmom Ap :mwz mmcwpwm mucwspmmgh ..mmF c. _H cowpmuo_ be =_~aca~c~acpm co m=o_pmu_~aao mumwcam mucmmcmemwga op Meaganuau mcwfixufla uwuwmm ucm mowmz do mmcoamwm .m m_nmh 41 .mcmfimgsa coeeou unmou .mcmgcmzomn58~ :oeeoU "oboe .ummzqu poocumg uzmmm .pcwsaomcp memm mxmc up cam: ammc_pmm mucmEpmmgh ._mm_ =_ __ :o_pmoo~ um mucmmgmsmmga op mcmne=uzo :_~oca_m_mcgw do :o_umuw_aac mummgam a:_o_~m umummm can muwmz Lo mmcoammm .m wfinoh 42 apparently delayed earliness of fruit development compared to the ethalfluralin treatments. Watermelon Study A reduction in crop stand was observed in the 1.68 kg/ha ethalflur- alin treatment, but total fruit yield was not reduced from that obtained in the untreated control (Table 7), in fact, fruit yield from the 1.12 kg/ha treatment was higher than that from the controls. Acceptable weed control was provided by both ethalfluralin treatments. Summer Squash Study Control of redroot pigweed, common lambsquarters and common purslane was commercially acceptable with both rates of ethalfluralin while crop stand was not adversely effected (Table 8). There were no differences observed in any of the yield parameters taken at individual harvest dates. However, the season total mean yield for the 1.68 kg/ha ethalfluralin treatment was 19% higher than the untreated control. winter Squash Studies Similar results were obtained in separate studies with acorn and butternut type winter squash (Table 9). While commercially acceptable control of the major weed species present was obtained, there was no differences among treatments with regard to either crop stand or fruit yield. Pumpkin Study As was noted for the other studies conducted at location 11 in 1981, the degree of weed control obtained with the ethalfluralin treatments was commercially acceptable (Table 10). There were no observed differ- ences among the treatments in either pumpkin stand counts or in mean 43 .mcm.mcza :oesou "smog .mcmuccacmn58_ coegou "coco .ummzm.a goocum. "zaam .pcmEHngp memm when u..=a me.m mm..-uwm3 umc.mp:.ms mew: mpo.a ._< ..mm. .N acne co um..qam c..mc=...mzaw new uwp:m_a macaw a.om m. m2 m. m. m.. N.N .mo.o. om. o..m o.m N.NN m.m ..m o.m o.ON No.. c..ag=...mnpm N..m N.N m.mN ..m ..m m.m m..N N... =__ac=.._m;.u N.Nm N.N o.©N o.o o.o o.o N.NN umpamcpcz flax. ..ocv .m;\m¥. .o.a\ .3 .o.a\ Daou oboe zaNN .. amm:_pmm macwspmmgh ..mm. c. ._ co..muo. pm :..w.=...mcwm .0 mco.uou._aam mum..:m mucmmcmsmmca ow =o_memem3 amummm can mumwz .o mmcoamma .N m.nwh 44 .H 4444.444 4444444444 ..44. 4. .. 44.4444. 44 444444 444544 444444 4444.4 4. 4..44:.4.4444 44 444.444..444 4444444 444444444444 44444 44444444 4444 444 .444444 4443 .4 4.444 45 .444.44:4 445544 "4444 .444444444454. 445544 "4.44 .44434.4 4444444 "3444 .4444544444 44444 4444 "444 ..444444 444: 444.4544 "4. ..444444 4443 44 "44 ..44. .4. 4.44 44 44.4444 444.4 444. 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N... 4..444.4.4444 4.4.. 4.4. 4.4 4.4 4.4 4.4. 444444444 .44. ..44. ..44. .44.4.. 44.4. 44.4. 4.44 4.44 2444 ..<4 4.. 4444 44.4.4444 4.444 4.444 44.4. :44: :44: 44:4: .444 44.. .444 44. 44.4.4 4444.444 4444544444 ..44. 4. .. 44.4444. 44 44.44544 444444 4444.4 44 4..444.4.4444 44 444.444..444 444444444444 44444 44444444 4444 444 4442 .4. 4.444 47 fruit weight. Plots receiving the 1.68 kg/ha treatment produced more fruit and more weight per plot than did the untreated controls. Preemergence surface applications of ethalfluralin at 1.12 and 1.68 kg/ha provided efficacious control of common purslane, common lambs- quarters and redroot pigweed in all tests conducted at location 11 in 1981. Large crabgrass was controlled with the 1.25, 1.96 and 2.52 kg/ha rates of ethalfluralin applied as a preemergence surface treat- ment in the muskmelon study at location I in 1979. In summary, the use of clear plastic mulch appeared to improve the tolerance of transplanted muskmelons to preplant incorporated ethal- fluralin treatments. Direct seeded muskmelons exhibited adequate tolerance to preemergence applications of ethalfluralin at 1.12 and 1.68 kg/ha. 'Green Star' cucumbers were very tolerant to PRE surface applica- tions of ethalfluralin from 1.25 to 2.52 kg/ha on the sandy loam soil with 2.2% 0.M. Both cucumber cultivars exhibited 50-90% increase in yield in the ethalfluralin treatments compared to the untreated controls in the 1981 studies. Although watermelon stand counts were reduced in the 1.68 kg/ha ethalfluralin treatments at the same site, the total yields were not reduced from those of the untreated control. Pumpkin, summer squash and winter squash were tolerant to PRE surface applications of ethalfluralin at 1.12 and 1.68 kg/ha. Preemergence surface applications of ethalfluralin can be utilized for efficacious control of several weed species in cucurbit crops with a reasonable margin of safety. In addition, the use of clear plastic mulch can enhance growth of transplanted muskmelons and improve their tolerance to preplant incorporated ethalfluralin. 10. 11. 12. 13. 14. LITERATURE CITED Adeniji, A.A. and D.P. Coyne. 1981. Inheritance of resistance to trifluralin toxicity in Cucurbita moschata Poir. HortScience 16:774-775. Barrentine, W.L. and G.F. Warren. 1971. Differential phyto- toxicity of trifluralin and nitralin. Weed Sci. 19:31-37. Barrentine, W.L. and G.F. Warren. 1971. Shoot zone activity of trifluralin and nitralin. Weed Sci. 19:37-41. Boldt, P.F. and A.R. Putnam. 1980. Selectivity mechanisms for foliar applications of diclofop-methyl. I. Retention, absorption, translocation and volatility. Weed Sci. 28:474~477. Buchholz, Carl. 1965. Weed control under clear plastic mulch. Paper No. 542, Dept. of Veg. Crops, Cornell University, Ithaca, New York. 8 pp. Cialone, J.C. and F.D. Schalas. 1966. Combinations of herbicides and plastic mulch for weed control in muskmelon and cucumber. Proc. Northeast. Weed Control Conf. 20:76-80. Derr, J.F. and T.J. Monaco. 1982. Ethalfluralin acitivity in cucumber (Cucumis sativus). Weed Sci. 30:498-502. Gorske, S.F. 1980. Muskmelon weed control programs with plastic mulch. Proc. NCWCC 35:95. Gorske, S.F. 198D. Weed control in pickling cucumbers. Proc. NCWCC 35:94-95. Humphreys, W.H., D.A. Addison, R.D. Hicks, K.E. McNeil, J.C. Nicholson, L.B. Rowland, and H.L. Webster. 1978. Ethalfluralin for weed control in cucurbits. Proc. South. Weed Sci. Soc. 31: 159-166. Jacobson, R., A. Greenberger, J. Katan, M. Levi, and H. Alan. 1980. Control of Egytian Broomrape (Drobanche aegyptiaca) and other weeds by means of solar heating of soil by polyethylene mulching. Weed Sci. 28:312-316. Locascio, S.J. 1978. Weed control with ethalfluralin, oryzalin, and pendimethalin. Proc. South. Weed Sci. Soc. 31:152-158. Menges, R.M. and Simon Tamez. 1981. Response of cucumber (Cucumis sativus) to annual weeds and herbicides. Weed Sci. 29: 2 - . Monaco, T.J. and W.A. Skroch. 1980. A summary of ethalfluralin performance on cucurbits. Proc. South. Weed Sci. Soc. 33:71-80. 48 15. 16. 17. 18. - 49 Nuland, 0.5. and C. Boyes. 1968. Weed control and stand estab- lishment in pickling cucumbers at Lincoln, Nebraska in 1968. NCWCC Research Report. 25:28-29. Raboy, Victor and Herbert J. Hopen. 1982. Effectiveness of starch xanthide formulations of chloramben for weed control in pumpkin (Cucurbita moschata). Weed Sci. 30:169-174. Werner, G.M. and A.R. Putnam. 1908. Differential atrazine tolerance within cucumber (Cucumis sativus). Weed Sci. 28:142- 148. Williamson, S.W. and C.E. Beste. 1980. Soil residue of ethal- fluralin with cucumbers. Proc. Northeast. Weed Sci. Soc. 34:189- 194. CHAPTER 3 RESPONSE OF SELECTED CULTIVARS OF BEANS (Phaseolus vulgaris L.) AND CUCUMBERS (Cucumis sativus L.) TO SOIL APPLICATIONS OF ETHALFLURALIN ABSTRACT Greenhouse and incubator studies were initiated to determine if ethalfluralin (N-ethyl-N-(Z-methyl-2-propenyl)-2,6-dinitro-4-(tri- fluoromethyl)benzenamine) causes morphological aberrations in germin- ating bean or cucumber seedlings and whether there is differential bean and cucumber cultivar tolerance to ethalfluralin. Ethalfluralin caused gross radial enlargement of bean root tips, swelling of hypo- cotyls, and in 'Spartan Arrow' inhibition of hypocotyl unhooking. Inhibition of lateral root development, restriction of hypocotyl elongation and hypocotyl swelling were observed in cucumbers treated with ethalfluralin. 'Spartan Arrow' snap beans were the most sensitive of bean cultivars tested while 'Domino', a black turtle type bean, were very tolerant to ethalfluralin at 8.96 kg/ha. Visible injury ratings were found to be more indicative of ethalfluralin injury to beans than either shoot fresh or dry weights. The 'GP14A' and 'Tempo' cucumber cultivars were found to be tolerant to preplant incorporated treatments of ethalfluralin at 1.12 kg/ha while 'Market- more 70', 'Marketmore 76' and 'Calypso' cultivars were significantly reduced in both shoot fresh and dry weight production. 50 51 INTRODUCTION Members of the dinitroaniline class of herbicides often cause morphological abnormalities in germinating seedlings. Lignowski and Scott (8) reported that trifluralin (a,a,u-trifluoro-Z,6-dinitro-N,N- dipropyl-p;toluidine) inhibited root elongation and induced root tip swelling of corn (Zea_may§_L.) and wheat (Triticum aestivum L.). Schultz et a1. (14) also reported that trifluralin caused radial enlargement of the root tip of corn but found no effect upon germ- ination. Upadhyaya and Nooden (16) found that root applied oryzalin (3,5-dinitro-N4,Né-dipropylsulfanilamide) inhibited root elongation and caused swelling in the elongation zone. In another study (15), they found that several dinitroaniline herbicides induced root tip swelling in corn seedlings. Murray et a1. (10) found that dinitramine (N4,N“- diethyl-a,a,a—trifluoro-3,5-dinitrotoluene-2,4-diamine), profluralin (N-[cyclopropylmethylJ-a,a,a-trifluoro-Z,6-dinitro-N-propyl-p;toluidine) and trifluralin reduced both root and shoot growth in cotton (Gossypium hirsutum L.) and soybean (Glycine max L.). Barrentine and Warren (2) noted that trifluralin had a greater effect on the growth of soybean (Sorghum bicolor L. Moench) and cucumber (Cucumis sativus L.) shoots while nitralin (4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline) caused the greatest inhibition of root growth. They also reported that when trifluralin and nitralin were applied to cucumber hypocotyl hooks, hypocotyl swelling occurred, as well as a reduction in shoot height (3). Harvey (7) studied the relative toxicities of dinitro- aniline herbicides and found that the inhibition of root and shoot 52 growth varied among plant species tested and among herbicides. Murray et al. (11) investigated the effect of structural change on the activity of six dinitroaniline herbicides. They reported that the tolerance of several species of plants varied with structural changes in the herbicide molecule. For decades, plant breeders have routinely screened their breeding lines and progeny for superior disease resistance. More recently, the selection of genetic material for improved herbicide tolerance has become important. The differential in cultivar tolerance to a herb- icide can be significant, for example, certain cultivars of soybeans and wheat have been reported to be more tolerant to metribuzin (4-amino- 6-tert-bUtyl-3-(methylthio)-as-triazin-5(4H)-one) than others (6,9,13). Freedman (5) found several potato (Solanum tuberosum L.) cultivars with superior tolerance to metribuzin while Werner and Putnam (17) identi- fied a cucumber accession that tolerated 4 fold the rate of atrazine (2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine) that killed most other cucumber cultivars and accessions. Adeniji and Coyne (1) have proposed a mechanism for inheritance of resistance to trifluralin injury in squash (Cucurbita moschata Poir). In a limited screening trial, Derr and Monaco (4) found no difference in ethalfluralin tolerance among the 16 cucumber cultivars tested. In contrast, Nuland and Boyes (12) reported finding differential tolerance between cucumber cultivars 'Spartan Dawn' and 'SMR 58' to trifluralin and chloramben (3-amino-2,5-dichlorobenzoic acid). These studies were initiated to determine (a) if ethalfluralin causes similar morphological aberrations in cucumber and bean seedlings 53 that have been reported for other dinitroaniline herbicides in other crops, and (b) whether there is differential bean and cucumber cultivar tolerance to ethalfluralin. METHODS AND MATERIALS Effects of ethalfluralin on germinating beans. Germination tests were conducted by placing five bean (Phaseolus vulgaris L. cv Seafarer) seeds in a 10 cm diameter glass petri dish lined with one piece of Whatman #1 filter paper. The filter paper was moistened with 4.0 ml of water containing ethalfluralin at 0 or 100 ppm. The petri dishes were sealed and held in an incubator at 30 C for two days. Each treat- ment was replicated four times and the experiment was repeated four times. Two days after treatment, the germinated seedlings were examined for morphological variability between treatments and percent germination was recorded. Effects of ethalfluralin on germinating cucumbers. Cucumber (Cucumis sativus L. cv Green Star) germination tests were conducted in a manner similar to that described for beans except the concen- trations of ethalfluralin were 0, 3.51, 35.1, or 351 ppm. Morpholog- ical variability and percent germination was recorded 4 days after treatment. Differential tolerance studies: Cultural Practices. Ethalfluralin was applied to the surface of a greenhouse soil mix (1:1:1, v/v/v, sand: peat: soil), by passing flats under a conveyor type sprayer that delivered approximately 340 L/ha spray diluent. The treated soil was 54 removed from the flat, throughly mixed in a rolling type mixer, and then replaced into the flat. The flats were seeded and placed in a greenhouse maintained at 2814 C day and 20:4 C night. Supplemental lighting was provided by metal halide lamps with a 16 h photoperiod and an intensity of 842 Em‘ZS'I. All plants were watered overhead as necessary and fertilized every five days with a dilute complete fertilizer solution. The experiment was terminated 12 (beans) and 16 (cucumbers) days after treatment by taking phototoxicity ratings and cutting the shoots off at soil level for fresh weight determination. The shoots were oven dried at 50 C for 72 h and dry weights taken. Weight data for ethalfluralin treatments are presented as percent of control. A randomized complete block design with four replicates was used for each study. The bean and cucumber studies were both conducted twice during the spring of 1982. Bean study. For each bean cultivar tested (Table 1) 10 seeds were planted in 16 x 13 x 5 cm styrofoam flats containing soil treated with 0, 1.12, 2.24, 4.48, or 8.96 kg/ha ethalfluralin. The seeds were planted in two rows approximately 2 cm deep with 3 cm between seeds in a row and 6.5 cm between rows. All raings were made 12 days after treatment. Cucumber study. The cucumber cultivars tested (Table 4) were planted into 25.5 x 25.5 x 5 cm plastic flats with soil containing either 0 or 1.12 kg/ha ethalfluralin. Six seeds for each cultivars were planted in single rows with approximately 4.5 cm between seeds in a row and 4.3 cm between each of the six rows. All ratings were made 16 days after treatment. 55 RESULTS AND DISCUSSION Effects of ethalfluralin on germinating beans. After 2 days, there was no significant difference in percent germination between seeds in the 0 or 100 ppm ethalfluralin treatments. Visual examination of the seedlings treated with 100 ppm ethalfluralin (Figure 18) revealed a consistant swelling of the root tip and of the hypocotyl region immediately below the cotyledons compared to the control (Figure 1A). As a result of gross radial enlargement of the root tip, cracks developed in the epidermis and extended into the cortex of the root. The root swelling of Phaseolus vulgaris seedlings caused by ethalflur- alin in this study is consistant with reports by other investigators (8,10,15,14) that dinitroaniline herbicides induce root tip swelling in a wide range of plant species. Effects of ethalfluralin on germinating cucumbers. The percent germination of cucumber seeds treated with 0. 3.51, 35.1, or 351 ppm ethalfluralin was not different four days after treatment. Previous investigators (14) have shown that dinitroaniline herbicides, as a group, do not affect the germination of seeds. The results of this study indicate that ethalfluralin does not differ from other dinitro- aniline herbicides in this respect. Increasing concentrations of ethalfluralin had marked effects on lateral root development, shoot elongation, and cotyledon coloration of germinating cucumber seedlings (Figure 2). Germinating cucumber seedlings treated with 3.51 ppm ethalfluralin showed little or no inhibition of lateral root develop- ment. Lateral root development was severly restricted by 35.1 ppm and 56 Figure 1. Bean seedlings germinated in petri dish with ethalfluralin at 0 ppm (A) and 100 ppm (B). 57 1 2 3 o 4 5 6 I CENTIMETERS ' ' om: hpmurm In; " ' -. fr! 5‘ ’ .1 _ , ms.- - v .-4- . , . ‘ ‘ P'Vfl 'kl’ I . o"§3“i£;41’.7 1: (y, "r 0 1 2 3 4 5 6 1 CENTIMETERS a K ONEDECIMETEF 58 Figure 2. Cucumber seedlings germinated in petri dishes with ethalfluralin at 0 and 351 ppm (A), 0 and 35.1 ppm (B), and with 0 and 3.51 ppm (C). 3. 51 PP! mrwmu 60 usually absent with 351 ppm ethalfluralin. Hypocotyl elongation was noticeably restricted in seedlings germinated in the ethalfluralin treatments. The inhibition of elongation was accompanied by an in- crease in hypocotyl diameter. Inhibition of elongation increased as ethalfluralin rates increased, and at 351 ppm ethalfluralin, there was a 70% reduction in hypocotyl length compared to the control. Higher rates of ethalfluralin caused the cotyledons to become curled and to develop a much darker green coloration than the control. Differential bean cultivar tolerance study. Reductions in plant height, mass, or general plant vigor were all observed as injury symptoms on beans grown in treated soil. Additionally, inhibition of hypocotyl unhooking and extreme hypocotyl swelling was noted in the 'Spartan Arrow' cultivar treated with 8.96 kg/ha ethalfluralin (Figure 38). At 1.12 kg/ha, no visible injury occurred in any of the cultivars tested (Table 1). Only 'Neptune', 'Spartan Arrow', and 'Black Magic' exhibited slight symptoms of injury at 2.24 kg/ha. Though all cultivars showed injury symptoms at both the 4.48 and 8.96 kg/ha rates, 'Spartan Arrow' was severely injured, while 'Domino', 'Swan Valley', and 'Montcalm' showed only slight injury. 'Seafarer', 'Black Magic', and 'Neptune ' showed moderate injury at the 8.96 kg/ha rate. There was no significant difference among cultivars in either fresh weight or dry weight as a percent of untreated in the 1.12. 2.24, or 4.48 kg/ha ethalfluralin treatments (Table 2). At the 8.96 kg/ha rate there were significant weight reductions with some cultivars. On a fresh weight basis, 'Swan Valley', 'Montcalm', and 'Domino' cultivars showed little or no reduction in growth. Fresh weight of 'Spartan 61 Figure 3. 'Black Magic' (A), a tolerant bean cultivar and 'Spartan Arrow' (8), a susceptible cultivar germinated in soil with ethalfluralin incorporated at 0, 1.12, 2.24, 4.48 and 8.96 kg/ha (left to right). 62 63 Table 1. Phytotoxicity ratings on bean gultivars after preplant applications of ethalfluralin. Rate (kg/ha) Beanb Cultivar type 1.12 2.24 4.48 8.96 Seafarer N 0 0 1.38 4.25 Montcalm K 0 0 0.50 1.12 Black Magic 8 0 0.38 0.50 2.75 Swan Valley N 0 0 0.25 0.88 Domino 8 0 0 0.12 0.50 Neptune N 0 1.38 1.75 2.88 Spartan Arrow S 0 0.88 3.25 8.50 LSD (0.05) NS 0.46 1.35 1.23 aBean phytotoxicity ratings were on a 0-10 scale where 0: no effect on height, mass, or vigor and 10: complete death of plants. All ratings were made 12 days after treatment. The phytotoxicity ratings are averaged over two experiments. bN= Navy; K: Kidney; B= Black Turtle; S: Snap. 64 Table 2. Average dry weight of untreated beans and influence of ethalfluralin on shoot dry weight production as a percent of control.3 Ethalfluralin (kg/ha) 0 1.12 2.24 4.48 8.96 Shoot dry Cultivar wt (9) Shoot dry wt (% of control) Seafarer .166 105.6 105.6 95.4 83.4 Montcalm .299 100.0 90.8 85.8 87.4 Black Magic .191 95.4 92.1 94.8 85.3 Swan Valley .171 95.5 99.6 91.5 101.9 Domino .178 98.1 98.8 91.0 86.6 Neptune .176 86.9 84.0 84.6 80.3 Spartan Arrow .232 97.6 78.0 99.5 94.5 LSD (0.05) NS NS NS 13.5 aThe average shoot dry weights per plant, taken 12 days after planting, are averaged over two experiments. 65 Arrow' was inhibited significantly more (44%) than any of the other cultivars tested. An intermediate reduction in fresh weight was observed with 'Neptune', 'Black Magic', and 'Seafarer'. There was no reduction in dry weight with 'Swan Valley' even with the 8.96 kg/ha treatment. Although, 'Spartan Arrow' dry weight production appeared somewhat depressed, it was not significantly lower (5% level) than that of 'Swan Valley'. The dry weight production of all other cultivars tested was 14-20% lower than that of 'Swan Valley'. The correlation coefficients for bean phytotoxicity ratings, percent fresh weights and percent dry weights were calculated for each herbicide rate (Table 3). The correlation between the phytotoxicity rating and percent dry weight production was low at all rates tested. An example of this lack of correlation can be seen in data presented in Tables 1 and 2 and Figure 38 for 'Spartan Arrow' treated at 8.96 kg/ha. While extreme injury was observed in this treatment, the dry weight production was reduced only 5.5% from that of the control. The correlation between percent fresh weight and percent dry weight decreased as the rate of ethalfluralin and degree of visible injury increased. The correlation between the phytotoxicity ratings and percent fresh weight production increased with increasing rates of ethalfluralin and increasing visible injury to the seedlings. This study shows that dry weight production may be a poor indicator of ethalfluralin injury to bean seedlings and that fresh weight production is not as sensitive an indicator of injury as are visible ratings. This study demonstrates that a significant difference in tolerance to higher rates of ethalfluralin exists between Phaseolus vulgaris 66 Table 3. Correlation coefficients for percent fresh weight and phytotoxicity rating, percent dry weight and phytotoxicity rating and for percent dry weight and percent fresh weight of seven bean cultivars treated with ethalfluralin at 1.12, 2.24, 4.48 or 8.96 kg/ha.a b Variable Rate Phytotoxicity % Fresh (kg/ha) Variable Rating Wt. _(Corre1ation Coefficients)— 1.12 % Fresh Wt. -0.070 % Dry Wt. -0.143 0.892** 2.24 % Fresh Wt. -0.420 % Dry Wt. -0.360 0.849* 4.48 % Fresh Wt. -0.471 % Dry Wt. -0.138 0.788* 8.96 % Fresh Wt. -0.709 % Dry Wt. -0.126 0.627 6Correlation coefficients are calculated using data for two experiments. bThe % fresh and % dry weights are shoot weights expressed as % of untreated control. Significant at P<0.05(*) or P<0.01(**). 67 cultivars. Although all cultivars tested showed good tolerance to ethalfluralin at commercially used rates, increased sensitivity of 'Spartan Arrow' could be a concern under adverse growing conditions. Differential cucumber cultivar tolerance study. As was noted for beans, 3 reduction in plant height, mass or general plant vigor was also observed in cucumbers treated with preplant incorporated ethal- fluralin. There were no significant differences in phytotoxicity ratings among any of the cultivars tested, while all cultivars showed some ethalfluralin toxicity (Table 4). Differences were observed among dry shoot weights of treated cucumber cultivars. 'GP14A', 'Tempo' and 'National Pickling' showed the least reduction, while 'Marketmore 76', 'Marketmore 70' and 'Calypso' had the greatest reduction in fresh weight. 'GP14A' and 'Tempo' showed only slight symptoms of being inhibited by ethalfluralin, while 'Marketmore 70', 'Marketmore 76' and 'Calypso' were substantially inhibited. The dry weight production of 'GP14A', 'Earlipik' and 'Lemon' was least affected by ethalfluralin, while the 'Marketmore 76', 'Market- more 70' and 'Calypso' incurred substantial reductions in dry weight production. The correlation coefficient between percent fresh and percent dry weight was 0.803 which was significant at P<0.01. The correlation coefficients between phytotoxicity ratings and percent fresh or dry weight for all cultivars were -0.599 and -0.460 respectively, both of which were significant at P<0.01. This study shows that cucumbers do not exhibit good tolerance to incorporated ethalfluralin treatments. This study also suggests, based on the 68 Table 4. Phytotoxicity ratings and influence of ethalfluralin (1.12 kg/ha) on shoot dry weight production as a percent of control.a Dry Wt. Cultivar Rating (% of untreated) ABC Hybrid Improved Lucky Strike Setter Triplemech Bounty Chemset GP14A High Mark II MarketMore 76 Poinsett 76 Premier Score Spartan Wonder Sprint 440(n) Sprint 440(5) Tamor XP 1191 XP 1304 XP 1338 E 0210 E 0212 FM 4285 FX 4320 FX 4551 Gemini Green Star Marketmore 70 Pennant Raider Regal Slicemaster Tempo Karmon RS 78003 RS 78053 (continued) a o o o o o o o o o o o o o o o o o o o o o o o NOMb-sNmeD-bhxommmxommoooom»mimoo-hxoxomo-ammo NNNNNNNNQ’NNNNNNNNNwwNNNwNwwN-PNNNNNW O O I O O O O O O O I whuommmhmommaomaanaoomhwummoo-uowpmm 69 Table 4. (continued) Dry Wt. Cultivar Ratingb (% of untreated) RS 79031 2.9 76.7 R5 80022 2.0 83.1 County Fair 2.9 81.8 Double Yield Pickling 1.8 80.3 Lemon 1.9 93.5 Liberty 2.1 86.3 National Pickling 2.5 90.1 Patio Pick 2.2 84.1 Peppi 2.4 86.0 Saladin 2.2 77.7 Salty 2.2 88.7 Spartan Dawn 2.1 86.2 Wisconsin S.M.R. 58 2.5 84.3 Calypso 3.4 72.1 Carolina 3.1 84.4 Earlipik 14 1.9 94.3 Green Spear 14 2.2 86.7 Pikmaster (808) 3.0 80.2 Tri Spear 2 2 79.7 LSD (0.05) NS 11.8 aThe phytotoxicity ratings and average shoot weights, taken 16 days after planting, are averaged over two experiments. bCucumber phytotoxicity ratings were on a 0-10 scale where 0: no effect on height, mass or vigor and 10: complete death of plants. 70 percent fresh and dry weight data, that differential cucumber tolerances to ethalfluralin occur. These studies demonstrate that ethalfluralin induces morphological abnormalities similar to those reported for other dinitroaniline herbicides such as root tip swelling, hypocotyl swelling and inhibition of hypocotyl unhooking in beans and inhibition of lateral root develop— ment and hypocotyl swelling in cucumber. Inhibition of germination by ethalfluralin was not observed in either beans or cucumbers. All bean cultivars examined in the cultivar tolerance study showed good toler- ance to ethalfluralin at practical field rates (1.12 to 2.24 kg/ha) under the conditions of this study. However, at higher treatment rates the 'Spartan Arrow' and 'Seafarer' were severly injured while 'Domino', 'Swan Valley' and 'Montcalm' continued to exhibit good crop tolerance. Under adverse growing conditions, 'Spartan Arrow' and 'Seafarer' might be expected to incur herbicide injury from ethalfluralin at 2.24 kg/ha. Although no significant differences were found in the phytotoxicity ratings for cucumbers treated at 1.12 kg/ha ethalfluralin, significant differences among cultivars were noted in both percent fresh and dry weight. The fresh and dry weights of 'GP14A' and 'Tempo' were not reduced while 'Marketmore 70', 'Marketmore 76' and 'Calypso' had lowered fresh and dry weights. It is not clear from this study whether 'GP14A' and 'Tempo' could tolerate preplant incorporated ethalfluralin treatments under field conditions. These studies show that differential cultivar tolerance to ethalfluralin occurs in both beans and cucumbers. Based on these studies, it appears that bean and cucumber crop tolerance to ethalfluralin has a genetic basis and may well be subject to improvement by selective breeding. 10. 11. 12. 13. 14. LITERATURE CITED Adeniji, A.A. and D.P. Coyne. 1981. Inheritance of resistance to trifluralin toxicity in Cucurbita moschata Poir. HortScience 16:774-775. Barrentine, W.L. and G.F. Warren. 1971. Differential phytotoxicity' of trifluralin and nitralin. Weed Sci. 19:31-41. Barrentine, W.L. and G.F. Warren. 1971. Shoot zone activity of trifluralin and nitralin. Weed Sci. 19:37-41. Derr, J.F. and T.J. Monaco. 1982. Ethalfluralin activity in cucumber (Cucumis sativus). Weed Sci. 30:498-502. Freeman, J.A. 1982. The influence of weather on the response of potato cultivars to metribuzin. J. Amer. Soc. Hort. Sci. 107:189- 194. Hardcastle, W.S. 1979. Soybean (Glycine max) cultivar response to metribuzin in solution culture. weed SCT. 27:278-279. Harvey, R.G. 1973. Relative phytotoxicities of dinitroaniline herbicides. Weed Sci. 21:517-520. Lignowski, E.M. and E.G. Scott. 1971. Trifluralin and root growth. Plant and Cell Physiol. 12:701-708. Mangeot, B.L., F.E. Slife, and C.E. Rieck. 1979. Differential metabolism of metribuzin by two soybean (Glycine max) cultivars. Weed Sci. 27:267-269. Murray, D.S., J.E. Street, J.K. Soteres, and G.A. Buchanan. 1979. Growth inhibition of cotton (Gossypium hirsutum) and soybean (Glycine max) roots and shoots by three dinitroaniline herbicides. Weed Sci.'273336-342. Murray, D.S., P.W. Santelmann, and H.A.L. Greer. 1973. Differ- ential phytotoxicity of several dinitroaniline herbicides. Agron. J. 65:34-36. Nuland, 0.5. and C. Boyes. 1968. Weed control and stand establish- ment in pickling cucumbers at Lincoln, Nebraska in 1968. NCWCC Research Report 25:28-29. Runyan, T.J., W.K. McNeil, and T.F. Peeper. 1982. Differential tolerance of wheat (Triticum aestivum) cultivars to metribuzin. Weed Sci. 30:94-97. Schultz, D.P., H.H. Funderburk, Jr., and N.S. Negi. 1968. Effect of trifluralin on growth, morphology, and nucleic acid synthesis. Plant Physiol. 43:265-273. 71 15. 16. 17. 72 Upadhyaya, M.K. and L.D. Nooden. 1977. Mode of dinitroaniline herbicide action I. Analysis of the colchicine-like effects of dinitroaniline herbicides. Plant and Cell Physiol. 18:1319-1330. Upadhyaya, M.K. and L.D. Nooden. 1978. Relationship between the induction of swelling and the inhibition of elongation caused by oryzalin and colchicine in corn roots. Plant and Cell Physiol. 19:133-138. Werner, G.M. and A.R. Putnam. 1980. Differential atrazine tolerance within cucumber (Cucumis sativus). Weed Sci. 28:142- 148. Chapter 4 ABSORPTION AND TRANSLOCATION OF 14C-ETHALFLURALIN IN CUCUMBER (Cucumis sativus L. cv Green Star), BEAN (Phaseolus vulgaris L. cv Seafarer) AND PEA (Pisum sativum L. cv Sparkle) ABSTRACT Field and greenhouse studies were initiated to determine absorption and translocation characteristics of 14C-ethalfluralin (N-ethyl-N-(Z- methyl-2-propeny1)-2,6-dinitro-4-(trifluoromethyl)benzenamine) in vegetable crops. In field studies, cucumbers treated with 1.68 or 3.36 kg/ha preemergence surface applications of 14C-ethalfluralin accumu- lated significantly more 14C in leaves than in petioles, stems or fruits. Beans and peas treated with preplant incorporated 14C-ethal- fluralin were found to contain 14C in the plant parts tested. In greenhouse studies, 14C-ethalfluralin vapor was found to be absorbed by both cucumber seedling stems and cotyledon tissue. Both bean and cucumber seedlings were found to absorb 14C-ethalfluralin from a nutrient solution and translocated 14C into all plant parts. Both cucumber and bean absorbed 14C-ethalfluralin topically applied to the stem and translocated 14C acropetally while only limited basipital translocation occurred. Although both cucumber and bean cotyledons absorbed 14C-ethalfluralin, very little 14C moved out of the treated tissue. 73 74 INTRODUCTION Few herbicides are available which selectively control broad- leaved weeds and grasses in cucurbit crops. This is because cucurbits are sensitive crops and exhibit only moderate tolerance to the few herbicides currently registered. Recent work has demonstrated good weed control in cucurbit crops with the dinitroaniline herbicide ethalfluralin (11,12,18). However, crop tolerance and mechanism of selectivity in cucurbit crops to ethalfluralin are not well understood. Parker (10) demonstrated that chlorpropham (isopropyl m-chloro- carbanilate), dichlobenil (2,6-dichlorobenzonitri1e) and trifluralin (a,a,a,-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) can exert their herbicidal action through direct uptake by the shoot of Sudax (Sorghum vulgare x sudanense), but root uptake appeared to be much more effective. Barrentine and Warren (1) reported that nitralin (4-(methyl- sulfonyl)-2,6-dintro-N,N-dipropylaniline) was more toxic to cucumber roots than trifluralin. However, trifluralin applied to the cucumber shoot zone was more effective in reducing shoot weight than was nitra- 14 lin. In another study (2), they reported that more C-trifluralin and 14C-nitralin were taken up in the hypocotyl hook region of cucumber seedlings than from cotyledons or the hypocotyl region below the hypo- cotyl hook. Derr and Monaco (3) found that both root and shoot uptake of ethalfluralin occurs in cucumbers, but that shoot exposure was less injurious to cucumber growth than root exposure. The relative toxicities of dinitroaniline herbicides vary widely 75 and are species dependent (1,8). Jordan et al. (8) reported that the relative vapor toxicities of several dinitroaniline herbicides to Japanese millet (Echinochloa crus-galli (Roxb.) Wight) generally correlated with their vapor pressures. One exception noted by Jordan was that dinitramine (N‘,N‘diethyl-a,u,a-trifluoro-3,5-dinitrotoluene- 2,4-diamine) though not as volatile as other compounds, was highly toxic to Japanese millet shoots. Other investigators have also confirmed vapor activity of dinitroaniline herbicides (4,6,9,14,16). Savage (13) found that ethalfluralin volatility from soil approximated that of trifluralin. Since the entire plant may be exposed to these volatile herbicides through vapor contact, each plant part is a possible site of herbicide uptake. 0nly limited translocation of dinitroaniline herbicides within plants has been reported to occur. Little 14 C-oryzalin (3,5-dinitro- N“,N“-dipropy1-su1fanilamide) was found to move from corn (Z22.E21§.L-) roots to shoots (17). Jacques and Harvey (7) observed some root to shoot translocation to benefin (N-butyl-N-ethyl-a,a,a~trifluoro-2,6- dinitro-p-toluidine), dinitramine, fluchloralin (N,(chloroethyl)-2,6- dinitro-N-propyl-4-(trifluoro methyl)aniline), profluralin (N-(cyclo- propyl methyl)-a,a,a-trifluoro-2,6-dinitro-N-propyl-p-toluidine) and trifluralin in peas (Pisum sativum L.), but no shoot to root transport was detected. In a microradioautographic study, Strang and Rogers (15) found that radioactivity from 14C-trifluralin was retained primarily on the surface of the treated cotton (Gossypium hirsutum L.) and soybean (Glycine max (L.) Merr.) roots. Radioactivity was noted in the walls of xylem vessels and cortical cells in roots of both cotton 76 and soybeans. Radioactivity was also noted in the protoxylem of the cotton stem. The purpose of this study was to assess the degree of ethalfluralin uptake by various parts of cucumber and bean plants, the subsequent translocation of the absorbed herbicide, and to determine if these factors influence selectivity in these crops. METHODS AND MATERIALS Field Study Cultural practices. A field site was selected at the Michigan State University Horticultural Research Farm, East Lansing, Michigan on a Spinks loamy sand soil (Appendix Table A1). Four galvanized metal culverts 914 cm in diameter and 610 cm in length were placed vertically into the soil a maximum depth of 457 cm with a minimum disturbance of 14C- the naturally occurring soil profiles. Uniformly ring labeled ethalfluralin with a specific activity of 2.78 uci/umole was amended with technical grade (98.6%) ethalfluralin and dissolved in acetone to produce the following 14C-ethalfluralin solutions: (A) a 250 ml solution of 110.4 mg (0.753 uCI/uMOle), (B) a 250 ml solution of 220.9 mg (0.376 uci/pmole), (C) a 50 ml solution of 110.4 mg (0.753 uci/umole), and (D) a 50 ml solution of 220.9 mg (0.376 uci/umole) ethalfluralin. Analysis by TLC indicated the purity of the 14 97%. C-ethalfluralin to be greater than Cucumber. Cucumber seeds were planted at a depth of 2.5 cm in each 14 of two culverts on July 17, 1980. The C-ethalfluralin solutions C 77 and D were each throughly mixed with 900 cm3 soil samples which were removed from the seeded culverts. Each soil sample, after treating, was evenly distributed over the soil surface within the individual 14C-ethal - culverts on July 18, 1980. These two treatments resulted in fluralin being applied at rates of 1.68 and 3.36 kg/ha respectively. Immediately after the treated soil was applied to the sites, each cul- vert was irrigated with approximately 1.0 cm of water. The individual sites were hand irrigated as required throughout the growing season. Plants in both treatments were harvested at soil level 56 days after treatment. Plants were throughly cleaned of surface soil by rinsing with water and scrubbing with a brush as required. Individual plants were seperated into leaves, petioles, stems and fruit, placed into plastic bags, frozen and stored at -25 C. Beans and peas. On July 17, 1980, the top 6.4 cm layer of soil was removed from an untreated culvert and placed into a metal drum equipped with a tight fitting cover. Solution A was throughly mixed with the soil in the drum by rolling the drum. The treated soil was replaced into the culvert and evenly distributed. Solution 3 was applied to the soil from a second culvert in a similar manner. These two treatments resulted in 14C-ethalfluralin being applied at rates of 1.68 and 3.36 kg/ha respectively. Beans and peas were planted at a depth of 2.5 cm in each culvert and then irrigated with approximately 1.0 cm of water. The individual sites were sprinkle irrigated to prevent stress throughout the growing season. Pea plants in both the 1.68 and 3.36 kg/ha treatments were harvested at soil level 49 days after treatment. Plants were cleaned 78 of surface soil by rinsing with water. Plants were separated into leaves, stems, pods and seeds with each type of plant part being frozen, partially lyophilized and allowed to dry to air dryness at room temperature. Bean plants in the 1.68 kg/ha treatments were harvested both two and four weeks after treatment, throughly cleaned of surface soil, and prepared for autoradiography. Mature bean plants in both the 1.68 and 3.36 kg/ha treatments were harvested at soil level 98 days after treatment. Plants were cleaned of surface soil by scrubbing with a brush. Pods and seeds were seperated from stem material and dried for radioassay. Radioassaygand Statistical Analysis. Ten cucumber fruits from both the 1.68 and 3.36 kg/ha treatments were individually homogenized in a Sorvall Omni-Mixer at high speed. Plant homogenates were evenly slurried into aluminum pans and frozen on dry ice. For each fruit sample, 10 sub-samples of the frozen homogenate were taken for com- bustion. For leaves, stems and petioles, five sub-samples were taken from each of five plants for combustion. Representative bean and pea samples were also taken from the collected plant material for combustion. Samples (300 mg) were combusted in an 0X-200 Harvey Biological Oxider flow rate of 300 cm3/min for 4 min. 14CO was 2 2 absorbed in 15 m1 2:1 (v/v) Permaflour V liquid scintillation counting at 900 C with an 0 solution: Carbosorb II C02 absorbant (Packard) and radioassayed by liquid scintillation spectrometry. Each sample was counted for 100 min or 4,000 counts, whichever occurred first. Counts for each sample were corrected for quenching by external standard channels ratio, 79 background and oxidation efficiency. The disintegrations per min (DPM) for each sample and sub-sample was converted to DPM/g basis and the average DPM/g for each sample was calculated. All quantitative data for 14C—residues were calculated as 14C-ethalfluralin equivalents. Data were subjected to ANOV and plant part comparisons were achieved with paired t-tests. Greenhouse Studies Vapor uptake study. Individual cucumber seedlings were germinated in styrofoam cups containing a greenhouse soil mix (1:1:1, v/v/v, sand: peatzsoil). One day after the cotyledons were fully expanded, a glass cover slip with 228,000 DPM (2.78 pCI/meIe) 14C-ethalfluralin was positioned horizontally 1 cm below the cotyledon and 0.5 cm from the stem. The plants were maintained in a greenhouse at 28:4 C day and 20:4 C night with 50-70% R.H. for 24 h. Supplemental lighting was provided by metal halide lamps with a 16 h photo period. At 6 and 24 h after treatment, plants were harvested by washing soil from the root system and either dividing the plants into roots, stem, adjacent and opposite cotyledons for combustion or prepared for auto- radiography. Samples were combusted as described previously and the 14C quantitated for each plant part. The 14C-residue remaining on the cover slip was determined by placing the cover slip in a scintillation vial with 15 ml of ACS (Amersham), a prepared liquid scintillation cocktail, and quantitating by liquid scintillation spectrometry. Four replications of one plant for each treatment were employed. The percent 14C-ethalfluralin volitilized, percent 14C-vapor absorbed and distribution of 14C in root, stem, untreated cotyledon and treated 80 cotyledon was calculated. All data represent the means of two experiments. Root uptake study. Bean and cucumber seeds were germinated in vermiculite moistened with one-half strength Hoagland's solution (5). TWo days after the unhooking of the hypocotyls, the vermiculite was washed from the plant roots. TWo bean or cucumber plants were suspend- ed in a 100 ml glass beaker covered with aluminum foil and containing 60 ml of one-half strength Hoagland's solution (5). The beakers were aerated by bubbling air through the nutrient solution for 1 min every 30 min and the nutrient solution was replenished as needed throughout the experiment. After an acclimation period of 24 h, a 3 p1 aliquot of an acetone solution containing 666,000 DPM of 14C-ethalfluralin (2.78 uci/umole) was added to the nutrient solution of each beaker. A 1 cm layer of activated charcoal was then placed on top of the foam disk used to suspend the plants to adsorb volatilized 14C-ethalfluralin. This study was maintained in a greenhouse under conditions previously described. Plants were harvested 2, 6, 24 or 48 h after treatment by removing the plants from the treated nutrient solution and agitating the roots in 100 ml of one-half strength Hoagland's solution for 1 min. The plants were either prepared for autoradiography or divided into roots, stems, cotyledons and leaves all of which were stored at -26 C for analysis. The plant samples were combusted as previously described and the 14C quantitated by plant part. Three replications of two 14 plants for each treatment were employed. The total C absorbed by each plant and the percent distribution of 14C in each plant part was 81 calculated. All data are presented as the means of two experiments. Stem and cotyledon uptake studies. Beans and cucumber seeds were germinated in styrofoam cups containing a greenhouse soil mix (previously described). Two days after hypocotyl unhooking a 3 ul aliquot of methanol containing 252,000 DPM of 14'C-ethalfluralin (2.78 ”cl/umOIe) was applied in a 1 cm band around the seedling stem in the region 1 cm to 2 cm below the cotyledons. The surface area treated was 1 cm2 on the the bean stem and 0.6 cm2 on the cucumber stem. The cotyledons of another series of plants were treated one day after hypocotyl unhooking with 275,000 DPM of 14C-ethalfluralin (2.78 “cl/umole) applied evenly over the lower surface of one bean cotyledon or over the end 1 cm length of the upper surface of one cucumber cotyledon. The treated bean and cucumber cotyledon surface areas were ca 1 and 0.8 cm2 respectively. The study was maintained in a greenhouse under conditions previously described. Plants receiving stem applications of 14C-ethalfluralin were harvested at soil level 2, 4, 6 and 8 h after treatment and prepared for microautoradiography. Additional plants receiving stem treatments and plants receiving cotyledon treatments were harvested 6, 24 and 96 h after treatment by washing the soil from the roots with water and rinsing the treated area with 20 ml methanol. The plants were either prepared for autoradiography or divided into roots, stem, cotyledon and leaves which were stored at -26 C until combusted. The plant samples were combusted as previously described and the 14C quantitated by plant part. Four replications of one plant for each treatment were employed. The total 14C absorbed by each plant and the percent 82 distribution of 14C in each plant part was calculated. All data presented are the means of two experiments. 14C-Extraction and Characterization Study. Cucumbers and beans were germinated, treated, harvested and stored as described for the root uptake study. Roots, stems and cotyledons from two plants at each exposure time were homogenized and extracted with 80 % methanol (CH30H) (20 ml). The extract was filtered through 540 Whatman paper and the methanol removed by evaporation under vacuum at 35 C. The aqueous extract was partitioned with methylene chloride (CH2C12) (4 X 10 ml). The pooled methylene chloride phase was reduced in volume under vacuum at 35 C to 1.0 ml. The aqueous fraction and a 0.1 m1 aliquot of the methylene chloride fraction were individually assayed for radioactivity by liquid scintillation spectrometry using 15 ml ACS (Amersham) scintillation solution. The filter paper and methanol insoluble residue was combusted and radioassayed as described previously. A single study consisting of two plants for each treatment was employed. The total 14C absorbed by each set of plants and the percent distribution of 14C in each fraction for each part was determined. RESULTS AND DISCUSSION Field Study Cucumbers. More 14C accumulated in cucumber leaves at both treatment rates than in petioles, stems and fruits which all contained similar levels of 14C (Table 1). Leaves and petioles con- tained 1.8 to 2.4 fold more 14C in the 3.36 kg/ha than the 1.68 kg/ha 83 Table 1. 14C-residue in cucumber tissue following preemergence soil applications of 14C-ethalfluralin at 1.68 and 3.36 kg/ha. Mean 14C-residue Plant Rate (kg/ha) Part 1.68 3.36 (PPM) Leaf .164a .298a* Petiole .017b .041b* Stem .026b .041b Fruit .017b .017b 14 Mean C-residue calculated on fresh weight of plant material. Means within a column followed by the same letter are not significantly different (P<0.05, t-test). *Significantly different from 1.68 kg/ha treatment (P<0.05, t-test). 84 treatment while 14C detected in both stems and fruits were similar to each other at both treatment rates. Cucumber leaves appear to be a sink for absorbed 14'C-ethalfluralin or metabolites and fruit, though actively growing, do not accumulate appreciable amounts of 14C. 14C accumulated in both leaves and petioles approximately 14C doubled with a 2 fold increase in -ethalf1uralin application. Beans and peas. At both rates of 14'C-ethalfluralin, 3 to 4 times as much 14'12 accumulated in bean stems than pods (Table 2). Signifi- cantly less 14C was found in seeds than either pods or stems. Stems, pods and seeds in the 3.36 kg/ha treatment contained more than twice as much 14C than the comparable plant part in the 1.68 kg/ha treat- ment. The autoradiograph of a bean plant after 2 weeks soil exposure to 14C-ethalfluralin shows 14C is distributed in all plant parts with the highest concentrations being in the roots and vascular system (Figure 1). A comparable autoradiograph after 4 weeks soil exposure shows 14C is distributed in new leaf and stem tissue while 14C also continues to persist in the vascular system of the oldest leaves (Figure 2). It appears that 14C-ethalfluralin is absorbed by bean plants and parent compound and/or metabolites are translocated to the leaves and largely immobilized in the vascular system. The 3.36 kg/ha 14C-ethalfluralin treatment was extremely phyto- toxic to peas. Only 10% of the pea seedlings emerged, while those that did emerge were severely stunted compared to untreated guard plants. Although pea emergence was not inhibited in the 1.68 kg/ha treatment, plants were noticeably stunted. Leaves from peas treated with 1.68 kg/ha 14C-ethalfluralin contained nearly twice as much 85 Table 2. 14C-residue in beans and peas following pre-plant incorporated treatments of 14C-ethalfluralin at 1.68 and 3.36 kg/ha.a Beans IEEEE Plant Rate (kg/ha) Rate (kg/ha) Part 1.68 3.36 1.68 3.36 No. Samples/mean Leaf - - 6 5 Stem 9 9 6 5 Pod 20 20 6 - Seed 20 20 6 - Mean 14C-residue (PPM)b Leaf - - 3.958a 7.151a Stem 3.306a 10.420a 2.157b 6.443a Pod 1.053b 2.749b 0.383c - Seed 0.053c 0.126c 0.142c - aMean 14C-residue calculated on air dry weight of beans and fresh weight of peas. bMeans within a column followed by the same letter are not signifi- cantly different; means are significantly different between rates for each plant part tested (P<0.05, t-test). Figure 1. Figure 2. Figure 3. 86 Distribution of radioactivity in a bean plant 2 weeks after treatment with soil applied 14C-ethalfluralin. The plant specimen is on the left and the autoradio- graph on the right. Distribution of radioactivity in a bean plant 4 weeks after treatment with soil applied 14C-ethalfluralin. The plant specimen is on the left and the autoradio- graph on the right. Distribution of radioactivity in a cucumber seedling after 6 hours exposure to 14C-ethalfluralin vapor. The cotyledon adjacent to treated glass plate is on the left. The plant specimen is on the left and the autoradiograph on the right. 88 14C than stems from the same treatment. The 14C in pods and seeds were similar to each other but 5 to 15 times less than stem 14C levels. Leaves and stems of peas in the 3.36 kg/ha treatment contained more 14C than the same plant parts from the 1.68 kg/ha treatment but were not different from each other. Greenhouse Studies 14 Vapor uptake study. C-ethalfluralin readily volatilized from the surface of the glass disc with 81.1% of the applied material being volatilized after 24 h (Table 3). The total 14C-ethalfluralin absorbed by the cucumber seedlings was 0.4 and 0.6% after 6 and 24 h exposures respectively. The autoradiograph of a seedling after 6 h exposure shows that 14C-vapor was absorbed by the stem region adjacent to and above the level of the glass disc (Figure 3). Although significantly more 14C-ethalfluralin volatilized after 24 h than 6 h the percent 14 C detected in the adjacent cotyledons and stems did not differ from that found after 6 h exposure. The adjacent cotyledons contained slightly more 14C than the opposite cotyledons after 6 h exposure, but this difference did not persist until 24 h after exposure. More 14C was detected in the opposite cotyledons after 24 h exposure as compared to 6 h exposure. The data suggests mobility of 14C from the treated cotyledon to the untreated cotyledon as well as acropetal movement of 14C from the stem to the untreated cotyledon. More 14C was observed in roots after 24 h than at 6 h which suggests basipital translocation of 14C-ethalfluralin does occur to a limited degree. Root uptake study. The percent of absorbed 14C detected in cucumber roots decreased while the 14C observed in cotyledons increased at each sampling period (Table 4). The autoradiograph of a cucumber 89 Table 3. Volatilization and absorption of 14 cucumber seedlings.a C-ethalfluralin by Exposure Time 14c Distribution 6‘h 24 h % Volatilized 74.6 81.1* Vapor absorbed 0.4 0.6 —-% of absorbed— Adjacent cotyledon 43.5 40.2 Opposite cotyledon 29.2 38.6* Stem 27.2 20.7 Root 0.1 0.5* LSD (0.05) 8.0 9.1 aMeans are average for two experiments. *Significantly different from 6 h treatment (P<0.05, t-test). 9O Table 4. Distribution of 14C in cucumber and bean seedlings following exposure of roots to 14C-ethalfluralin.a Exposure 14C Distribution Total 14C Plant Time Root Stem Cotyledon Leaf absorbed (h) % (DPM/Plant) Cucumber 2 90.63 6.15 3.22 - 17921 6 82.85 10.93 6.22 - 13362 24 76.38 10.12 13.48 - 11585 48 67.52 11.58 20.87 - 14413 LSD(0.05) 4.42 2.68 2.90 N.S. Bean 2 96.85 2.63 0.00 0.48 41492 6 89.20 7.13 0.08 3.58 28550 24 80.27 11.72 0.33 7.67 22863 48 79.72 9.45 0.37 10.43 28047 LSD(0.05) 3.08 1.90 0.16 1.72 7418 aMeans are average for two experiments. 91 14 seedling after 24 h root exposure to C-ethalfluralin indicate that 14 the C in the cotyledons is concentrated in the vascular system (Figure 5A). A similar autoradiograph of a bean seedling also shows a 14 concentration of C in the vascular system of its leaves (Figure 4A). 14 The percent C found in cucumber stems remained relatively constant after 6 h. 14 The percent C observed in bean roots decreased at the 6 h and 24 h exposure intervals after which it remained similar until the 48 h 14 period. The percent C in bean stems increased with each exposure period until 24 h exposure, after which the level decreased slightly. 14 Only .37% of the total absorbed C was observed in the bean cotyledons 14 48 h after root exposure. The percent C detected in bean leaves increased at each exposure time until at 48 h, 10.43% of the total 14C was observed in the leaves. absorbed These data show that 14C-ethalfluralin is absorbed by the roots of cucumber and bean seedlings and that substantial 14C-material is translocated to the cotyledons of cucumbers and the leaves of beans. The autoradiographs indicate that ethalfluralin or metabolites move readily in the vascular system of the plants. Stem and cotyledon uptake study. Less than 1% of the total 14C- ethalfluralin absorbed was translocated to the roots of either cucumber or bean seedlings after stem exposure (Table 5). After 96 h exposure, 40.04% of the absorbed 14C-material was detected in the cotyledons of cucumber seedlings. In contrast, bean cotyledons contained only 4.25% and leaves 12.02% of the absorbed 14C. Absorption and translocation of 14C-material was much more rapid in cucumbers than in beans after stem Figure 4. 92 Distribution of radioactivity in bean seedlings 24 h 14C-ethalfluralin to (A) the root after treatment with system, (B) the stem and (C) a single cotyledon. The plant specimen is on the left and the corresponding autoradiograph on the right. 93 Figure 5. 94 Distribution of radioactivity in cucumber seedlings 14c-etnalfluralin to (A) 24 h after treatment with the root system, (B) the stem and (C) a single cotyledon. The plant specimen is on the left and the corresponding autoradiograph on the right. 95 96 Table 5. Distribution of 14 stem exposure to 1 C in cucumber and bean seedlings following 4C-ethalfluralin.a Exposure 14C Distribution Total 14C Plant Time Root Stem Cotyledon Leaf absorbed (h) % (DPM/Plant) Cucumber 6 .34 83.60 16.05 - 27786 24 .85 63.71 35.45 - 29280 96 .78 59.19 40.04 - 30947 LSD(0.05) N.S. 5.53 5.76 N.S. Bean 6 .10 96.64 1.46 1.80 14871 24 .35 89.46 2.45 7.74 22313 96 .81 82.91 4.25 12.02 33402 LSD(0.05) .17 1.34 1.07 1.12 5447 aMeans are average for two experiments. 97 exposure to 14C-ethalfluralin. Though a portion of the 14C found in the cucumber cotyledons and bean leaves may have resulted from vapor absorption, the autoradiographs of cucumbers and beans receiving stem treatments show a concentration of 14C in the vascular system indicating translocation of 14C (Figure 4B and 5B). Microradiographs of cucumber stem tissue from the region above the site of 14C-ethalfluralin application shows 14C-residues to be prominent in xylem tissue 6 h post treatment (Figure 6A and 68). Similarly, 14C-residue was observed in xylem tissue below the site of application though not as concentrated (Figure 6C). In a cucumber leaf cross-section, 14C-residue was again found to be concentrated in xylem tissue (Figure 6D). 14C-residue was concentrated in the intercellular spaces near the epidermis and in xylem tissue of bean stem cross-sections taken above the application site at 8 h post treatment (Figure 6E and 6F). After a 96 h exposure of cotyledons to 14“(S-ethalfluralin, 97.5% of the absorbed 14C was located in the treated cucumber cotyledons (Table 6). Both the data and the autoradiographs indicate that very little movement of 14C occurred out of treated cucumber cotyledons (Figure 5C). The 14C absorbed by bean cotyledons was somewhat more mobile with some movement evident into the stem and leaves (Figure 4C). 14C-Extraction and Characterization Study. The percent absorbed 14C detected in the methanol insoluble fraction increased in both cucumber and bean with exposure time (Appendix Table A2 and A3 and Table 7). The percent 14C observed in the methylene chloride fraction of bean extract was maximum (82.0 %) after 2 h exposure then decreased with time. The percent 14C in the methylene chloride fraction of Figure 6. 98 Microradiographs of cucumber and bean seedlings 14c-ethal- following topical stem applications of fluralin: (A) cucumber stem above application zone 6 h post treatment (X 300); (B) cucumber stem vascular tissue above application zone 6 h post treatment (X 300); (C) cucumber stem vascular tissue below application zone 6 h post treatment (X 875); (D) cucumber leaf vascular tissue 8 h post treatment (X 300); (E) bean stem tissue near epidermis above treatment zone 8 h post treatment (X 300); (F) bean stem vascular tissue above treatment zone 8 h post treatment (X 300). 100 Table 6. Distribution of 14C in cucumber and bean seedlings following cotyledon exposure to C-ethalfluralin.a 14c Distribution Exposure Untreated Treated Total 14C Plant Time Root Stem Cotyledon Cotyledon Leaf Absorbed (h) % (DPM/Plant) Cucumber 6 .09 .88 2.85 96.24 - 19370 24 .10 .35 2.24 97.30 - 29087 96 .21 ..36 1.76 97.50 .16 44024 LSD(0.05) .04 N.S. N.S. N.S. 6998 Bean 6 .02 1.85 1.00 93.76 3.36 18470 24 .02 1.14 0.52 96.88 1.44 39418 96 .03 2.04 0.88 94.20 2.55 44369 LSD(0.05) N.S. N.S. N.S. 1.90 N.S. 14052 aMeans are average for two experiments. 101 Table 7. Extraction and phase separation of radioactivity in cucumbers and beans after 2, 6, 24 or 48 hr root exposure to C-ethalfluralin. Recovered Radioactivity Exposure CHZCI2 Water CH30H Time Plant Phase Phase Insoluble (% of Total) 2 h Cucumber 52.4 43.1 4.5 Bean 82.0 10.3 7.7 6 h Cucumber 53.3 33.2 13.5 Bean 53.6 23.8 22.6 24 h Cucumber 31.1 31.3 37.6 Bean 25.1 28.2 46.7 48 h Cucumber 21.9 34.7 43.4 Bean 21.5 27.5 51.0 102 cucumber extract decreased after 6 h exposure. After 2 h, the percentage of 14C detected in the water soluble fraction of cucumber extract was four times greater than bean extract. For each treatment time, a higher percentage of 14C was found in the water soluble fraction of cucumber than bean while the reverse was true of the methanol insoluble fraction. Cucumbers, beans and peas absorbed 14C-ethalfluralin under field growing conditions and accumulated 14C in both leaf and stem tissue. Neither cucumber fruit nor bean seeds accumulated appreciable amounts of 14C in the field study. Nearly 3 times as much 14C was detected in pea seeds than bean seeds after the 1.68 kg/ha treatment. The low tolerance observed in peas to ethalfluralin may be related in part to increased shoot exposure to ethalfluralin due to the slower hypogeous germination of the peas as compared to the rapid epigeous germination of beans. The vapor uptake study demonstrated that 14C-ethalfluralin vapor is absorbed by both cucumber stems and cotyledons. The root uptake study confirms that ethalfluralin is readily absorbed from a nutrient solution by both cucumber and bean roots and readily translocated to cotyledonary leaves and leaves respectively. The disappearance of 14C from the roots of both cucumber and beans in the root uptake studies was possibly due to transport of 14C-material out of the root system or a sorption-desorption process between the roots and the nutrient solution. Root absorbed 14C-ethalfluralin was rapidly transformed into a water soluble compound in both cucumber and bean. This conversion to a water soluble material most likely 103 preceded the xylem loading and extensive translocation previously described. In both cucumber and bean, the 14 C-residue was gradually converted into a methanol insoluble form. It is reasonable to suspect that ethalfluralin vapors in the soil would also be absorbed by cucumber and bean roots. Stems of cucumber and bean seedlings did absorb topically applied ethalfluralin and subsequently translocated the absorbed 14C acropetally into the leaves. Both cucumbers and beans absorbed 14C-ethalfluralin applied to the cotyledons but little translocation of the absorbed material occurred. Since cotyledons, stems and roots are sites of ethalfluralin absorption, any condition which impedes growth of these plant parts out of the soil herbicide zone may result in subsequent herbicide injury. 10. 11. 12. 13. 14. LITERATURE CITED Barrentine, W.L. and G.F. Warren. 1971. Differential phyto- toxicity of trifluralin and nitralin. Weed Sci. 19:31-37. Barrentine, W.L. and G.F. Warren. 1971. Shoot zone activity of trifluralin and nitralin. Weed Sci. 19:37-41. Derr, J.F. and T.J. Monaco. 1982. Ethalfluralin activity in cucumber (Cucumis sativus). Weed Sci. 30:498-502. Harvey, R.G. 1974. Soil adsorption and volatility of dintro- aniline herbicides. Weed Sci. 22:120-124. Hoagland, D.R. and 0.1. Arnon. 1950. The water culture method for growing plants without soil. Calif. Agric. Expt. St. Circ. 347. 32 pp. Jacques. G.L. and R.G. Harvey. 1979. Dinitroaniline herbicide phytotoxicity as influenced by soil moisture and herbicide vaporization. Weed Sci. 27:536-539. Jacques, G.L. and R.G. Harvey. 1979. Vapor absorption and translocation of dintroaniline herbicides in oats (Avena sativa) and peas (Pisum sativum). Weed Sci. 27:371-374. Jordan, T.N., R.S. Baker and W.L. Barrentine. 1978. Comparative toxicity of several dintroaniline herbicides. Weed Sci. 26:72-75. Negi, N.S. and H.H. Funderbunk, Jr. 1968. Effect of solutions and vapors of trifluralin on growth of roots and shoots. Abstr. Weed Sci. Soc. Amer. pp.37. Parker, C. 1966. The importance of shoot entry in the action of herbicides applied to the soil. Weeds 14:117-121. Putnam, A.R. and M.D. Willis, et al. 1979. Horticultural report, Michigan State University. 31:18-25. Putnam, A.R. and M.D. Willis, et al. 1980. Horticultural report, Michigan State University. 32:25-27. Savage, K.E. 1978. Persistence of several dinitroaniline herb- icides as affected by soil moisture. Weed Sci. 26:465-471. Schultz, D.P., H.H. Funderburk, Jr. and N.S. Negi. 1968. Effect of trifluralin on growth, morphology. and nucleic acid synthesis. Plant Physiol. 43:265-273. 104 15. 16. 17. 18. 105 Strang, R12. and R.L. Rogers. 1971. A microradioautographic study of C-trifluralin absorption. Weed Sci. 19:363-369. Swann, C.W. and R. Behrens. 1972. Phytotoxicity of trifluralin vapors from soil. Weed Sci. 20:143-146. Upadhyaya, M.K. and L.D. Nooden. 1977. Mode of dinitroaniline herbicide action 1. Analysis of the colchicine-like effects of dinitroaniline herbicides. Plant & Cell Physiol. 18:1319-1330. Willis, M.D. and A.R. Putnam. 1981. Use of ethalfluralin for weed control in cucurbits. Abstr. HortScience 16:457. APPENDIX 107 Appendix Table A1. Soil Analysis of Spinks Loamy Sand. Soil PH: 5.7 % 0.M. 2.84 CEC: 12.69 MEQ/Gram Nutrients Assay phosphorus 233 kg/ha potassium 367 kg/ha calcium 1912 kg/ha magnesium 251 kg/ha nitrate 146.2 PPM iron 44 PPM manganese 3 PPM zinc 3 PPM Exchangeable Percent bases of total potassium 7.5 calcuim 75.9 magnesium 16.6 108 Table A2. Extraction and phase separation of radioactivity in cucumbers after 2, 6, 24 or 48 h root exposure to 14C-etha1fluralin. Recovered Radioactivity Exposure Plant CHZCI2 Water CH3OH Time Part Phase Phase Insoluble (% of Total) 2 h Root 50.9 44.7 4.4 Stem 77.1 16.3 6.6 Cotyledon 81.9 11.7 6.4 Total 52.4 43.1 4.5 6 h Root 48.6 37.1 14.3 Stem 75.6 13.4 11.0 Cotyledon 65.6 24.4 10.0 Total 53.3 33.2 13.5 24 h Root 22.7 30.1 47.2 Stem 43.6 36.1 20.2 Cotyledon 44.9 31.8 23.3 Total 31.1 31.3 37.6 48 h Root 15.8 29.8 54.4 Stem 28.2 45.0 26.8 Cotyledon 30.0 39.5 30.5 Total 21.9 34.7 43.4 109 Table A3. Extraction and phase separation of radioactivity in beans after 2, 6, 24 or 48 h root exposure to 14C-ethalfluralin. Recovered Radioactivity Exposure Plant” ChZCl2 Water Ch30H Time Part Phase Phase Insoluble -———————(% of Total) 2 h Root 76.6 12.9 10.5 Stem 92.6 4.8 2.6 Cotyledon 63.7 20.3 16.0 Total 82.0 10.3 7.7 6 h Root 50.6 25.2 24.2 Stem 71.9 13.5 14.6 Cotyledon 56.6 25.8 17.6 Total 53.6 23.8 22.6 24 h Root 21.9 27.8 50.3 Stem 39.4 27.6 33.0 Cotyledon 39.2 33.7 27.1 Total 25.1 28.2 46.7 48 h Root 14.7 28.1 57.2 Stem 44.9 19.2 35.9 Cotyledon 30.6 34.8 34.6 Total 21.5 27.5 51.0 BIBLIOGRAPHY BIBLIOGRAPHY Adeniji, A.A. and D.P. Coyne. 1981. Inheritance of resistance to trifluralin toxicity in Cucurbita moschata Poir. HortScience 16:774-775. Alder, E.F., W.L. Wright and Q.F. Spoer. 1960. Control of seedling grasses in turf with diphenylacetonitrile and a substituted dinitroaniline. Proc. North Cent. Weed Control Conf. 17:23-24. Anderson, W.P. 1977. Weed Science: Principles. West Publishing Co., New York. 598 pp. Anderson, W.P., A.B. Richards and J.W. Whitworth. 1968. 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