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LIBRARY BINDERS SPRINOMRT llama“ ABSTRACT BENTAZON SELECTIVITY AND METABOLISM BY Martin Donald Mahoney The responses of soybean (Glycine max (L.) Merr.), navy bean (Phaseolus vulgaris L.), cocklebur (Xanthium pgnnsylvanicum Wallr.) and black nightshade (Solanum nigrum L.) to postemergence applications of bentazon (3-isopropyl-lg-2,1,3 benzothiadiazin-(4)3§fone 2,2- dioxide) at the rate of 1.12 kg/ha, were evaluated in greenhouse studies. The basis for selectivity of bentazon allowing navy bean tolerance, cocklebur susceptibility and black night- shade moderate susceptibility was evaluated by studying spray retention, translocation and metabolism. Transloca- tion and metabolism were also examined in tolerant soybean. The trifoliate leaves of navy bean retained less bentazon than the unifoliate leaves of navy bean and the leaves of seedling cocklebur and black nightshade. The 14C-labelled compounds from l4C-bentazon applied to the foliage of black nightshade was translocated throughout the entire plant. In navy bean, the l4C-labelled compounds Martin Donald Mahoney were localized in the treated area of the first trifoliate leaflet with acrOpetal movement. However, acropetal and basipetal movement were observed throughout the unifoliate navy bean and trifoliate soybean seedlings. In cockelbur, the 14 C -labelled compounds diffused throughout the entire treated leaf only. There were differences among species in the rate of metabolism and the l4C-metabolites formed from 14C-bentazon l and 5 days after treatment. Metabolism of bentazon was most rapid in the trifoliate leaves of navy bean. Translocation and metabolism studies were also conduc- ted in navy bean seedlings with their first fully expanded - trifoliate leaf, following prior treatments with EPTC (gfethyl dipropylthiocarbamate), chloramben (3-amino-2,5- dichlorobenzoic acid) and trifluralin (a,aflrtrif1uoro-2,6- dinitro-§,§-dipropyl-p-toluidine). AcrOpetal and basipetal l4C-labelled compounds occurred in EPTC translocation of pretreated navy beans. Although prior herbicide treatments did not decrease the rate of metabolism of the kinds of metabolites found, the percentage of metabolites varied among treatments. In soybean, four apparent 14C-conjugates were found in plants allowed to grow until full maturity. BENTAZON SELECTIVITY AND METABOLISM BY Martin Donald Mahoney A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of CrOp and Soil Sciences 1974 ff’ ACKNOWLEDGEMENTS The author wishes to gratefully acknowledge the assis- tance of Dr. Donald Penner in conducting this study and in making the Opportunity at Michigan State University possible. The author also wishes to thank Drs. W.F. Meggitt, M.J. Zabik, and J.W. Hanover for their assistance. Also, the technical assistance of Thomas and Renee Lareau is gratefully acknowled- ged. ii TABLE OF CONTENTS page LIST OF TABLES ..... ........... . ............ .... ..... .. V LIST OF FIGURES ... .......... ................ ..... ..... Vii INTRODUCTION ........... ...... . ....... ... ......... ..... 1 Chapter 1: LITERATURE REVIEW 0.00.00.00.0000.00.00.... 2 Weed Problems in Navy Bean and Soybean ........... 2. Postemergence Herbicides for Weed Control in Soybean and Navy Bean ................ ..... .... 3 Chapter 2: BENTAZON TRANSLOCATION AND METABOLISM IN SOYBEAN AND NAVY BEAN ..... .................. ......... 10 Abstract ..... ..... ........... ...... ............. 10 Introduction ... ......... ........................ 10 Materials and Methods . ...... .................... 12 Results and Discussion ................. ..... .... 14 Literature Cited ................................ 35 Chapter 3: THE BASIS FOR BENTAZON SELECTIVITY IN NAVY BEAN, COCKLEBUR AND BLACK NIGHTSHADE ... ...... .. 36 Abstract ........................................ 36 Introduction ........ ...... ... ..... .............. 37 Materials and Methods .... ...... ................. 37 Results and Discussion ... .......... ............. 39 Literature Cited ................ ..... ........... 52 iii page Chapter 4: SUMMARY AND CONCLUSION ................... 53 LISTOF REFERENCES ......0....... ...... ......0...00... 55 iv LIST OF TABLES Table Chapter 2 l. R values of 14C-bentazon metabolites from t e center leaflet of the first trifoliate navy bean leaf. ..... ................ ...... ....... Metabolism of l4C-bentazon in the unifoliate leaf apex of navy bean, l and 5 days after treatment. ...................... ... .............. Comparison of unmetabolized 14C-bentazon between the navy bean unifoliate leaf apex with time and the center navy bean trifoliate leaflet. ..... . ......................... . ......... Metabolism of l4C-bentazon in the center navy bean trifoliate leaflet apex 1 day after l4C-bentazon application following various herbicide treatments. .................... The effect of previous herbicide treatments on the change in percent of unmetabolized 14C-bentazon in the center navy bean trifoliate leaflet, 1 and 5 days after l4C- bentazon application. ... ...... . .................. Rf values of the l4C-bentazon metabolites from the center leaflet of the first trifoliate soybean leaf. ......... . ........ . ...... Metabolism of l4C-bentazon in the center leaflet of the first trifoliate soybean leaf, 1 and 5 days after treatment. ..... ......... Chapter 3 10 Leaf retention of bentazon after foliar application. 00.00.000.00. 000000000 0 00000000000000 page 31 32 33 34 Table page 2. Metabolites of 14C-bentazon and corres- ponding Rf values obtained from leaf and leaflet apices of various plant species harvested 1 and 5 days after treatment. .. ....... 48 Metabolism of 14C-bentazon in the leaf apices of unifoliate and trifoliate leaves of navy bean, leaves of cocklebur and black nightshade 1 day after treat- ment. ... ......... ...... ........ ... .............. 49 Comparison of l4C-bentazon uptake and remaining unmetabolized bentazon between leaf apices of various plant Species harvested 1 and 5 days after treatment. ......... 50 Comparison of total l4C-bentazon accumu- lation and remaining unmetabolized bentazon from leaf apices of various plant species 1 and 5 days after treatment. ..... 51 vi LIST OF FIGURES Figure page Chapter 2 l. Translocation of l4C-bentazon in navy bean. The treated plants (A) and the corresponding radioautograph (B) show navy bean with only unifoliate leaves harvested 1 day after foliar application. The treated plants (C) and corresponding radioautograph (D) show navy bean at the same stage of growth har- vested 5 days after foliar application. .......... l8 Translocation of 14C-bentazon in navy bean. The treated plants (A) and corresponding radioautograph (B) show navy bean having trifoliate leaves, harvested 1 day after foliar application. The treated plants (C) and corresponding radioautograph (D) show navy bean at the same stage of growth har- vested 5 days after foliar application. .......... 20 Translocation of 14C-bentazon in navy bean with a prior herbicide treatment of EPTC. The treated plants (A) and corresponding radioautograph (B) show navy bean having trifoliate leaves harvested 1 day after foliar application. The treated plants (C) and corresponding radioautograph (D) show navy bean at the same growth stage harvested 5 days after foliar application. ................. 22 Translocation of 14C-bentazon in soybean. Treated plants (A) and corresponding radio- autograph (B) show soybean having trifoliate leaves harvested 1 day after foliar appli- cation. Treated plants (C) and correspon- ding radioautograph (D) show soybean at the same stage of growth harvested 5 days after foliar application. .............................. 24 vii Figure page S. graph showing the characteristics of the 4C-metabolites obtained from the methanol-soluble extract of l4C-bentazon treated soybeans allowed to grow until maturity as determined by molecular sieve chromatography. Peaks, B, C and D show the fractions where the most 14C-metabolites were eluted from the columns whose Rf values correspond to those of B, C and D of Table 1. ......... ...... ...... ..... .......... 26 Chapter 3 1. Translocation of 14C-bentazon in black nightshade. The treated plants (A) and corresponding radioautograph (B) show black nightshade with four to six leaves, har- vested 1 day after foliar application. The treated plants (C) and corresponding radio- autograph (D) show black nightshade at the same stage of growth harvested 5 days after foliar application. ............. . ..... . ........ 44 Translocation of l4C-bentazon in cocklebur. The treated plants (A) and the correspon- ding radioautograph (B) show cocklebur , with four to six leaves harvested 1 day after foliar application. The treated plants (C) and corresponding radioauto- graph (D) show cocklebur at the same stage of growth harvested 5 days after foliar application. ........................ . .......... 46 viii I NTRODUC TI ON Bentazon (3-isopr0pyl-lH-2,l,3 benzothiadiazin-(4)3§- one 2,2-dioxide) has shown considerable promise as a post- emergence herbicide for selective control of many broad- leaved weeds in soybeans (Glycine max (L.) Merr.) (4, l9). Weeds selectively controlled include cocklebur (Xanthium pennsylvanicum Wallr.), wild mustard (Brassica kaber D.C.), common ragweed (Abutilon the0phrasti Medic.). In Michigan, navy bean (Phaseolus vulgaris L.) acreage approximates the soybean acreage with similar weed problems. Several preplant incorporated and preemergence herbicides, currently being used for the two crOps, are the same. How- ever, in many instances, they are not effective in both navy bean and soybean. Bentazon has also shown promise as a postemergence herbicide for the control of broadleaved weeds in navy beans (20). However, effective total weed control in both navy bean and soybean requires bentazon combinations with preplant incorporated or preemergence herbicides. The purpose of this research was to determine the basis for the selectivity of bentazon between navy bean and some weed Species, to determine the effect of prior herbicide treatments on navy bean tolerance to bentazon, and to compare metabolism of bentazon in navy bean with soybean. l Chapter 1 LITERATURE REVIEW Weed Problems in Navy Bean and Soybean In the United States, weeds in soybean (Glycine max (L.) Merr.) have been found to reduce the potential value of the crOp almost 17 percent per year (12). McWhorter and Hartwig (9) found that common cocklebur (Xanthium pennsylvanicum Wallr.) alone can reduce the average yields in certain soy- bean varieties by as much as 75%. Hicks et al. (9) have shown that light penetration with- in the soybean canOpy influenced soybean yields. Reduced penetration of light into the canopy due to a heavy weed infestation, reduced soybean yields. Weeds can also increase lodging of soybean plants. Weber and Fehr (18) reported yield losses of 32 kg/ha due to this cause. Navy bean (Phaseolus vulgaris L.) fields, with a heavy infestation of cocklebur usually Show reduced vigor, growth and yield, which is generally attributable to the more rapid and larger growth of cocklebur. Weeds may also reduce the quality of navy bean seed because of the nature of the harvesting method. In Michigan, harvesting navy beans to- gether with the purple black nightshade (Solanum nigrum L.) 2 berries causes discoloration to the navy bean seed. This reduction in quality has caused considerable economic losses to Michigan navy bean growers. Postemergence Herbicides for Weed Control in Soybean and Nagy Bean Preemergence herbicides frequently give less than the desired level of weed control in both soybean and navy bean. This has generated considerable interest in compounds that may be applied in a postemergence manner. Herbicides applied in this manner to soybean include chloroxuron (3- [p-(p-chlorophenoxy) phenyl]-l,l-dimethyl urea), 2,4-DB (2,‘ 4-dichlor0phenoxy butyric acid), and bromoxynil (3,5-dibro- mo-4-hydroxybenzonitrile). Bentazon (3-iSOpropyl-lflf2,l,3 benzothiadiazin-(4)BH-one 2,2-dioxide) currently has an experimental label for this use. Postemergence applications of chloroxuron to soybean, at rates of 0.84, 1.12, 1.68, and 3.36 kg/ha, injured and initially stunted all plants (2, 5, 11). The leaves ex- hibited a burned appearance with some subsequent defolia- tion. Delayed maturity, reduced stands and yields were also reported (2, 5, 11). When these effects were observed, the soybean had only their unifoliate leaves. Applications to soybeans having their first, second and third trifoliate leaves seldom delayed maturity or reduced yields. Parachetti et a1. (1) found that postemergence applications of chloroxuron to soybeans did not significantly reduce yields if applied after a preemergence soybean herbicide, provided the soybeans had at least one fully eXpanded tri- foliate leaf. Baldwin and Frans (5) controlled cocklebur with chloroxuron only if the plant was in its cotyledonary stage of growth, and a high (3.36 kg/ha) rate was applied. Gossett et a1. (8) obtained excellent control of cocklebur with chloroxuron at rates of 0.56 and 1.12 kg/ha if a surfactant (dodecyl ether polyethylene glycol) was used and the cockle- bur seedlings were under 8 cm in height. The selective action of chloroxuron on soybean (toler- ant species) and tall morning glory (Ipomea purpurea (L.) Roth) (susceptible species) was examined by Feeny et a1. (6). Selectivity of postemergence applications was based on dif- ferential foliar absorption and greater retention of chlor- oxuron by the susceptible species. Tall morning glory con- tained eight times more radioactivity than soybean one-week- old seedlings. ChlorOplasts from tall morning glory initially retained two times more chloroxuron than did chloroplasts from soybean after foliar treatment. Differen- tial metabolism was not considered as a basis of selectivity between these two species. When chloroxuron was root-applied, soybean accumulated more chloroxuron in the root than did tall morning glory. However, the soybean roots appeared to be effective barriers to acropetal transport as tall morning glory allowed chlor- oxuron to acculuate in the foliage causing phytotoxicity. Chloroxuron is a photosynthetic inhibitor, so accumulation in the photosynthetic tissue is critical. Postemergence applications of 2,4-DB at the rate of 0.44 kg/ha resulted in more injury to soybean than chlor- oxuron applied at 3.36 kg/ha (8, l6). 2,4-DB also reduced soybean yields more than chloroxuron. However, excellent control of cocklebur has been obtained with 2,4-DB with rates as low as 0.44 kg/ha (8). Wathana et a1. (15) compared the uptake and transloca- tion of 2,4-DB in soybean and cocklebur. The penetration rate of 2,4-DB was faster in cocklebur than in soybean after one day. In soybean, only trace quantities of 2,4-DB were translocated from the treated leaf to the other plant parts. In cockelbur, there was considerably greater movement of the herbicide into the meristematic tissues of the plant. Bromoxynil has also been shown to cause early injury and delayed maturity to soybeans when applied at rates of 0.07, 0.14, 0.196 and 0.252 kg/ha (3). However, excellent cockle- bur control was obtained if the high rates of bromoxynil were used. Wax et al. (17) also found some yield reduction from bromoxynil treated soybeans at rates of 0.3 and 0.4 kg/ha. Van Amsberg et a1.1 first reported the use of bentazon as a selective postemergence herbicide for the control of 1Von Amsberg, H., J.P. Pearson, J.W. Daniel, A.L. Weishar, C.W. Carter, M.A. Veenstra, J.T. Thompson, and B. Wuerzer. 1971. Effects of 3-isopr0pyl-1H-2,l,3-benzothiadiazin-(4) 3H-one 2,2 dioxide (Bas—3512-H) on Soybeans and Broadleaved Weeds at Various Stages of Growth. Weed Sci. Soc. Amer. Abstr. No. 106. broadleaved weeds in soybeans. They reported that soybeans with unifoliate, and first through fourth trifoliate leaves were tolerant to applications of bentazon at rates ranging from 0.84 to 2.24 kg/ha. Common cocklebur was susceptible' to bentazon at all rates used. Cocklebur was found to be susceptible up to and occasionally including the flowering stage. Weber et a1. (19) found minimal injury to soybean, and excellent control of cocklebur with bentazon at the rate of 1.12 kg/ha. Wax et al. (17) found soybean to be tolerant to bentazon applications of 3.36 kg/ha at the unifoliate and first and second trifoliate stages of growth. Soybean was also found to be more tolerant to applications of bentazon than bromoxynil, chloroxuron and 2,4-DB. When applications of these herbicides were made on soybean cultivars introduced from Japan, extensive injury resulted. The herbicide causing the least amount of injury to these cultivars was chloroxuron (17). Anderson et a1. (13) found reductions in yield from bentazon applications under high soil moisture conditions. Soybeans grown in soil with moisture levels not exceeding field capacity showed no injury to postemergence applications of bentazon. Penner (12) related selectivity of bentazon between tolerant soybean and susceptible Canada thistle (Circium arvense L.) to differences in leaf retention and the rate of bentazon metabolism. Less bentazon was retained on the leaves of soybean than in Canada thistle. After one day, 25 to 35 percent bentazon remained unmetabolized in Canada thistle, whereas only 16 percent of the bentazon remained unmetabolized in soybean. Bentazon has been shown to exhibit a strong movement toward the anode in an electrical field in water or'a neutral solution (1). It leached quite readily from the soils and was not adsorbed to any of the soils tested thus far. Bentazon adsorbed readily to an anion exchange resin, but did not adsorb to a cation exchange resin at a pH of 7. When the pH of both resins was adjusted to 2 or 12, a small amount of bentazon did adsorb to the cation exchange resin, while less was adsorbed to the anion exchange resin than that found at a neutral pH. These results indicate that bentazon exhibits strong anionic properties when placed in neutral solutions or soils with a pH range of 5 to 7. In nonflooded soils, the absorption of bentazon from the soil does not seem to be a factor affecting its action. Currently, there are no postemergence herbicides for navy bean, kidney bean, pinto bean, etc. (Phaseolus vulgaris L.), that control weeds without Causing extensive injury and yield reduction to these beans.2 Bentazon, which shows promise as a postemergence herbicide for soybeans, also appears promising as a postemergence herbicide for the con- trol of certain broadleaf weeds in other beans. Preplant incorporated or preemergence herbicides must be used in 2Personal Communication. Donald Penner, Michigan Statei'. University, East Lansing, Michigan. combination with bentazon if effective, overall weed control is to be achieved.3 Fenster and Wicks (7) have shown good to excellent weed control in Great Northern "No. 59" field beans with bentazon at the rate of 0.84 kg/ha in combination with preemergence applications of alachlor (2-chloro-2',6'—diethyl -N—(methoxymethyl) acetanilide) at the rate of 2.24 kg/ha and preplant incorporated EPTC (S—ethyl dipropylthiocarba— mate) at the rate of 1.68 kg/ha. In some cases slight injury did occur, but there was no significant yield reduction if compared to the hand weeded check. In Michigan, navy beans are a major crOp. The use of bentazon in combination with preplant incorporated or pree emergence herbicides for weed control is also of interest. Bentazon applied alone at the rate of 1.68 kg/ha controlled 88 percent of the black nightshade. In some cases, complete kill was not obtained and regrowth of black nightshade did occur (20). Bentazon applications at the rate of 1.12 kg/ha in combination with preplant incorporated treatments, gave excellent control of all broadleaved weeds present. Bentazon applications at rates of 0.84, 1.12, and 1.68 kg/ha to navy beans before the first trifoliate leaf was fully expanded, resulted in severe injury accompanied by stand reduction.4 However, bentazon applications at the same rates to navy beans with the first and second trifoliate leaves fully expanded caused only slight injury, and the 3Personal Communication. Donald Wyse, Michigan State University, East Lansing, Michigan. 41bid. yields did not differ significantly from the hand weeded check.5 Ibid. Chapter 2 BENTAZON TRANSLOCATION AND METABOLISM IN SOYBEAN AND NAVY BEAN Abstract Bentazon (3-isopr0pyl—1H 2,1,3 benzothiadiazin—(4)3H— one 2,2-dioxide) shows promise as a selective postemergence herbicide for the control of weeds in soybean (Glycine max (L.) Merr.) and navy bean (Phaseolus vulgaris L.). Following foliar l4C-bentazon application, the movement of 14C was primarily acrOpetal in both species. However, basipetal movement was also observed. Metabolism was more rapid in the trifoliate navy bean leaf than in the unifoliate navy bean leaf and the trifoli- ate soybean leaf. Prior herbicide treatments did not de- crease metabolism of bentazon in navy beans. The metabolites in navy bean and soybean appeared similar. Four apparent l4 C-conjugates were isolated from soybean plants harvested at full maturity. Introduction Current preplant and preemergence applications of her- bicides available for weed control in soybean and navy bean 10 11 do not control the full range of problem weeds. Broadleaf weed infestations, such as cocklebur (Xanthium pennsylvani- cum Wallr.), have increased due to the decrease in compe- tition from other weeds controlled by preplant and pre- emergence applications of herbicides (4, 6). Postemergence applications of 2,4-DB (2,4,-dichloro- phenoxy butyric acid), chloroxuron (3-[p3(p-chlorophenoxy) phenyl]-l,l-dimethyl urea) and bromoxynil (3,5-dibromo—r- hydroxybenzonitrile) to soybean control many broadleaf weeds, such as cocklebur, but may also cause extensive injury to soybean (1, 2, 4, 6, 7, 9, 10). Bentazon, used as a postemergence herbicide for weed control in soybean,‘ has shown excellent control of cocklebur and other problem weeds with minimum injury to soybean (3, ll). Bentazon also shows promise as a postemergence herbicide for weed control in navy beanl (5). However, bentazon injury to navy bean plants having only unifoliate leaves has been observed in the field. Our objectives were to determine the movement of 14C from 14C-bentazon in soybean and navy bean, to examine dif- ferences in translocation of 14C between unifoliate and first trifoliate leaves of navy bean, to determine the influence of herbicide pretreatments on bentazon translocation and metabolism, and to compare bentazon metabolism in soybean and navy bean. 1Wyse, D.L., W.F. Meggitt and R.C. Bond. 1973. New herbi- cides for navy beans. Research Report, N. Cent. Weed Contr. Conf. 28:76-79. 12 Materials and Methods "Hark" soybean and "Sanilac" navy bean were grown in Conover sandy loam soil in the greenhouse with supplemen- tal fluorescent lighting. For the study on the influence of herbicide pretreatments, EPTC (g—ethyl diporpylthiocar- bamate) at 3.36 kg/ha, trifluralin (a,a,a—trifluoro-2,6- dinitro-N,N—dipropyl-P—toluidene) 0.56 kg/ha were applied preplant incorporated and chloramben (3-amino-2,5-dichloro- benzoic acid) at 2.24 kg/ha was applied in a preemergence manner. To study the translocation of 14C-bentazon in navy bean and soybean seedlings, a 5ul dr0plet containing 0.2uCi of 14C-bentazon was placed at the base of the unifoliate leaf or at the base of the center leaflet of the first trifoliate leaf. The bentazon had a specific activity of 2.97 mCi/mo mole and was labelled in the number 10 position. Plants were harvested 1 and 5 days following treatment, freeze dried, mounted and radioautographed. For the metabolism study, plants were treated with 14C-bentazon in the same manner as in the translocation 14C-benta- experiment. The leaf apecies above the site of zon application were harvested, homogenized in absolute methanol, and the homogenate filtered through Whatman num- ber 1 filter paper under vacuum. The methanol-insoluble portion was combusted under 02 by the method of Wang and Willis (8), and the radioactivity determined by liquid scintillation spectrometry. The methanol-soluble portion 13 was evaporated to dryness in 23329, resuspended in 15 ml methanol:water (1:2; v/v) and partitioned against 15 m1 benzene and ethyl acetate three times in 5 ml fractions. All of the samples were then evaporated to dryness in 33939 and resuspended in 1 m1 of their respective solvents. One-hun- dred ul of each fraction was then radioassayed and 400 pl were Spotted on 250 micron thick silica gel F-254 thin layer chromatography plates. The plates were develOped in a sol— vent system of chloroformzmethanol (7:3; v/v). After devel- opment to a height of 15 cm, the plates were radioautographed. The l4C-labelled spots on the plate were removed and radio- assayed by liquid scintillation spectrometry. Methanol-soluble extracts from soybean, allowed to grow until they reached full maturity, were obtained from the BASF Wyandotte Corporation. The nature of the 14C-metabolites was determined by gel filtration or molecular sieve chromatog- raphy, with subsequent spotting on thin layer plates as in the metabolism study. The methanol-soluble extracts were concentrated from 10 ml to 1 ml. Five-tenths ml were then placed on a sephadex G—15 gel column 15 cm high and 1 cm in diameter. The columns were eluted with water at a flow rate of 0.075 ml/min. One ml fractions were collected and 200 pl from each fraction radioassayed by liquid scintillation spectrometry. The fractions showing the greatest quantities of radioactivity were then spotted on thin layer plates and developed as previously stated. 14 All data presented in the tables are the means of two experiments with three replications per experiment. Figures are representative of two or more experiments. Results and Discussion Foliar applications of 14C-bentazon to the unifoliate leaves of navy bean seedlings resulted in acrOpetal and basi- petal trnaslocation of the 14 C from the site of application (Figure 1). After 5 days the extent of movement was similar to that found after 1 day. Foliar applications made to the center leaflet of the first trifoliate leaf of navy bean re- 14C from. sulted in acrOpetal but no basipetal movement of the site of application after 1 or 5 days (Figure 2). This could be a possible explanation of why navy bean plants having trifoliate leaves are more tolerant to foliar appli- cations of bentazon than plants having only unifoliate leaves. Navy bean grown in EPTC-treated soil showed more acro- 14C in the treated trifoliate leaflet l petal movement of day after treatment than was observed in plants not receiving the herbicide pretreatment (Figures 2 and 3). However, the EPTC treatment did not alter navy bean tolerance to foliar applications of bentazon. The chloramben and trifluralin treatments did not affect 14C movement in navy bean. In soybean, movement of 14C from foliar applications of 14C-bentazon was primarily acrOpetal accompanied by some basipetal movement (Figure 4). After 5 days, both acrOpetal 15 and basipetal movement was more extensive (Figure 4). The same number of metabolites were found in the uni- foliate leaf apex as in the center trifoliate leaflet apex of navy bean (Tables 1 and 2). They were probably the same, since the Rf values were very similar from the leaf apices of the two species. However, the percent of 14C remaining as unmetabolized bentazon was significantly higher in the unifoliate navy bean leaf apex than in the center trifoliate leaflet apex after one day (Table 3). This offers another eXplanation of the observed differences in tolerance of navy bean at the two stages of growth to foliar applications of bentazon. Prior herbicide treatments did not significantly de- crease the rate of 14C-bentazon metabolism after 1 day in navy bean compared to the control (Table 4). Navy bean growth on EPTC-treated soil showed a significantly increased rate of bentazon metabolism in the center trifoliate leaflet apex compared to the control. This higher rate of bentazon metabolism may counterbalance the increased translocation caused by the EPTC treatments or be an explanation for it. After 5 days, the percent of metabolized bentazon did not differ significantly from that found after 1 day in the center trifoliate leaflet apices of navy bean with and without prior herbicide treatments (Table 5). Metabolism of 14C-bentazon on soybean and navy bean appeared to be similar in the number of metabolites found and their characteristics. However, most of the Rf values 16 of the 14C-metabolites from soybean were slightly different than those from navy bean (Tables 1 and 6). The percent of unmetabolized bentazon 1 day after 14C-bentazon application was much higher in the center trifoliate leaflet apex of soybean than navy bean (Table 7). Five days after treatment there was a significant reduction in the percent of unmetab- olized bentazon in soybean. Because of the slow initial rate of bentazon metabolism in soybean, and the movement of 14C throughout the plant, other factors may also play a role in the observed tolerance of soybean to bentazon. Methanol-soluble extracts obtained from 14C-bentazon treated soybeans harvested at maturity revealed three peaks of radioactivity when subjected to molecular sieve chroma- tography (Figure 5). The metabolites appeared to be 14C- bentazon conjugates as eluted from the column between stan- dards with known molecular weights of approximately 698 and 269 (Figure 5). The predominate 14C-metabolite was resolved into two bands of radioactivity by TLC indicative of two metabolites present in this peak. Thus, four apparent 14C- 14C-benta- bentazon conjugated metabolites were isolated from zon-treated soybean harvested at maturity. Metabolism and translocation of bentazon appear to be major factors in the greater tolerance of navy bean, having trifoliate leaves when bentazon was applied, compared to those having only unifoliate leaves. Prior herbicide treatments did not Significantly decrease metabolism of bentazon in trifoliate leaflet apecies of navy bean. l7 Trifoliate leaves of soybean translocated more 14C and metabolized a smaller percentage of bentazon than trifoli- ate leaves of navy bean, indicating the possible role of other factors contributing to the tolerance of soybean to foliar applications of bentazon. 18 Figure 1. Translocation of l4C-bentazon in navy bean. The treated plants (A) and the corresponding radio- autograph (B) show navy bean with only unifoliate leaves harvested 1 day after foliar application. The treated plants (C) and corresponding radio- autograph (D) Show navy bean at the same stage of growth harvested 5 days after foliar application. l9 Figure 2. 20 Translocation of 14C-bentazon in navy bean. The treated plants (A) and corresponding radioauto- graph (B) show navy bean having trifoliate leaves, harvested 1 day after foliar application. The treated plants (C) and corresponding radioauto- graph (D) show navy bean at the same stage of growth harvested 5 days after foliar application. Figure 3. 22 Translocation of l4C—bentazon in navy bean with a prior herbicide treatment of EPTC. The treated plants (A) and corresponding radioautograph (B) show navy bean having trifoliate leaves harvested 1 day after foliar application. The treated plants (C) and corresponding radioautograph (D) Show navy bean at the same growth stage harvested 5 days after foliar application. ~74__— L.._ .11 23 24 z“ 5 ._ .x. a. :— ‘.. .. ... 1 1 n .C .3 ... u .p. a. .t .. =. 2. .2 .. a. E _. S o .L . . . 2 ... u‘ ..u I .. . .s‘ S .r a. o. T ... I . 3 I: I: T . . w. a” “a. 1: 3 I . .. ‘3 .u .? .. s\ \x . . . . . . s. a. .a .. . s.‘ \.“ 4‘ \\ \\ v. ‘. 4. I . . ... “s. t“ 1‘ “..r. a“ E .- ~V u. r I... t“ 3“ .. .i 1 i 4 g a. n“ \\ ‘K :“ ... “T ‘1 .x. Ks ... \i ... ‘1 ... xx .. ma \\\ ... \s :u \s \ .;.: s ‘.“ I E t. ~ ~. :. 3‘ ‘4 .. .. t. ‘4 \. “s. .\\ a :\ t“ 25 26 3 Hsn-yn'w so“...‘ 1.. \g .2 s. ... 9 E 3.. 2 E 5 ... : ... S c s . : 3 .... .3 9 V. “IL“ I 3 t l v. r . _ S u. \e r o. .- x: 3 2“ .u. .. .... I C \¢ v. 5 l ..u a" t C C a“ 4‘ n.» as t V C m- e a C .1 r I S .9. 3‘. r 9 C 3.3 tvit S 5 q . v . .3 o w. s . ... 5 .3 u . g . a. ... 5 ... .2 U C a. t 5 p“ ... 27 .02 20.55... 2 3 a. o_oakom¢m~._ w a >._._m2m.—Z_ .d «0‘00 oom— Ema mn¢ ZON._..m2m._.2_ «0.00 “.0 ho...— 28 Table l. Rf values of 14C-bentazon metabolites from the center leaflet of the first trifoliate navy bean leaf. Metabolites Rf Ethyl acetate-soluble .18 Water-methanol-soluble A .00 Water-methanol-soluble B .12 Water-methanol-soluble C .19 Water-methanol-soluble D .26 l4C-Bentazon .68 29 .pcsom mufl>wuomofipmn Hmuou mo unmouom mo meumu aw pmmmmumxm mum m¢5am>n .wflmmamcm HMOfiumHumum How mcflmonm on» CD meHommcmHu mum3 mmsHm> pamoumm .Hm>ma mm may um ucwuwmwflp Maucmofiwflcmaw uoc mum mumuuma mean can nua3 mGEdHoo canvas mamsz m m.m n o.mm m ~.m m m.HN m H.m n m.sa n 0.0 m n m.m~ m S.H~ m m.m m m.ma a o.HH m H.HH m o.o H .m. .m. .mv .w. .w. .w. .w. .mmmo. :onucmn mHQDHOmcw Q U m d mansaom cowumuso IUqa Iaocmnumz wH23HOmIHosmnumz Imumumom Hanan ucmfiummua hm.ucmeummnu umumm mmmo m paw H .cmmn hbmc mo xwmm mama mDMAHOMHG: may CH :onucmn|UvH mo Emwaonmumz .N wanna 30 Table 3. Comparison of unmetabolized 14C—bentazon between the navy bean unifoliate leaf apex with time and the center navy bean trifoliate leaflet.a Treatment Treatment Unmetabolized site duration l4C-bentazon (days) (%) Trifoliate 1 12.0 a Unifoliate 1 28.8 b Unifoliate 5 8.6 a aMeans with the same letters are not significantly different at the 5% level. Percent values were transformed to the arcsine for statistical analysis. 31 .pcsom mua>flpomowpmu Havoc mo unwoumm mo meuwu cw pmmmmumxm mum mwsHm> @GHmUHw Gnu. Cu. UGEOmmGMHu. 0H03 WQDHM> “COUHOQ Q .mwmmamcm Hmowpmflumum How .umou mmcmn onHuHDE m.cmocso ma Hm>ma mm may um unmnommwp SaucmoHMHcmfim uoc mum mumpuma mean on» suHB mcEdHoo casufl3 mammZM n e.oH h o.em m H.m n s.o~ m m.OH m m.ma m m.o m.o :AHmHSHMAue o m.ma m G.H~ n 0.4H m m.a~ a H.4H m o.ma h N.H o.~ :mhemuoHsu m n.m n H.em m o.m m 4.HN o v.o~ m o.ma h 4.H o.m 09mm on o.~H hm m.~m m m.m m o.H~ o m.o~ m o.mH m 5.0 - Houuaoo .w. .w. .4. .wc .mv .wv .w. .4\ha. conucmn mHQ5H0mcw Q U m m mannaom mumm mucmEummHu nu uaosmnumz wannaomuaocmnumfilumumz nmumuoom mofloflnuwm «a Hmnum Am.mucmfivmmuu mofiownuwn msofium> mcflsoHHOM coflpmowammm co~mucmnuova Hmumm mac H xmmm umawmma muMHHOMHHu sown m>mc umucoo mnu cw conucmnnu mo Emflflohmumz . m m vH v an E 32 Table 5. The effect of previous herbicide treatments on the change in percent of unmetabolized 14C-bentazon in center navy bean trifoliate leaflet, l and 5 days after 14C-bentazon application.a Treatment Herbicide treatment #1 duration Control EPTC Chloramben Trifluralin (déys) (M (‘3) (M (is) 1 12.0 a 5.7 a 12.5 a 10.7 a 5 9.4 a 4.1 a 8.0 a 8.0 a aMeans within columns with the same letters are not signifi- cantly different at the 5% level. Percent values were transformed to the arcsine for statistical analysis. 33 Table 6. Rf values of the l4C-bentazon metabolites from the center leaflet of the first trifoliate soybean leaf. Metabolites Rf Ethyl acetate-soluble .33 Water-methanol-soluble A .00 Water-methanol-soluble B .12 Water-methanol-soluble C .31 Water-methanol-soluble D .40 14C-bentazon .67 34 .pcaom qu>HDomoHpmu Hmuou mo unmoumm mo mfiumu CH pmmmmumxw mum mmsHm>n .mHmemcm HMUHumHumum MOM mchonm on» on meHowmcmuu mum3 mwsHm> ucmoumm .Hm>mH wm man an ucmumMMHp wHucmoHMHcmHm uoc mum HmvumH mama on» suH3 mcEdHoo cHnuHs mammzm m v.MH n «.mH m N.MH m w.vm m m.h m h.m n m.m m n m.mm m w.h m m.mH m H.mm m «.m m H.h m m.N H 3.. 3; 2; 2; Amy 3. 3L Amwmg coamucmn mHnsHOmcH a 0 «MI. m ansHom :oHumuaw IUVH IHocmnumz mHnfiHOmlHocmnumS Imumumom Hanna uamfiuwmua am.ucmfipmouu nouns mane m can H .mmmH somnmom mumHHOMHuu umHHm may no umHmme umucmo map :H caumucmnlqu mo EmHHonmumz .h mHnma 10. 35 Literature Cited Anderson, R.N. 1971. Postemergence chloroxuron treatments on soybeans. Weed Sci. 19:219-222. Anderson, R.N., R. Behrens, D.D. Warnes and W.E. Nelson. 1973. Bromoxynil for control of common cocklebur and wild common sunflower in soybeans. Weed Sci. 21:103-106. Anderson, R.N., W.E. Tueschen, D.D. Warnes and W.E. Nelson. 1974. Controlling broadleaf weeds in soy- beans with bentazon in Minnesota. Weed Sci. 22: 136-142. Baldwin, F.L. and R.E. Frans. 1972. Soybean and weed response to dinoseb and chloroxuron applied t0pically. Weed Sci. 20:511-514. Fenster, C.R. and G.A. Wicks. 1972. Weed control in field beans in Nebraska. Proc. N. Cent. Weed Contr. Conf. 27:35-37. ' Gossett, B.J., L.R. Reinhardt and W.P. Byrd. 1972. Cocklebur control in soybeans with 2,4-DB and chloroxuron. Weed Sci. 20:489-491. ' Parachetti, J.V., R.W. Feeny and S.R. Colby. 1972. Preemergence herbicides plus postemergence chlorox- uron on soybeans. Weed Sci. 20:548-553. Wang, C.H. and D.L. Willis. 1965. Radiotracer methodology in biological science. Prentice-Hall Inc., Englewood Cliffs, New Jersey, 363 pp. Wax, L.M., R.L. Bernard and R.M. Hayes. 1974. Response of soybean cultivars to bentazon, bromoxynil, chlor- oxuron, and 2,4-DB. Weed Sci. 22:35—41. Weber, W.J., L. ChristOpher, J. Fulner, D. Haniford and E. Kessler. 1972. Efficacy of bentazon on burcucum- her and certain serious weeds in Indiana. Proc. N. Centr. Weed Contr. Conf. 27:29. Chapter 3 THE BASIS FOR BENTAZON SELECTIVITY IN NAVY BEAN, COCKLEBUR AND BLACK NIGHTSHADE Abstract The trifoliate leaf of tolerant navy bean (Phaseolus vulgaris L.) retained less bentazon (3-iSOpr0py1-lfl 2,1,3 benzothiadiazin-(4)BH-one 2,2 dioxide) than the unifoliate leaf, or the leaves from susceptible cocklebur (Xanthium pennsylvanicum Wallr.) and moderately susceptible black nightshade (Solanum nigrum L.) seedlings from foliar appli- cations. The 14C from l4C-bentazon applied to the foliage of black nightshade moved throughout the entire plant. In cocklebur, the 14C moved throughout the treated leaf, where- as, in the trifoliate leaf of navy bean, very little acro- petal movement occurred from the site of application. How- ever, in the unifoliate leaf of navy bean, acrOpetal and basipetal movement of 14C from the leaf was observed. The species differed in the 14C-metabolites formed from 14 C-bentazon l and 5 days after treatment. The rapid metabolism of bentazon in the trifoliate leaf of navy bean 36 37 appears related to tolerance. Introduction Bentazon is a potential postemergence herbicide for the control of broadleaf weeds in soybean (Glycine max (L.) Merr.) and navy bean not controlled by present preplant and preemergence herbicidesl (l, 2, 5, 6, 7). Cocklebur is susceptible, and black nightshade moderately susceptible to bentazon. Both frequently escape currently used control measures in these craps. Penner (4) related selectivity of bentazon between tolerant soybean and susceptible Canada thistle (Cirsium’ arvense L.) to less spray rentention on the leaf and a higher rate of bentazon metabolism in soybean. The purpose of this study was to determine the basis for the selectivity of bentazon between navy bean at two stages of growth and two weed species, cocklebur and black nightshade, by comparing spray retention on the leaves, translocation and metabolism of bentazon. Materials and Methods "Sanilac” navy beans, cocklebur and black nightshade were grown from seed in a Conover sandy loam soil in the greenhouse at 25 i 2°C with supplemental fluorescent light- ing. 1Wyse, D.L., W.F. Meggitt and R.C. Bond. 1973. New herbi- cides for navy beans. Research Report N. Cent. Weed Contr. Conf. 28:76-79. 38 For the Spray retention study, bentazon was applied at 2.24 kg/ha to cocklebur and black nightshade, having four to six leaves, and to navy bean having only unifoliate leaves or having both unifoliate and trifoliate leaves. After ben- tazon application, the leaves were immediately rinsed with distilled H20 and leaf area determined. The rinse was evap- orated to a 10 ml volume, acidified with 0.5 ml of concen- trated HCl and extracted twice with 10 ml of ethyl acetate each. The ethyl acetate fractions were evaporated to dry- ness ig_!§ggg, and the residue methylated in 1 ml of diethyl ether with diazomethane. The samples were then evaporated to dryness in 22329, resuspended in 0.5 ml of ethyl acetate, and 10 ul analyzed quantitatively by comparison to stan- dards with gas-liquid chromatography using a flame ioniza- tion detector and 4% SE-30 on gas chrom Q column. The tem- perature was 100°C, and the flow rate was 40 cc/min. Procedure for the translocation and metabolism part of this study were the same as those previously reported (3). A comparison was also made of the total amount of 14C 14C—bentazon in the leaf apices within each species with time. The total 14C was computed by summing the total amounts contained by the 14C-metabolites and that amount remaining as of the three solvent fractions, and that amount in the meth- anol-insoluble residue fraction. The 14C remaining as ben- tazon was the sum present in the three solvent fractions. Data presented in tables are the means of two experi- ments with three replications per experiment and three plants 39 per replication. Plants shown in figures are representative of two or more experiments. Results and Discussion The trifoliate leaf of navy bean retained significantly less bentazon on the surface than was retained on the uni- foliate leaf or the leaves of cocklebur and black nightshade seedlings (Table 1). These results indicate that differences in Spray retention may contribute to bentazon selectivity between species. More 14C was translocated both acrOpetally and basi- petally in unifoliate navy bean than in trifoliate navy bean (3). However, the 14C movement in black nightshade seedlings was much greater than either and translocated throughout the entire plant (Figure l). The movement increased with time. 14 In cocklebur, the C diffused acrOpetally throughout the entire leaf after 1 day (Figure 2). After 5 days the 14C accumulated in the leaf apex. As black nightshade is only moderately susceptible to bentazon, the extent of translocation does not appear re- 14C translocated C-bentazon, but rather, readily translocated 14C- lated to tolerance. It may well be that the is not 14 metabolites not found in either navy bean or cocklebur. The manner of bentazon metabolism in the unifoliate and trifoliate leaves of navy bean was similar (Table 2). How- ever, in the unifoliate leaves of navy bean, a significantly greater percentage of 14C remained as unmetabolized bentazon 40 after 1 day (Table 3). Bentazon metabolism in black night- shade differed markedly from that in navy bean (Table 2). There were a greater number of metabolites in the ethyl acetate-soluble fraction and the Rf values of metabolites in both the ethyl acetate-soluble and methanol-soluble frac- tions differed from those in navy bean. However, the percen- tage of 14 C remaining as unmetabolized bentazon was signifi- cantly greater than in the trifoliate leaf of navy bean after 1 day (Table 3). Additional bentazon metabolism occurred in black nightshade between 1 and 5 days after treatment. In cocklebur, more metabolites were also found 1 day after treatment than in the trifoliate leaf of navy bean- (Table 2). As in black nightshade, numerous metabolites from cocklebur differed from those found in navy bean be- cause of differences in Rf values and the greater quantity found in the ethyl acetate-soluble fraction. Again, the 14C remaining as unmetabolized bentazon was sig- percent of nificantly greater in cocklebur than in trifoliate navy bean after 1 day (Table 3). Although the number of metabolites found in cocklebur increased after 5 days, the percentage of unmetabolized bentazon was much higher than in the trifoliate leaf of navy bean after 5 days (Table 2), or in any of the other plant material studied (Table 4). 14C that accumulated in the leaf The total amount of apex was significantly greater in cocklebur than in the other three types of plant material examined both 1 and 5 days after treatment (Table 4). This accumulation coupled with 41 the slower rate of detoxication may also contribute to the susceptibility of cocklebur. There was very little difference in the amount of un- metabolized bentazon remaining between the leaf apex of the unifoliate and the trifoliate leaves of navy bean after 1 day (Table 4). Since the 14 C was translocated more readily in the unifoliate leaves than in the trifoliate leaves of navy bean, apparently the bentazon distribution was greater, and this may relate to the previously observed greater sus- ceptibility of navy bean treated when they had only the uni- foliate leaves . The greater bentazon retention on the uni- foliate leaves following postemergence applications may also contribute to the susceptibility. Comparing the total 14C and that amount remaining as unmetabolized bentazon in the leaf apex with time in each Species, only cocklebur Showed a significant increase in 14C and no significant change in 14C remaining as total bentazon after 5 days (Table 5). Trifoliate navy bean was found to be tolerant to foliar applications of bentazon apparently because of less leaf retention and translocation, and an initially faster rate of metabolism when compared with unifoliate navy bean, cocklebur and black nightshade. Black nightshade exhibited less susceptibility to foliar applications of bentazon than cocklebur. This could be par- tially attributed to the increased rate and extent of metab- l4 olism after 5 days. However, since significantly more C 42 remained as unmetabolized bentazon in the leaf apex after 5 days compared with that amount remaining in the trifoliate leaflet apex of navy bean, there probably were other factors contributing to selectivity. Extensive diffusion of bentazon throughout the leaf, slow metabolism, continued total 14C accumulation in the leaf apex to 5 days after treatment and greater spray retention by the leaves all may have contributed to the observed sus- ceptibility of cocklebur to foliar applications of bentazon. 43 Table 1. Leaf retention of bentazon after foliar applica- tion.a Species Amount retained (n moles/100 cmz) Navy bean unifoliate 1758 b Navy bean trifoliate 802 a Cocklebur 2167 b Black nightshade 2410 b aMeans within the column having identical letters are not significantly different at the 5% level. a... .... C . . ... 3 ... . . I. .u.. . _ I I . . .. . .— _ I .. .-. . v _ .. . . E “a .: I ... S .9 . . H . .h .n ... .\. .. a a. 2. “ ‘ ... .. ... ... T ... ... I I Z . \ ... . . t . ». ... . ... : 3. . . — u . . . . ...... _ .. . “ ... 3 . .. . . .‘. ... .: l I . . . . : I ... I ... .u ... .. .2 . . .. ..fi . . “ .. .\. .. _ ... ... “ . . . . ... .. ~m~ : I . . 5 ... ... .... .- .. ... e.\ . . u ... I 3 . . . . .\. . e . ... ... ~—. . . .. u H _ .. ... .. I ... .: . . ~_. .. ‘ ... ... ..- .: .: ... T. .. ... .u ... . .. . . .s . I .. _ c. ... . s o . ... .H. . . 5 A . W. S ... C ... I .\. a u o . .o q . a . T . ‘. I ‘ a. .o . ..u H \ ~ .. ... C ... 3 s ‘ . \ ~ . . . ... . . _ . . . ... ... .x. . \ a \ . . . . Jhs . . ... w“ “a. ... ea. « .. I 5 E 45 46 Figure 2. Translocation of l4C-bentazon in cocklebur. The treated plants (A) and the corresponding radio- autograph (B) show cocklebur with four to six leaves harvested 1 day after foliar application. The treated plants (C) and corresponding radio— autograph (D) show cocklebur at the same stage of growth harvested 5 days after foliar application. 4? 48 0.0a 0.00 00. 0.00 0.H0 00. 0.0 0.00 0.0 0.0m 00. nonwuamm 0.0 0.0 00. 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N09 H 0.050500000 00um0 w>00 m 050 H ©0um0>00£ 0000000 p50Hm 050000> no 000000 m00H 5003000 50000500 U0NHHon0u0E5D 050500800 050 0x0um5 5000050QI00H mo 5000000500 .0 0HQ0B 51 .H0>0H 0m 000 00 050000000 >H05000005000 000 0555H00 000000 0 00 000555 0500 000 0003 0300 500003 050020 00000 00000.0 0.00 000.00 «0000.0 0.00 000.0 -00005 00000 000.00 0.00 0000.00 000.0 0.00 0000.00 050000000 0000000000 000 0.0 000.0 000 0.00 000.0 0000 0>0z a... 02.. 0000Hom055 000 0.0 000.0 000 0.00 000.0 0000 0>0z I. 02.. 05 000\000o5 0. .0. .05 000\000o5.m. .05 000\m00o5 0. .0. .05 000\00005 0.. 50000500 ©000Ho000055D H0009 50000500 ©000Ho000055D H0009 00000mm M00 m M00 H 0.050500000 00000 0000 m 050 H 0000000 050Hm 050000> 00 000000 m00H 5000 50000500 0000Ho0000555 050500500 050 50000H555000 50000500I00H H0000 00 5000000500 .m 0H00B 52 Literature Cited Anderson, R.N., W.E. Lueschen, D.D. Warnes and W.E. Nelson. 1974. Controlling broadleaf weeds in soy- beans with bentazon in Minnesota. Weed Sci. 22: 136-142. - Fenster, C.R. and G.A. Wicks. 1972. Weed control in field beans in Nebraska. Proc. N. Cent. Weed Contr. Conf. 27:35-37. Mahoney, M.D. and D. Penner. Bentazon translocation and metabolism in soybean and navy bean. Weed Sci. (In preparation). Penner, D. 1972. Selectivity of bentazon between soy- bean and Canada thistle. Proc. N. Cent. Weed Contr. Conf. 27:50. Wax, L.M., R.L. Bernard and R.H. Hayes. 1972. Response of soybean varieties to bentazon. Proc. N. Cent. Weed Contr. Conf. 27:28. ‘ Wax, L.M., R.L. Bernard and R.M. Hayes. 1974. Response of soybean cultivars to bentazon, bromoxynil, chlor- oxuron and 2,4-DB. Weed Sci. 22:35-41. Weber, W.J., L. ChristOpher, J. Fulner, D. Haniford and E. Kessler. 1972. Efficacy of bentazon on burcucum— ber and certain serious weeds in Indiana. Proc. N. Cent. Weed Contr. Conf. 27:29. Chapter 4 SUMMARY AND CONCLUSION Greenhouse and laboratory studies were conducted to examine spray rentention, translocation and metabolism of bentazon in seedlings of navy bean at two stages of growth, cocklebur and black nightshade. Studies were also con- ducted to examine bentazon translocation and metabolism in soybean. The trifoliate leaves of navy bean retained less ben- tazon, metabolized 14C-bentazon faster and showed less movement of 14C from the site of application than the uni- foliate leaves of navy bean, and the fourth leaf from the seedlings of cocklebur and black nightshade after 1 day. All of these factors appeared to play a role in the tolerance of navy bean to foliar applications of bentazon. Navy beans, with prior treatment of EPTC, chloramben and trifluralin, did not decrease the rate of bentazon metabolism. Only the ‘trifoliate leaves of navy beans receiving prior treatment of EPTC showed greater translocations of 14C. Navy bean tol- erance to bentazon was not affected. 14 Greater translocation of C and an increase in the amount of bentazon retained on the surface of the unifoliate 53 54 leaves of navy bean appeared related to injury by foliar applications of bentazon at that stage of growth. Continuing bentazon metabolism 1 to 5 days after treat- ment offers a partial explanation why black nightshade was only moderately susceptible. Other factors may also have contributed to the observed tolerance of this species to bentazon since there was a significantly greater amount of 14C-bentazon in the leaf apex of black nightshade than in trifoliate navy bean. Increased spray retention, more extensive acrOpetal movement, a slower rate of metabolism and a greater amount 14C remaining in the leaf apex l and 5 days after foliar of applications of bentazon appeared related to cocklebur sus- ceptibility to bentazon. Translocation was more extensive and the rate of metab- olism was slower in soybean than in navy bean after 1 day. Other factors not studied may also have contributed to the tolerance of soybean to foliar applications of bentazon. Soybean harvested at maturity contained no l4C-bentazon. Four apparent l4C-conjugates of bentazon were isolated with molecular weights ranging from approximately 269 to 698. 10. ll. 12. 13. 55 LIST OF REFERENCES Abernathy, J.R. and L.M. Wax. 1973. Bentazon mobility and adsorption in twelve Illinois soils. Weed Sci. 21:224-227. Anderson, R.N. 1971. Postemergence chloroxuron treat- ments on soybeans. Weed Sci. 19:219-222. Anderson, R.N., R. Behrens, D.D. Warnes, and W.E. Nelson. 1973. Bromoxynil for control of common cocklebur and wild common sunflower in soybeans. Weed Sci. 21: 103-106. Anderson, R.N., W.E. Lueschen, D.D. Warnes and W.E. Nelson. 1974. Controling broadleaf weeds in soybeans with bentazon in Minnesota. Weed Sci. 22:136-142. Baldwin, F.L. and R.E. Frans. 1972. Soybean and weed response to dinoseb and chloroxuron applied topically. Weed Sci. 20:511-514. < Feeny, R.W., J.V. Parochetti and S.R. Colby. 1974. Selective action of chloroxuron on soybean and tall morning glory. 1974. Weed Sci. 22:143-150. Fenster, C.R. and G.A. Wicks. 1972. Weed control in field beans in Nebraska. Proc. N. Cent. Weed Contr. Conf. 27:35-37. Gossett, B.J., L.R. Reinhardt and W.P. Byrd. 1972. Cocklebur control in soybeans with 2,4-DB and chlor- oxuron. Weed Sci. 20:489-491. Hicks, D.R., J.W. Pendleton, R.L. Bernard and T.J. Johnston. 1969. Response of soybean plant types to planting patterns. Agron. J. 61:290-293. McWhorter, C.G. and E.E. Hartwig. 1972. Competition of johnson grass and cocklebur with six soybean vari- eties. Weed Sci. 20:56-59. Parochetti, J.V., R.W. Feeny, and S.R. Colby. 1972. Preemergence herbicides plus postemergence chloroxuron on soybeans. Weed Sci. 20:548-553. Penner, D. 1972. Selectivity of bentazon between soy- bean and Canada thistle. Proc. N. Cent. Weed Contr. Conf. 27:50 U.S. Department of Agriculture. 1965. Loses in Agri- culture. Agr. Handb. No. 291:120. 14. 15. 16. 17. 18. 19. 20. 56 Wang, C.H. and D.L. Willis. 1965. Radiotracer metho- dology in biological science. Prentice-Hall Inc., Englewood Cliffs, New Jersey, 363 pp. Wathana, 8., F.T. Corbin, and T.W. Waldrep. 1972. Absorption and translocation of 2,4-DB in soybean and cocklebur. Weed Sci. 20:120-123. ' Wax, L.M., R.L. Bernard and R.M. Hayes. 1972. ReSponse of soybean varieties to bentazon. Proc. N. Cent. Weed Contr. Conf. 27:28. Wax, L.M., R.L. Bernard and R.M. Hayes. 1974. Response of soybean cultivars to bentazon, bromoxynil, chlor- oxuron, and 2,4-DB. Weed Sci. 22:35-41. Weber, C.R. and W.H. Fehr. 1966. Seed yield losses from lodging and combine harvesting in soybeans. Agron. J. 58:287-289. Weber, W.J., L. ChristOpher, J. Fulner, D. Haniford and E. Kessler. 1972. Efficacy of bentazon on burcucumber and certain serious weeds in Indiana. Proc. N. Cent. Weed Contr. Conf. 27:29. Wyse, D.L., W.F. Meggitt and R.C. Bond. 1973. New herbicides for navy beans. Research Report N. Cent. Weed Contr. Conf. 28:79-79. llllllIII'i