“—7.15ka Michigan State University This is to certify that the dissertation entitled The Basis and Reversal of Na-Bentazon Antagonism on Sethoxydim Absorption and Activity presented by Gunawan Wanamarta has been accepted towards fulfillment of the requirements for Ph.D. . Crop and Soil Sciences _— degree in ____ Major professor I May 1 3 , l9 8 7 Date uen- 1::— - A - '- -:L 1 n 1 A 0-1277! _ Ilflifllfl'emllll'lfllfl’l‘l'flfllmflIIIIII'IWIWII l“ 3 1293 01750 5417 RETURNING MATERIALS: iV1ESI.J Place in book drop to ngpARIEs remove this checkout from “3—. your record. FINES will be charged if book is ‘ returned after the date Hi stamped below. ‘\ THEE-g) 'a :2004 THE BASIS AND REVERSAL OF NA-BENTAZCN AN'I‘ACXXVISM ON SEI‘HOXYDIM ABSORPTIG‘J AND ACTIVITY GtmawanWanamarta A DISSERTATION! Submitted to Michigan State University in partial fulfilment of the requiranents for the degree of WOFPHIIDSOPHY Department of Crop and Soil Sciences 1987 ABSTRACI‘ THE BASIS AND REVERSAL OF Na-BENTAZW ANTAWISVI m SEITDXYDIM ABSORPI'ICN AND ACTIVITY By Gunawan Wanamarta Various experimental adjuvants, including surfactants, pareffinic oil and soybean oil based crop oil cancelitzrates ((130), were tested to maximize the herbicidal activity of settmydim {2[1-(ethoxyimim) butyl] -5-{2-( ethylthio ) -3—hydrmcy-2-cycld1exen-1—axe} and bentazon [3-isoprcpyl-1H—2, 1 , 3—benzothiadiazine—4( 31-!)-cne 2,2- dioxide]. Identification of superior adjuvanm was dcne by measuring the effects of these experimental adjuvants on herbicide spray droplet spreadability and 14C-her’oicide absorption on target weed leaves. A direct correlation between the effects of adjuvants on spray droplet spreadability and l4C-herbicide absorption was observed for bentazon, but not for sethoutydim. Thus, screening adjuvants based on droplet spread measurenent was only useful for bentazcn. A superior surfactant for sethoxydim, the surfactant D7, was identified by measm‘ingMC-setlmydimuptakebyquackgrassleavesaftermh. When surfactants were blended with paraffinic oil or soybean oil to form a crop oil concentrate (CDC), the efficacy of the surfactant alone was not necessarily related to the efficacy of the CDC. The Inter. also 39111: £01m reac’c acich 908811 beta ’A Na‘ber efficacy of a (DC as an adjuvant was influenced by the herbicide, the type of oil, and the type of surfactant added to the oil. In field evaluations, several superior adjuvants identified in fine laboratory enhancedsetrmcydimandbentazonactivitiesonthetargetweeds. Interaction between surfactant arnd oil types on adjuvant efficacy was also apparent. Scanning electron microscopy (SEM) stoned the ability of several surfactants, including D7, to alter or solubilize the epicuticular wax (m) of quackgrass leaf cuticles. The effects of surfactants on m solubilization was not always related to l4C-sethoxydim absorption. Little relationship existed between wetting characteristics and 14C—sethoxydim absorption. Oorbination of sethoutydim with the Na—salt of bentazon reduced the activity of sethoxydim on quackgrass control in the field by reducing the uptake of sethoxydim. The reduction in 14C-sethoutydim absorption was attributed to the formation of a more polar Na-salt of sethonnydim. AnenrchangereactionbetweennNa+ ionsinthebontazon formulation and the 14" ions at the hydroxyl group of sethoxydim is proposedasthemechanismfortheinteraction. Thisexchange reaction, however, was prevented by the addition of varions organic acids. Cations, such as Na+, 1.1+, K+, cs“, Ca“, arnd Mg“, when associated with a weak acid, also produced similiar antagonisn possibly through the sane mechanisn of reaction as the Na-salt of bentazon. Severalwaystoecomnicallyoverootetheantagonisnof Na—bentazon on the herbicidal activity of sethoocydim were found. Addition of a specific surfactant, D7, at 2.4 L/ha coupletely overoonefineantagonisnonsefinxydimabsorptionandsefinmcydim activity in the field. Addition of various inorganic amoniun salts, such as anmoniun sulfate, annmiun phosphate, or annoniun nitrate to the spray mixture or replacement of Na formulated bentazon wifin bentazon formulated as the NH4-salt prevented the antagonism fron occuring. It is proposed that fine NH4-salts or the M-I4-fornnnlated bontazon prevented fine antagonism by forming fine Nl-I4-sa1t of sefincmydimandinfinisform, fineuptakeofsefinxydimbyfine quackgrass leaves was not inhibited. Field data on quackgrass control support fine laborame l4C-herbicide absorption studies . pmfes ACKMMLEDGEMENI‘S The aufinor wishes to express his sincerest gratitude to his major professor, Dr. Donald Penner, for his support arnd guidarnce throughout finese studies and for fine considerable time arnd effort he devoted during fine preparation of this dissertation. Sincere finanks are also offered to Dr. James Kells for his assistanceinthefieldaspectsoffineresearoh. Theassistanceof Drs. M. John Bukovac and Stanley Flegler is gratefully admowledged. AspecialfinarflcsisalsoextandedtograduatesfindentsBobStovicek, Rufin Shaffer, and technician Frank Roggenbuck for making my student years enjoyable. Finally, I wish to acknowledge the generous financial support of myparents, finepatientandmoral supportofmywife, duringmy extended student career. LIST C LIST C INFROI G‘API’E H'fl’TH‘fu TABLE OF CDNTENI'S Page LIST OF TABLES ........................................... . . vii LIST OF FIGURES ............................................. x1 WIW 000000000000000000000000000000 O O O O O O ........... 1 CHAPTER 1: FOLIAR ABSORPTICN, A LITERATURE REVIEW .......... 3 I. MED'IANISM OF ABSORPTIO‘I ............... . ......... 3 II. SPRAY SOLUTICN ................ . ...... . . . . . ...... 9 III. PLANTLEAFFACIORS ................ . ......... .... 20 IV. WWAL mm 0 O O O O O O O O O ..... O O O C O O O O O O O O 27 LITERATURE CITED . . . . . ................................. 33 Q-IAPI'ER 2: IDENTIFICATIGNI OF SUPERIOR ADJUVANTS FUR SETI-DXYDIM AND BENTAZON .......... . ............. 46 ABSTRACT .............................................. 46 INTRGIXLTICN . . ..................... . . . . . ..... . ....... . 48 PETERIALS AND MED-IDS .............. . . ...... . .......... 40 RESULTS AND DISQISSIO‘J ...................... . ......... 51 LITERATURE CITED .......... . ........................ . . . 70 O-IAPI'ER 3: THE BASIS OF BENTAZO‘I ANTAGIVISM m SEIT'DXYDIM ABSORPTIGVANDACI‘IVITY .......... . ...... ....... 73 mm OOOOOOOOOOOOOOOOOOO O O O O O O O O C O O O O O O O O O O C O 0 O O O O O 73 WIm ...... O O O ...... O ...... O ........ O O O O C O O O O O O 75 mm m m C ....... O O O O O O O C O O O O O O O O O O ....... W RESULTS AND DISOJSSIW . . ......... . .......... . . ........ 81 LIMAME CITE ......OOOOOOOO.......OOOOOOOOOOOOOOOOO 98 CHAPTER 4: W THE ANTAGX‘IISTIC EFFECT OF Na-BEN'I‘AZON m SEI'HOXYDIM ABSORPTION AND ACTIVITY ........... 100 ABSTRACT .. ............................................ 100 INTRCDUCTIW ............... . .......................... 102 MATERIALSANDMETI-IDS .............. . ............. ..... 104 RESULTSANDDISQJSSICN .............. .................. 106 LITERATURE CITED ... ................................... 119 CHAPT filth? APPEb LIST CHAPTER 5: MUM OF SURFACTANTS (1‘1 W8 EPICU'TICIJLAR WAX AND ITS RELATIONSHIP WITH SPRAY DROPLET SPREAD- ABILITY AND 14C-SETI'DXYDIM ABSORPTION ........ 121 ABSTRACT ............................. . ................ 121 INTRCDUCTICN ................................... . ...... 123 mms m ms 0 O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O C O 125 RESULTS AND DISCIJSSICN ................................ 127 LITERATURE CITED ...................................... 143 SID/MARY AND (DNCLUSIG‘J ..................................... 145 APPENDIX .................................... . . ............. 147 LIST OF REFERENCES ......................................... 173 ...—J 10. Pa LIST OF TABLES GIAPTERZ Effect of several selected experimental adjuvants on sefino-rydim activity in fine field in 1985 ...... . . ........ Effect of selected adjuvants on bentazon activity at 0.11 kg/ha in fine greenhouse ........................ Effect of selected experimental adjuvants on bentazon activity in the field in 1984 .......................... Effect of selected experimental adjuvants on bentazon activityinthefieldinl985 .............. ..... CHAPTER3 Effects of darkness, sequential, and separated applic ations of Na-bentazon on sefinoxydim and Na-bantazcn interaction ...................................... Effect of renoval of epicuticular wax on quackgrass leaves with chloroform on sefinoxydim and Na-bentazon interaction ....... ............................ Diffusion of l4C-sefinoxydim through isolated tonato fruit cuticle ................. Diffusion of 14C-bentazon finrough isolated tonato fruit cuticle ........ ...... EffectofNa—bentazononsefinxydimpolarity ...... Effect of Na-salts of strong and weak conjugate base on l4C-sefinoxydim absorption ...................... Effect of bentazon fornnnlations on l4C-sethoxydim W“! O O O O OOOOOOOOOOOOOOOOOOOOOOOOOOOOOO O O ..... Effects of several monovalent and divalent cations on 14C-sethourydim absorption ..................... Effect of organic acids on sefinoxydim and Na-bentazon interaction .. ........... . ....... ......... Effects of Na-bentazon, Na-acetate, and Ca-acetate on sefincntydim activity in fine field in 1986 ....... . . ...... GIAPTER4. Effects of fine surfactant D7 and NH4-bentazon on sefinoxydim and Na—bentazon interaction ..... . ........... Effectsofseveralannoniunsouroesonsefinoxydim and Na-bentazon interaction . ........ . ..... . ........ Effect of spray solution pH on sefinoxyditin and Na-bentazon interaction ..... ................ viii 67 68 69 87 89 92 93 94 95 96 110 112 l c 10. ll. 12. 4. Effect of bentazon formulation and amoniun sulfate on sefincnnydim polarity . ................. ....... 113 5. Effects of emonium sulfate, alumina hydroxide, and sodiun hydroxide on sefinoxydim absorption .......... 114 6. Influence of fie D7 surfactant and inorganic salts onfinecontrol ofquadcgrasswifinsefinoxydimand Na—bentazon mixture in 1985 arnd 1986 ................... 115 7. Influence of sefinoxydim and D7 surfactant on bentazon activity in fine field in 1985 ................ 116 8. Influence of D7 surfactant and inorganic salts on sefinoxydim absorption in sefinoxydim—bentazon- acifluorfen mixture ................................... 117 9. Influence of bentazon and acifluorfen on fie control of quackgrass with sefinoxydim in fine field in 1986 118 CHAPTER 5 1. Effect of various adjuvants on epicuticular wax of quackgrassleaf cuticle afterlh . ...... ........ 132 APPENDIX 1. Effect of surfactants as spray adjuvant on droplet spread and 14C-sefinoxydim absorption on quackgrass 147 2. Effect of soybean oil concentrate (SOC) as spray adjuvant on droplet spread and l4C-sefinoxydim absorption on quackgrass ............... . .. ............ 150 3. Effect of paraffinic oil concentrate (POC) as spray adjuvant on droplet spread and l4C-sefinoxydim absorption on quackgrass ......... . . . .. ...... . ........ 153 4. EffectoffieEandFseriesPOCasadjuvanton droplet spread and l4C-sefincxydim absorption on quackgrass ......................................... 156 5. Effect of surfactants as spray adth on droplet spread and 14C-bentazon absorption on cannon lanbsquarters ......................................... 158 6. Effect of paraffinic oil concentrate (POC) as spray adqu on droplet spread and 14C-bentazon absorption on comm lambsquarters .............................. 160 7. Effect of soybean oil concentrate (SOC) as spray adjuvant on droplet spread and l4C-bentazon absorption on cannon lanbsquarters ............................ 162 8. Effect of selected adjuvants on bentazon activity at 0.28 kg/ha on lambsquar‘ter in fie greenhouse ......... 164 9. Effect of selected adjuvants on bentazon activity at 0.56 kg/ha on lambsquarter in fie greenhouse ......... 165 10. Effect of fie C-series surfactants on sefinoxydim and Na-bentazon interaction .......................... 166 11. Effect of fie BWC-series surfactants on sefinoxydim and Na-bentazon interaction .......................... 168 12. Effect of fine GEN-seriee surfactants on sefinoxydim and Na-bentazon interaction .......................... 170 13. Effect of fie surfactant D7 rates on sefinoxydim and Na-bentazon interaction .......................... 14. Effect of bentazon formulation arnd anmoniun sulfate onsefinoxydimactivityinfiegreenhouse ............. LIST OF FIGURES CHAPTER 2 1. Relationship between droplet spread and 14C-sefinoxydim absorption on quackgrass as influenced by adjuvante.... 2 . Relationship between droplet spread arnd 14C-bentazon absorption on lambsquarter as influenced by adjuvants.. CHAPTER 3 l. Absorptionof 14C-sefinoxydiminfiepresenceand absence of Na-bentazon ............................. 2. UV Spectra of sefinoxydim, Na-bentazon, arnd fie mixture of sefinoxydim and Na—bentazon ............ CHAPTER 5 l. Scanningelectronmicrografinsofquackgrassleaf enrfaces treated with (a) distilled water, (b) chloroform, ( c) sefinoxydim solution wifinout adjuvant added and (d) 1.2 L/ha of D7 surfactant solution ...... 2. Scamningelectronmicrcgraphs chuackgrassleaf surfaces treated with 0.56 kg/ha sefinoxydim arnd 1.2 L/ha D7 surfactant solution for (a) 1 h, (b) 5 h, (c) 24 h, and (d) 30 sec ........... ...... 3. Scanningelectronmicrographs ofquackgrassleaf surfaces treated wifin 0.56 kg/ha sefinoxydim solution containing 1.2 L/ha (a) D7 surfactant, unrinsed, (b) A29 enrfactant, (c) A17 enrfactant, (d) A49 surfactant ...... ............... 4. Scanningelectronmicrcgraonsofquackgrass leaf surfaces treated wifin 0. 56 kg/ha sefinoxydim solution containing (a) 1.2 L/ha A52 surfactant, (b) 2.4 L/ha (DC, (c) 1.2 L/ha A41 surfactant, and (d) 1.2 L/ha A51 surfactant ................... 5. Scanningelectronmicrographs ofquackgrass leaf surfaces treated with 0.56 kg/ha sefinoxydim solution containing 1.2 L/ha (a) A5 surfactant, and (b) A39 enrfactant ............... . ................ page 66 86 91 133 135 137 die: for INTRGIJCTION Most postenergece lerbicide applications contain adj uvants in fie spray solution. (1e or more adjuvants or enulsifiers may be included in fie terbicide formulation and additional adjuvants may be added to fie spray solution by fie applicator. 'Ii‘erehavebeennuteronsstudiesonfieeffecteandfmctionsof adjuvants. that report finat adjuvants increase lerbicide efficacy. Functions of adjuvants include increasing foliage wetting and coverage, solubilization of fie leaf epicuticular wax, and irncreasing lerbicide penetration. I-lmever, fie mechanisms involved in fie latter two are not fully understood. Seficxydim {2[1-(efinoxyimino)butyl]-5-[2-(efiny1finio)DIUPY1J-3- hydroxy-Z-cyclotexen-l—oe} is a relatively new postemergece grass herbicide foruse in soybeans(G1ycinemax L. Merr.) andofier dicotyledonous crops. 'Ite label reconnends finat adjuvants be added for postenergece seficxydim applicatioe. 'Iteuptakeof sefinoxydimwificut adjuvantis lowandfieaddition of comercial adjuvanm increase fie uptake of sefinoxydim. 'Ite identification of new arnd superior adjuvante finat can increase fie uptakeofseficxydimtoalevelhigherthanfinatobtainedwifin existing comercial adjuvante will enhance seficxydim efficacy. Tank—mixing two or more terbicides controlling different WV. Emu differingweedspectrunisacomcnandpopularweedcontrol practice. Severaladvantagesoftank-mixingincludeanincreasedin weed control spectrum, less trips across fie field, and less expenditures on labor and equipnent. 'n‘erehavebeenmneronsreportsfinattankmixingncstoffienew postemergerce grass lerbicides, including sefinoxydim, wifin a postenergece broadleaf lerbicide such as bentazon [3-isopropyl-1H— 2,1,3-benzothiadazine—4(3H)—oe 2,2—dicxide] may reduced fie activity of fie grass terbicides. Elucidation of fine basis for fine interaction betweenseficxydimancbentazonisimportantinfindingnevwaysto overconefinisantagonisnsofinattankmixingoffiesetwoterbicides can be acconplisted wifinout antagonism. 'Ileobjectives cffineresearohvere: (1) tofindasnperior technique for rapidly evaluating experimental adjuvants and to use fine technique to identify superior adjuvants, (2) to determine fie basis of Na-bentazon antagonism on sefinoxydim absorption and activity, (3) tofindwaystooveroorefieantagonisnofNa-bentazon, and (4) to determine wrefier fie effects of surfactants on spray droplet spreadability, cuticle, and l4C-rerbicide absorption were related. fa ch 19 GIAP'TERl mLIAR ABSORPTIO‘I I. Mechanism of absorption. The absorption of pesticides applied to fie foliage of plants is influencedbyseveral factors. Ttesefactorscanbecategcrizedinto three major groups including: (1) fie properties of fie pesticide arnd fie spray solution, (2) fie properties of fie plants foliage, (3) the enviromental conditions in which fie plants are treated. 'I'tese factorswillbediscussedinmoredetail. For a foliar applied pesticide to exert its activity, fie chenical Inclecules nust enter fine plant cells finrough a series of clenically and structurally differing layers. 'Ihese layers are locwn as fie cuticle, fie cell wall, and fie plasmalenma (Bayer and Lamb, 1973). 'ne mechanism of chemical peetration into fiese layers will be discussed separately. A. Cuticular peetration 'I'te plant cuticle consists of layers of waxes, pectin, cutin, and cellulose. ‘ITe structure of cuticle has been proposed to resemble a spogeinwhichfiefraneworkisrepresentedbycutinandfiercles are filled with wax platelets. 'I'te holes oriented toward fie outer surface may be filled predominantly with wax, while more pectic and cellulosic substances are found toward fie innner area. 'I'rerefore, 4 fiereisagradientfronlowpolarityatfieexternalsideoffine cuticle to high polarity at fie internal side of fie cuticle next to fie epidermal cell walls (Van Overbeek, 1956; Muzik, 1974). In geeral, fie peetration of chemicals through fie cuticle is fie rate limiting step in foliar absorption, and fie epicuticular wax layer imposed a major barrier to fie movement of foliar applied chenicals (Bukovac, 1965; Hull, 1970; Baker and Bukovac, 1971). 'I't'e absorptive pafinways of lerbicides finrongh fie plant cuticle are hypofinesized to be different for polar annd non—polar corpounds. Polar materials will enter fie plant cuticle preferentially via aqueons (hydrophilic) routes, while fie non-polar conpomd enter via lipoidal (lipqinilic) routes (Craft annd Foy, 1962; Martin annd Juniper, 1970). Since fie diffusing chenical molecules will be partitioed between fie lipid and fie aqueons components of fie cuticle, it is speculated finat no oe route will be exclusive (Price, 1982). The movement of chemicals across fine cuticles is a simple diffusion processduetofieabseceof livingcellulartissmeinfiecuticle (Price, 1974). The rate of peetration of a chenical mlecule finrough fie cuticle is influeced by several parameters such as fie cocentration of chemicals ontside annd inside fie cuticle, fie diffusion coefficient of fie chenical in lipid, fie thickness of fie cuticle, annd fie partition coefficients of fie chemicals in external/ lipid annd lipid/aqueous interfaces (Price, 1982). Tie diffusion coefficient of a chemical is influeced by its molecular size, temperature, and fie viscocity of fie cuticle (Price, 1982). 'I‘l'e ultrastructure annd orientation of the n) epiantiallar wax also agnears to influence absorption (Norris, 1974: Price, 1982). Foliaruptakeoffienonpolarconpomdshavebeenpropcsedto ocarrviaadirectpafinwayinvclving (1) sorptionintofieouterwax layer, (2) passage finrough fie cutianlar menbrane, and (3) desorption into fie apoplast (Price, 1982). 'I'ne latter step has been found to limit fie foliar uptake of several herbicides (Hanilton et al., 1982; Richard and Slife, 1979). Foliar uptake of polar couponnd finrough fie aqueous (polar) pafinway has been fie subject of much speculation (Price, 1982). Plants wifin adequate moisture supply or in high humidity enviroment will have hydrated cuticle (Van Overbeek, 1956). Under finese conditions, fie lipcpnilic waxes will be spread apart facilitating absorption of polar corpounds (anik, 1974; Vann Overbeek, 1956). Men plants areundermoisture stress, fieantinwill bedehydrated. Tie waxy units will be pulled closer together, annd finis will reduce fine permeability of fie article to polar conpamds. However, a non-polar (lipophilic) pafirvay through fie waxy portion of fie article is still available for a relatively non-polar rerbicide to peetrate. Hoch (1979) observed strands of polysaccharide microfibrils in fie leaf cuticle of malus (Malus pumila) plants that originated at fine epidermalcellwallandentendedtofieantinmatrix, andinsone cases to fie article surface. He suggested finat fiese polysaccharide microfibrils strannds provided a specialized hydrophilic pafinway for polar dnemicals. 'I'te ncvement of flamprop-mefinyl [nefinyl-N-benzoyl-N-( 3-chloro-4- f1uorcptenyl)-2—aminopropionate] between spray droplet and fie wax surface was studied by Hamilton et a1. (1982). They ford fie maximum movenentoffiechemical intofinewaxccalrredduringfiepericdjust prior to fie total evaporation of fie applied droplet. 'I'tecuticlehasbeenreportedtopossessanetnegativecharge onfiesurfaceardexhibits cationexchargepropertieswhichmay influece fie diffusion of chemicals. 'Ite dissociation of fie acidic residuesinfieantinwasfoundtoberesponsible forfinisanticle property (Yamada et al., 1964). Due to its charge, perneability of isolated articles to catioe was far greater finan for anions (Yamada et al, 1964). Recently, Price (1982) was able to identify hydrolizing enzyme located in fie cuticle that can hydrolize esters. He speculated finat this enzyme may be able to facilitate fie diffusion of conpounds wifin high moleanlar weight by hydrolizing it to snaller fragnents. It alsomayinvolvedinhydrolysisofphecxyestersandfieester portion of graninicides such as diclofop—nefinyl [mefinyl 2- [4-(2,4- dichlorqinenoxymi‘flmflmate). B. Cell wall penetration 'Ilecellwallisfiesecondbarriertofieabsorptionof chemicalsbyfieplant leaves. Thecellwall isconposedofadense network of cellulose and renicellulcse microfibrils wifin inter- fibrillar spaces finat are commly filled with water (Bayer and Lumb, 1973). The cell wall, unnlike fie cuticle, is known to offer little 7 resistance to pesticide penetration. Onenicals will penetrate the cell wall by diffusion. Cell walls have hydrophilic properties and a high cation exchange capacity due to fie acidic gronps of cellulose, henicellulcse, and pectin. It is fierefcre speculated finat it may be more difficult for non-polar denicals to peetrate finrough fie cell wall finan through fie anticle (Frannke, 1967). Ttecell wall alsomayactasamoleanlarsieverestrictingfie passageof chenicalnclealleswhosesizeexceedsfiediameterof interfibrillar spaces. Franks (1987) in his review, speanlated finat fiesubuicrcscopicchannelslefanndinfiecellwall, whichrecalled ectcdesmata, provideadinectpafinwaybetweenfieinnersurfaceoffie article and fie plasmalenma for chenical ncleanles to move firragh fine cellwall. Hereasoedthatfiepreferential sitesofuptakeof chemicalsccrrespodswell wifinfinesitesinwhichectodesnataare fond nest abundantly, such as fie walls of guard cells, cells surrounding fie vascular tissue (leaf veine), epidermal cells of trichones and hairs, and fie anticlinal side of epidermal cells. C. Plasmalenna peetration 'Ileplasmalenmamenbraneisfiefinirdardfinalbarriertofie absorption of chenicals by fie plant leaves. Little is kncm abont fie mechanism involved in fie movement of pesticide molealle across fie plasnalenma (Beyer and Lumb, 1973). 'Ile peetration of chenical moleanles finrough fie plasmalenna may require energy and possibly a carrier. According to Hull (1970), fie types of resistance finat will be 8 experienced by a petetrating chemical molecule finrough mm includes (1) resistanceinpassingfronaqueousphaseintofie membrare, (2) diffusion resistance wifinin fie menbrare, (3) resistance inpassingfronfiemenbrareintofieseoondaqteolsnediun. Several studies indicated that leaf absorption of organic chemicalsisanactiveprocessfinatrequireetergymanimlraand Goodnan, 1964; Jyung and Wither, 1964; Saunders et al.,1966; Kannan and Wither, 1967). To demonstrate fie existence of active uptake, Bayer and Lunb (1973) suggested five criteria finat reed to be satisfied, finat is (1) fie uptake of a chenical must have touperature coefficiont (QlO) greater than 2; (2) fie uptake is inhibited by anaerobic conditions, by inhibitors of respiration and ofier metabolic processes; (3) show a oonpetitive inhibition when similar compound is present; (4) transport across concentration gradient; and (5) fie rate of uptake can be hyperbolic. Kamimra and Goodnan (1964) reported finat foliar absmpuon of antibiotics was inhibited by pahotosynfiesis and respiration inhibitors such as 2,4-DNP (2,4-dinitrophenol) and arsenite. Jyung and Wittwer (1964) also reported similar observation wifin rubidiun ions. Saunders et al. (1966) observed fie uptake of phonoxy acetic acid (POA) was inhibited by low tenperature, anaerobic conditions, and 2,4-DNP. re] PO] 1i; lip (S7 9t. met} P. ‘t II . Spray solution A. Herbicide Properties of fie l'er’oicide may also influence its absorption. 'nese include molecular size and weight, polarity, and formllation. Tte effect of each individual characteristic on fie absorption process will be discussed separately. Properties of rerbicides which may indirectlyinfluonoeitsabsorptionbeleviorsarevaporpressureand photodecorposition. 'I'tesetnnfactorsreducefieamrtofherbicide available for uptake by fie leaves (Hull et al.,1982). l. Polari Ingeteral, duetoahighwaxcontent infieplant cuticles, a relatively non-polar oonpound wifin soni-lipophilic characteristic will penetrate fie olticle more easily finan polar ooupound (Hull, 1970). However, several studies indicated finat fie relatioehip between polarity and absorption is more oouplex. 'I're poetration of a oonpomdfinronghfieolticle usuallyincreasedwifinincreasing lipoginilicityuptoamaxinun, afterwhichfurfierincreasesin lipophilicity reduced fie uptake (Hull, 1970). Conpound wifin a very high partition coefficient in lipid can not be absorbed readily by fie plant (he to high solubility in leaf waxes. They will remain in fie cuticle (Shoe and Wood, 1974; Biggs et al., 1976). Kiri-mood et al. (1982) conpared fie absorption rate of NCPA (4-dnloro-2-nefinylplenoxyaceticacid) and MIPB (4-[4-chloro—2- nefinylphermymityricacid) finrough isolated cuticles. They found that MIPA, a more polar conpound, peretrated more rapidly finan MZPB due to 10 astrongbindingofminfiecuticularuenbree. Bukovac et al. (1971) studied fie effect of chlorination on fie pee’o‘ation of Wtic acid and dicenba (3, 6—dichloro—o-anisic acid) across isolated cuticles of tonato (Lycopersicon eeculentun Mill.) fruits. 'ney found finat increasing fie degree of chlorination of phenoxy acetic acid (POA) enhanced fie trarefer across fie cuticle, wlereas, progressive chlorination of clicamba reduced penetration. The difference in response was apparently due to fie differential effect of chlorination on fie dissociation constant (pK) of fie herbicides. Chlorination of FDA increased lipid solubility wifin little effect on fie pK, wlereas chlorination of dicamba reduced fie pK. Thus, itisapparentfinatanoptimmandsuitablebalancecf polararximn—polargmupinfienoleculeisreededincrderto obtain maximun peetration. 2. Fcrnmlation Ingeeral, several studieshaveshomfinatfieabsorprtioncf rerbicides formlated as esters was greater finan for salts. I-Iauser (1955) conpared fie uptake of 2,4—D (2,4-dichlcrophemiyaceticacid) in several formlations and found that fie ester formulation of 2,4—D was more efficiently absorbed by com (592 gays L.) and soybean (Glycine @_ (L) Merr.) leavesfinanfie amireorfie sodium salts. Similar observation was reported by W (1978). He suggested that the two fornulations of 2,4-D penetrated fie cuticles via different routes. Nbrtonetal. (1968) observedfinattwocrfinreetimesof 2,4,5—T ester was absorbed finan fie amnion salt foruulation. ll 3. Molecular size and might 'Ile effects of radius and weight of a chenical molecule on its diffusion capability finrough fie plant cuticles are not fully understood (Price, 1981). Schonlerr (1978) studied fie uptake of various coupounds wifin different molecular weight and molecular radius and found finat fie uptake was closely related to its mlecular size and weight. I-Icmever, differentresultswerereportedbyRobertsonetal. (1971). They showed finat different subtitnrticns on fie carboxyl group of diphenylaceticacid changed fie corpound absorption characteristic but fie change was not correlated with its molecular weight. B. Adjuvants lngeeral, fieadditionof adjuvantssuchassurfactantsorcrop oil concentrates to fie terbicide spray solutions increases fie foliar absorptionandactivityoffiechenical. Ibwever, arecentstudyby O'Sullivan et al. (1981) indicated finat sone surfactants can antagonize rerbicide activity. AccordingtoCurrierandDybing (1959) andParrandNorman (1964), adjuvants are able to enhance foliar absorption of fie chenicals by pronoting oe or more of fie following: (1) increase leaf wettability and spray retention on plant surfaces by reducing fie surface tension, (2) eliminate fie air films between spray droplets and leaf surface, finus allowing more spray contact, (3) increase fie permeability of leaf cuticles, fa 12 (4) increase fie permeability of fie plasma memrere, (5) acting as hunectant, fierefore, lengthening fie period of peetration, (6) acting as co-solvent, (7) increasirgfiedirectentryfinrunghstonata, (8) facilitate cell wall novement by reducing interfacial tensions. Adjuvantshavebeenreportedtoincreasewettingandretentionof fie spray droplets on fie target leaves (Hull, 1970). Fcy and Smifin (1969) in fieir review suggested that fie surfactant molecules, having entered fie cuticle, may align finenselves in monolayers wifin fieir rm-polarendsorientedinfiecutinandwaxandfiepolarendscould act as hydrophilic layers which would attract water and allows better diffusion of pesticides. Sands and Bactelard (1973) studied the uptake of 14C-piclcran (4-amino-3, 5, 6-trichlcropicolinic acid) wifin various surfactants on eucalyptus (Eucalyptus sp.) leaves. Trey found a positive correlation between l4C-picloram absorption and surfactant effects on leaf wetting. 'Il‘ecretically, anincreaseincontaotareashculdalsoincrease uptakecffiechemicals. However, inprectice, finisfiecryisnot always valid (Price, 1982). Price (1976) studied fine uptake of a . fungicide wifin two surfactants finat had different wetting characteristics. He found fie surfactant wifin lees contact area facilitated greater chenical peetration. Based on his findings, Price (1982) suggested finat fine contact area of a spray droplet may 13 notbeinrportantinpredictingctenicalabsorptionduetofieofier effects of surfactant which may obscure fie wetting effect. A recent SEN study showed finat lipophilic materials in fie spray solutiononleafsnnrfacestendtoconcentrateinanarrowanmlusat fie edge of fie deposits (Baker et al., 1983). Anderson arnd Girling (1983) observed similiar results for surfactants fiey studied. Thus, measurenentofdepositorcontactareawasnotarelevantmefinodin interpreting fie uptake patterns (Anderson annd Girling, 1983). Ingeeral, fiemaxinmnreductioninsurfaceteneionofaliquid cconrs in fie surfactant concentrations range of 0.01% to 0.1%. At higl'er surfactannt concentrations, fie surface tension remains more or less coetant. Mast studies indicated finat enhancenent of rerbicide toxicity by surfactannts takes place at much higner surfactant concentrations finan needed for maxinun wetting (Janeen et al., 1961; Janeen, 1965; Pay and Smifin, 1965). Pay and Smifin (1965) by testing fie efficacy of several snmfactannbsondalaponfomdfinatfieminintunsurfacetensionand contact angles were already reacted at surfactant concentration of 0.1 t00.5%. Butfiemaximnndalaponabsorptionwasobtainedwhenfie concentratioeweretentimeshigner. 'Ihus, assuggestedbyJansen (1964), surfactants at high concentrations may have ofier effects besidereducingfiesurfacetension. (Infiecfierhand, high surfactant concentration can reduce Ierbicide activity by killing fie underlying tissne annd fierefore blocked its own trenslocation (Evans annd Eckert, 1965). Polarity of surfactants have been reported to affect fie e: l4 absorption end activity of herbicides. Hull et a1. (1982) suggested finat fie optimum hydrophilic-lipophilic balence (HLB) value of a surfactantisafunctionoffielerbicide, fietypecfcarr'ier, annd fie plent species. Surfactants most comonly used as spray adjuvants have HLB values between 10 to 13 (mortar, 1986). Snmfactantswifinlcmehavebeenfomdtoenhancefie absorption end activity of DNBP and enitrole (Jensen, 1964). While, surfactantswifinhithLBvalueshavebeennreportedtoenhencefie absorption end activity of paraquat (1,l'-dinnefinyl-4,4'-bipyridiliun) (Evens end E‘ckert, 1965), dalapon (Jensen, 1964), end glyphosate (N- (phosginmeunylglycine) (Wyrill and Burnside, 1977). M optimum HLB value of surfactants for rerbicide penetration may differ for different plant species. Beder end Beder (1964) fcundfinat leavesofsoybeanandcornplentsrequiredsurfactentwifin different HLB values to maximize wetting. Coble et a1. (1970) found anincreasein2,4-Dabsorptionbyhoeyvinemi1kweed[mlems albidus (Nutt.) Britt] using a nonionic surfactent wifin high I-ILB value. hoover, Norris (1973) reported finat 2,4 D peetration finrough fieisolatedpearcuticleswasincreasedonlybyusing surfactent wifin low HLB value. Jensen (1964) in his surfactent efficacy study observed interactions between l'erbicide, surfactant, end plert species. Herbicide formulations may also innfluennced fie efficacy of surfactants. Janeen (1964) observed a chege in fie enrfactant efficacy using different 2,4-D formulations. He reported finat 15 lipophilic surfactants enhannced fie foliar uptake of 2,4-D ester in soybeans but not 2,4-D amine. Kirlmood et al. (1982) sfindied fie peetration of DA and MZPB Ierbicides finrough isolated cuticles end founnd finat snnfactents wifin lovHLBvaluesrechcedpeetretionbutsurfactentswifinhighI-ILB values enhannced peetration. Smith et a1. (1966) reported finat fie number of moles of efinylee oxide (ED) in nncn ionic surfactants was more important in affecting fie toxicity of amitrole, dalapon, end paraquat finan fie nature of fie lipophilic portion of fie surfactant. Severalsmstudieshaveslgwnfinatsoneadjuvantshavefie ability to solubilize or alter fie EN of leaf cuticles (Sends end Bactelard, 1973; Whitehouse et al., 1982; Hart end Price, 1979; Kuzych and Meggitt, 1984). This could allow fie herbicide end fie PM of fine cuticletomixtosoneextent, fiereby, reducingfiewaxbarrierto foliar entry (Mnitehouse et al., 1982). Surfactantsthatarehygroscopicinnaturemayactashmectents byprologing fie dryingperiod of fie spraydroplet annd'finus increasing fie pesticide peetration time (Freed annd Nontgonery, 1958: Holly, 1964). Surfactents have been reported to be able to retain water to more finan 50% fieir weight at high humidity (Price, 1976). Extendingfiedryingperiodoffiespraydropletsonfieleaf surfacebyrewettingfieareaofapplicationhavebeenfomdto inncrease fie uptake of 14C-dalapon (Prasad et al., 1964), end 3—CP (3-chlcro-prqaionic-acid) (Bukcvac, 1965). Tie uptake of surfactents by fie plannts was also influenced by its hygroscopic nnature. Anderson and Girling (1983) measured fie uptake of l4C-surfactants by fie wleat 196 l6 leavesandfcundfinatuptakewasassociatedwifinfiephysical formof fie hydrated snrfactant. According to Miller end St.John (1974) surfactants cen increase fie permability of fie plent nenbrees end finus, facilitating fie peetration of chemical molecules. Norris (1971) proposed finat surfactants applied in concentration above (M: may solubilize fie lipid conpoennts of fie membranes. When fie surfactant concentration in fie solution is above or: level, fie micelles formed could increase fie solulibility of fie compound (Mcthrter, 1986). Mysels (1969) studiedfiecontribnntionofmicellesonfietransportofadyefinrough amembrane. Slefonndthatfiemenbreneactedasabarrierbntfie contribution of fie surfactant was negligible. Several inorganic salts, particularly annmcniun salts, have been usedasadditivestoincreasefieactivityandabscrptionofseveral post-energence rerbicides (Hull et al., 1975). Ann enauple where emnoniunsaltisusedasapartoffieterbicide formllationis lerbicide Amitrole-T, which containns amnoniun finiocyanate (Carter, 1975). Anmmiunsulfateisknmntoenhancefieabscrptionendactiviw of several postemergence l'erbicides such as dalapon (Blair, 1975), picloren (Wilson annd Nishimoto, 1975), bentazon (Suwanketnikon annd Penner, 1978), glyphosate (Turner end loader, 1978), end sefinoxydim (Oncw, 1982). M exact mechanism of fie synergistic action of amnoniun sulfate is still nnot fully understood (Hatzios annd Penner, 1985). Poovaiah end Leopold (1974) proposed finat amoniun salt 17 inncreaseher’oicideabsorptionbyactingonfieplentmembrees. C. Carrier 1. Water Tie majority of rerbicide applications in fie field use water as fie carrier. Factors finat influence fie carrier may also affect fie perfornnence of fie applied chemicals. 'I‘nese factors are water hardness, spray volume, and pH. 'I'nepl-Iofaspreysolutionislcmntoaffectfiedegreeof cuticle peetration sinnce it affects fie degree of dissociation of fie rerbicide noleoules and finus its polarity (Van Overbeek, 1956). Acidic envirornent will also reduce fie dissociation of fie acidic groups in fie cuticle and make fie cuticle less negative (Ven Overbeek, 1956). It is geerally considered finat weak acids will peetrate best at low pH values because fie molecules are undissociated (Hull, 1970). Orgell and Weintraub (1957) reported an, increase in 2,4-D absorption wifin decreasing acidity. Similar observation was reported with dalapon (Pay, 1963)- Bukovacanchrris (1968) fondagreaterbindingofNAA (naphfinaleeaceticacid) infiecuticleatpH3or4finanatpHSor 6. chwever, using NAAm (naphthalene acetamide), fiey found no effect of pH on binding. Buhler and Burnside (1983) tested glyphosate phytotoxicity at different pH levels on oats. They fond increase of phytotoxicity wifin acidic solution but no inncrease was observed at neutral to more alkaline solutions. Water hardness may influence fie activity of sons pesticides due 1 8 to physical or chemical interaction between fie pesticide molecules end fie inorganic ions present in fie solution (Linder, 1972). AccordingtoLinder (1972), hardwateriswaterfinat contains600to 1200 ppnn of CaCIB equivalent and is fierefore alkaline in nabire. In fie Midwest area, moderately hard water contains 120 to 600 ppn of Cacos equivalent. ' Alkalinityoffiehardwatercanreducefieactivityof pesticides if fie solution pH is above fie dissociation constant (pKa) of fie mlecule (Anderson, 1983). Hard water, as fie lerbicide carrier, hasbeenreportedtoreducefieactivityofglyphosate (Buhler end Burnside, 1983; Stahlman and Phillips, 1979; Turner and Loader, 1978). This reduction is apparently due to fie formation of couplex between fie nerbicide molecules end fie polyvalent cations in the water such as (22", Mg”, Fe3”, end A13+ (miner and Loader, 1978). 'Ile influece of spray droplet size on leaf retention and herbicide activity has been extensively studied. Several studies have indicated finat smaller droplet size inncreased fie spray retention end phytoboxicity of post energence nerbicides. McKinley et al. (1972) suggestedfinatfinisincreaseinherbicidal activitywasdueto increase in Ierbicide absorption. Blackman et al. (1958) studied fie effect of droplet size on spray retention by barley (Hordeum vulgare L.) leaves. Trey found finat spray retention increased with smaller droplet size. Similar results were also reported by Lake and Taylor (1974) on wild cat (Avena fatua L.) leaves. l9 Begtsson inn Hull (1970) studied fie spray retention of various droplet sized on leaves with different wetting characteristics. He found finat leaves of hard to wet plants retained more if small droplet sizewasused. W, oneasytowet leaves, fiedropletsizehad nno effect on retention. Tterefore, re suggested finat fie herbicidal enhancement effects of small droplet size were primarily associated with leaf wettability. Smallerdropletsizehasbeenreportedtoincreasefieactivity of several rerbicides, such as 2,4-D (Ennis end Williamson, 1963; McKinley et al., 1972), paraquat (McKinley et al., 1972), fluazifop— butyl (+ )-butY1 2- [4- [ ( 5-(trif1uormlefiiyl )-2-PYridinyl )ODIYJPIWIY] propanncate), sefinoxydim end haloxyfop—mefinyl (2-[4-[[3-chloro-5- (trifltmmefinyl)-2-pyridiny1]mcylplmy]pmpamicacid (Buhler and Burnside, 1984), end glypnosate (Amtecln and Ashford, 1981). Hmever, snall droplet size does nnot always Mass lerbicide phytodcity. Douglas (1968) reported finat fie optinun droplet size to maxindzeparaquatanddiquattoxicitywas400t0500un. Smalleror larger droplets dianeters reduced fie activity of bofin herbicides. Besidefieseadventages, snallspraydrcpletshavebeenrepcrtedto enhence volatilization of 2,4-D-ester (QueHee end Sufierled, 1975). 3. % Oils are also used as carriers for postemergence nerbicide applications. Oils finat are used as rerbicide carriers vary fron, diesel oil and paraffinnic oil, to various oils of plant origin (Hull et al., 1982). M development of new equipnent for low volume 20 Ierbicide application, such as CDA (controlled droplet application), has made it econonically feasible to use oils as a carrier (Bode and Wax, 1984). Accordingtoseveralresearcners (BodeandWax, 1984; Kapustaand Cantwell, 1984; and Kiriumod, 1976), adventages of oil as herbicide carrier are increased retention and peetration of l‘erbicides by fie plent foliage, reduced evaporation of fie spray droplet, end reduce drift. Stonatal absorption can be signnificant in finis situation (Martin end Junniper, 1970). Saunders and Lonnecker (1967) reported finat only about 10% of fie applied oil penetrated fie interoellular spaces of fie leaves. In geeral, fie performance of postemergece herbicides wifin oil asfiecarrieronbroadleafandgrasscontrolinfiefieldhasbeen reportedtobeequalorbetterfinanfiecontrolwifinwaterasfie lerbicide carrier (Qie I-Iee and Sufierland, 1973; Scifres et al., 1973; Bode end Wax, 1984; Kapusta and Centwell, 1984; Barrentine, 1984). III. Plant leaf factors. Severalpropertiesandcharacteristiesofplent leaveshavebeen fond to innfluece fie wetting and absorption behavior of foliar applied chemicals. 'Inese factors are fie leaf onticle, fie leaf age and developnent, fie leaf angle, fie leaf position, fie stcmata, fie trichones end leaf hairs. Each factors will be discussed separately. A. Effects of cuticle. Before penetration finrcugh fie plant cuticle cen occur, spray 21 dropletsoffieapplisdchenicalsmustinpingsandberetainedonfie plent surface (Hull et al., 1982). Tie physico-chemical properties of fie cuticle enrface have been stcwn to innfluence fie wettability end absorption of pesticides. These properties include fie finicknea of fie cuticle, fie chemical conposition of fie article, ed fie orientation ed the physical structure of the wax platelets (Price, 1982; Silva Fernandez, 1965; Holloway, 1970; Hull at al., 1982). Holloway (1970) reported that cuticle finickness, clemical conposition and ultrastructures differed enog fie plent species, fie sens species but different variety, wifin position in fie plant, fie age, andfieenviro'mentinwhichfieplantsaregrown. article waxes are mixtures of log—chain hydrocarboe, alootcls, ketones, fatty acids, esters, and aldehydes (Hull at al., 1982; Holloway, 1970). In geeral, waxes wifin significant quentity of log-chain ketoes end alkees were fie most diffianlt to wet regardless of fie article finickness (Juniper, 1960; Silva Fernandez, 1965; Junniper end Bradley, 1958; Holloway, 1970). 'Ile relatively non-repellent waxes consist largely of diols, sterols, end triterpecids (Holloway, 1970). Tie retention of herbicide spray droplets are also influeced by fieginysical strucfilreedorientationoffiewax. Several researchersobservedfinatsnoofinsurfacesweresasisrtowetfinan rough surfaces (Bayer and Lunb, 1979). Junniper (1960) also reported a strog water repsllency on leaves wifin crystaler or semi- irregular waxes. Cuticle finickness varies widely depeding on fie plant species 22 and fie environmental coditions. Martin and Junniper (1970) studied leaf article finickness of various plant species and observed finick- nessfinatvariedfronOJuninoeplantspeciesto13.5umon ecfierspecies. Tleamountofwaxproducedbyplantisalso influenced by light, tenperature, and relative humidity (Hull, 1970). Tribe et al. (1968) reported finat fie quality of wax produced in cat ed barley leaves was directly proportional to light intensity but innversely proportional to fie relative humidity. Tte finickness of plant article does nnot always related to chemical absorption rate. Sons studies indicated finat increase in lerbicids absorption is related to decrease cuticle finickness (W, 1973; Pereira et al., 1971); wlnils ofiers failed to show fie correlation (Norris, 1974; Price, 1982; Al-Jaff at al., 1982; Cook et al., 1979). Norris (1974) reported finat article permeability to 2,4-D penetration was more closely related to fine conposition of fie wax and article rafier finan fie cuticle finickness. Thus, as Price (1982) mentioedinhisrevisw, fiestructureedfiechenical coupositionof plant articles vary so much between species finat fiess two factors will override fie effect of finickness aloe. Tlewaxdistributiononfielsafsurfacsgeerallyisnct unnifcrm. Kravkina (1972) observed areas on quackgress leaves that had fininnnerornnowaxdeposits, suchasfiecentralportionabovefie vsinns, fie leaf marginns, fie area above anticlinnal cell walls, fie centerpartoffieguardcells, andonfielsafhains.Theseareahave attn 1965 Dead 3111“. plam 1952). 23 been reported previously as fie preferential sites of uptake of foliar applied chenicals (Yenada et al., 1966; Franks, 1967). B. Effects of leaf age end developnent Tneageedderelopnentalstageofaplantleafhavsbsensrcm to innfluece fie absorption of several pesticides. This is partially attributedtofiednegeinmorptclogy, conpositionandannountofwax presents on fie leaf surface wnen fiey get older (Davis, 1971). In geeral, young actively growing leaves will absorbed greater announnt of foliage—applied chemicals finan more mature leaves (Bukcvac, 1965; Kirkwccd at al., 1972; Sargent and Blackman, 1972; King and Radosevich, 1979). Thisisoftenaccreditedtofiefininnnerendmore permeable anticlss found on yonnger leaves (Leon and Bukovac, 1978; Price, 1982; King ed Radosevich, 1979). Bukcwac at al. (1979) observed a decrease in NAA (l-Naphfinylaceticacid) absorption by fie peach (Prunnus persica L.) leaves during fine developnent. They also attributedfiechangsinanticlepermeabilitytofiechegsinfiewax conposition. Sifton (1963) observed finat articles of several young plent species were not fully developed. C. Effects of leaf egg Retention of spray droplets is also a function of leaf egle (Hull at al., 1982). leaves of nonocotyledons plannts are nearly verticalwhsnnyonngandbeconemorencrizontalasfieyelogatsed expend. Allofierfacborsbeingsqual, lsafwifinnorehcrizontal orientation will intercept greater spray solution (Ennnnis et al., 1952). 24 D. Effects of adaxial vs abaxial leaf surface and fie role of stonata Severalstudieshaveslcnmfinatfieerountofchenicalsabsorbed byfieadaxialorfieabaxial lsafsurfacesarennotidenntical. This is often attributed to fie differecs in anticls finickness, conposition, and fie number of stonata present (Price, 1982; King and Ranbsevich, 1979; Al-Jaff et al., 1982). King and Radossvich (1979) reported fie abaxial leaf sm‘facs of tecak (Lificcarpus densiflorus L.) have fininrer articles and absorbednorslerbicidesfinanfieadaxial leaf surface. Hcmever, anticls finickness is not always fie determining factor in pesticide absorption. Basicuny and Biggs (1976), Bukovac at al. (1979), ed Al-Jaff at al. (1982) reported finat a finicker article on oe surface cenbenrorepermeabletoapartianlarsolutsfinanafininneranticlson fie ofier surface. Price (1982) also observed finat fie adaxial end abaxial leaf surfaces may show preferential permeability to different corpcunnds regardless of fieir cuticle finickness. Hunt and Baker (1982) using leaves of 12 different plent species also fonnd finat fie uptaksofNAAbyfineadaxialorabaxial leafsurfacescennotbe attributed to fie mount of wax deposit aloe. Several worker have speculated finat differential in chenical psrmeabilitybetweenfieadaxial andabaxial lsafsurfacesisdnsto fiehignernunbersofstonatapresentinfieabaxial surface (Freibsrg and Payne, 1957; Sands and Bactelard, 1973). Uptake studies wifin flncrescecedyesedradioactivererbicidshaveslmfinatuptaksby stonatacolldocanrifsurfactentswereaddedtofiespraysolution 25 (Clnrrier end Dybing, 1959; Currier et al., 1964; Prasad st al., 1962). However, Sargent (1965) observed no direct penetration of several growthregulatorsintofieopenstonata. Healsoroticedfinatfie gronfin regulators entered fie guard cells and fie enticlinical walls offieaccsssoryandepidermal cells. Ofierabsorptionstudiesby ssveralressarctersalsoreportedfiesameobservations, whichis, chenicals peetrated fie guard cells and fie accessory cells innstsad of stonata pores directly (Sargent end Blackman, 1962; Dybing and Currier, 1961). Schonterr and Bukovac (1972), who studied fie infiltration of aperturewall egles, snggestedfinatfiedegreeofsbonataopeningis nctinnportentinfieabsorptionprocsssofaqueansspraysolutiondne tofiephysical constraintimposedbyfiestonatal chanbers. W, specializedrmtesassociatedwifinguardandaccessorycellsmay account forfiedifferecsinchenicaluptaksbstweenadaxialed abaxial leaf surfaces. Stonata are Host frequently or if not exclusively located on fie abaxial side of fie leaves (Hull at al., 1982). Apparently, stonetal penetration requires a spray solvent wifin averylozsurfacstensionandgoodwettingcharacteristics (Craft, 1964). I-bnever, volatile lerbicides cen enter fie plent leaves finrough open stonata by gas diffusion (Hull, 1970). D. Effects of trichones and leaf hairs T‘nein'portanceofchenical absorptionviatrichonesandleaf hairshasbeenenphasizedbyflull (1970). T‘richomesmayinnfluece wetting and dispersing characteristics of spray droplets on fie leaf 26 surface ed provide a site of entry of foliar applied chemicals. Wettabilityisinfluecsdbyfiesize, fietypeedfiedensity of trichones on fie leaf surface (Hull et al., 1982). A finick netting of tricrcnes may make fie foliage difficult to wet. Ennviromental coditions were reported to influence trichnme develcpnnent (Sharma, 1972). Clnallen (1962) studied fie effects of fi‘ichone patterns on leaf wetting. Hefonndfinatfie "open" patternsenhancedwettingdueto capillary action, while fie "close" patternns have a water repellent surface. Droplets fron foliar spray may shatter upon impact wifin fine trichones. Hess at al. (1974) found finat fie degree of shattering edfieannountofdroplstsreachingfielsafsurfacsweredepedenton fie spray volune and fie droplet size. At higler spray volune, fie droplets shattered into numerous enaller droplets upon inpact wifin fie trichones, but sole droplets reacted fie surface. I-Icwever, at low sprayvolune, fiedroplstdidnotbreakuponimpactbutattactedto fietrichonesandveryfswreachfiesurface. Studies wifin fluorescence dyes indicated finat trichones are possible site of entry for foliar applied chemicals. Benzing ed Burt (1970) studied fie uptake of cations on twenty plant species end found greateruptaksocalredonleavescoveredwifintrichones. Bukovac (1970) observed finat fie silver fron a silver nitrate solution acamulatsd in fie trichones, especially trichones finat were located over fie veins. Similiar observation using flncrescent dyes were also reported by Hull (1967). Since fie basal cells of trichones on fie 27 leaf surface have little or no anticls at all (Bull, 1970), finese cells are fie principal site of uptake of aqueous solution (Linsken et al., 1965). IV. Ehviro'mentalfactors Severalenviro'nentalfactorshavebeenreportsdtoinfluecsfie absorption and tranclocation of foliar-applied chemicals. Tress factors such as light, temperature, relative hunidity, soil noisture, and rain will be discussed separately. A. Effects of ligt Tne effects of light on pesticide absorption generally are diffianlt to elucidate due to fie difficulty in adjusting light intensity or quality wifinout affecting fie teuperature end hunidity of fie microenviro'ment (Hull, 1970). T're influence of light on lerbicids absorption by plents foliage cen be direct or indirect (Muzik, 1976). Light is known to affect several physiological processes in plants such as photosynfiesis, transpiration, end stonatal aperture. Currier and Dybing (1959) suggestedfinat lightincreasedfieabsorptionofherbicidestyopening fiestonataoffieplantandfinus, allowingnnoreenfiyroubesforfie chenicals. Schuster (1971) reported finat night applications of phecxyherbicidesondessrtplents, whichopenfieirstonata at night, was none effective finan daytime application. However, since lerbicids peetration via fie stonata is very limited, ofier factors such as fie synfiesis of photoassimilats necessary for lerbicids treeport may also explain fiess effects. leaf 1972 J inter of ep (Will influ 1976) 1975). 28 Expoenre of plents to high light inntensity were found to increase leaf wax production (Tribe at al., 1968; Whitscross and Armstrong, 1972). Whitscross and Armstrog (1972) observed finat low light intensity altered fie wax structure fie plants. Chenical conpositions ofepicutianlarwaxisalsoreportedtobeinfluecedbyphoboperiod (Williamson, 1972). Tiess indirect effects of light will definitely influence fie absorption rate of foliar applied lerbicides (Muzik, 1976). Ingeeral, fiedirecteffectof lighthasbeenreportedto enhance herbicide absorption (Robertson et al., 1969; Hull at al., 1975). Sargent end Blackman (1965) measured peetration rats of 2,4—D unnder different light intensities and observed increased 2,4-D absorption as light intensity was increased. Glypl‘csats activity was also increased wifin increasing light intensity (Ann-Irmaileh end Jordann, 1978). Shading decreased fie trenslocation of l4C-fluazif0p -buty1 in quackgrass (Kells st al., 1984). B. Effects of air temperature and relative humidity Air tenperature and relative hunidity (RH) directly influece herbicide absorption and translocation in fie plents. In geeral, the uptake end trannslocation of nost postemergece lerbicides increased wifin increasing temperature and runnidity. Wills (1984) reported that fie absorption of l4C—ssficxydim by bermudagrass (ggcdon dactylon) (L.)Psrs.)1eaves, after 2 days, was 70%at35Cand100%RH, 56%at35Card40%RI-land32%to43%at18c and 40% and 100% RH. Tie trannslocation of ssfincxydim was also greater at big et a1 . aciflu fluazi 29 at higher temperature and at higher relative humidity. Increasing fie air temperature and fie relative humidity was also reportedtoincreasefieuptakeandtranslocationof dalapon (Prasad et al., 1967); glyptesate (Wetter et al., 1980; Jordan, 1977); acifluorfen (Wills and McWhor'ter, 1981); bentazon (Wills, 1976); fluazifop-butyl (Kells, et al., 1984); and haloxyfop—nefinyl ( Harrison and Wax, 1986). Hovever‘, when fie relative hunidity is at maximn (100%), irncxeasingfietanperaturemaynotchangefiealomtof lerbicids translocated (Jordan, 1977). Van Overbeek (1956) suggested finat temperature may influenced fine diffilsionrateofoorpomdsfinrolghfiemenbrarebyreducingits viscosity. Eckl and Gruler (1980) found phase changes in cuticles finatwereecposedtodifferenttenperamreregines. 'Itesechanges decrease cuticle visoocity (Price, 1982). Temperature indirectly affect fie absorption of rer‘bicides by regulating fie quality and quantity of fie wax formation in plant leaves. Increaseintenperafilregeerallyreelltedinnmewaxbeing produced (Hull et al., 1975). Whitecross and W (1972) also reticedadnengeinwaxultrastructurewhenplantsweresubjectedto different temperatme systems. Relative hunidity enhances fie absorption and translocation of terbicides in plants by prolonging fie drying of fie spray droplets on fie leaf surface, increasing fie cuticle hydration (Prasad et al., 1967; Mlzik, 1976; Hull, 1970), and to a enaller extent favor stonatal opening (Hull, 1970). 30 C. Effects of rainfall Rainfall will renove fie lerbicide deposits fron fie plant leaves dependingonfiequantityoffierain, fietineelapsedbefiweenfie lerbicide application and fie rain, and fie lerbicids solubility (Hull, 1970; Mlzik, 1974). 'n'e activity of fie herbicide will be reduced if rain falls soon after application, particularly wifin lerbicides finat peetrate slowly such as dalapon (Mlzik, 1974) or water soluble lerbicides, such as paraquat (Bovey and Diaz-Oolon, 1969). Lipophilic l'er‘bicides are less susceptible to removal by rainfall finan water soluble rerbicides (Bovey and Diaz-Oolon, 1969; Behrens and Elakkad, 1981). Liinsoorttandnagin(l968) reportedfinatincreasingfieanomtof sinulated rainfall applied to several forage crops resulted in increased 2, 4-D loss fron fie foliage. Application of simulated rainfall imnediately after postemergence herbicide applications reduced fie activity of 2,4-D (Behrens and Elakkad, 1981), desnedipham end phemedipham (Anderson and Arnold, 1985), and bentazon (Doran and Anderson, 1975). Addition of gray adjuvants was reported to reduce fie detrimental effects of rainfall (Doran and Andersen, 1975). D. Effects of soil moisture Aprolongedperiodofsoilmoisturestresshasbeenfoundto induce fie developnent of finicker cuticle on several plant species (Baker arnd Prooopiou, 1980). 'I're increase in wax deposition may affect fie absorption and activity of foliar applied terbicides. Moosavi-nia and Dore (1974) found finat glyphcsate phybotoxicity Instr oft 31 onseveralgrassspecieswasreducedmderextrennemisturestrees. However, returning fie stressed plants to field capacity oe week before lerbicids treatment did nnot reduce fie glyphcsate activity. Hunt and Baker (1982) nnoted finat decreasing fie soil moisture content increasefiewaxproductioninpea (PisunsativunL.) leavesand decreased fine peetration of NAA. According to Hull (1970), nnoisture stress reduced fie translocation of foliar-applied herbicides. Hovever, its influence on lerbicids absorption is still unclear. Several studies have shown finatwaterstressreducedfieabscrpticnandtranslocationofseveral nerbicides including 2,4-D (Hauser, 1955; Davis et al., 1968), piclcran (Davis et al., 1968), bentazon (Wills, 1977), and glynincsate (Atmadi et al., 1980). Ibwever, ofier studies also indicated finat misturestressdidnnotaffectfieabscrptionofcfierl'erbicides, such as 2,4-D (Basler et al., 1961), picloram (Merkle and Davis, 1967; Lauridson et al., 1983), dicanba (Lauridson et al., 1983); diclofop— nefinyl (Dortenzio and Norris, 1980; Akey and Harrison, 1983), and fluaaifop-mtyl (Kells et al., 1984). Evenfinough fie absorption offinesererbicidesbyfiesoessedplantsweremtaffected, fie lerbicidal activity of fieee chemicals was severely reduced. Apparently, fie absorption of terbicides by plants under moisture stressmaybeinfluencedbyfiedurationof stress, fieplant species, and fie lerbicids. The literatures indicated that chenical absorption by fie plant leavesisaveryconplexprocess. 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K’JRQ 549.50 R59 121 . 122 . 123. 124 . 125 . 126 . 127 . 128. 129 . 130. 131 . 132 . 43 Sargent, J. A. and G. E. Blackman. 1965. Studies of foliar peetration. II: 'I‘re role of light in determining fie peetration of 2,4 dichloro pheexy acetic acid. J. Exp. Bot. 16: 24-47. Sargent, J. A. and G. E. Blackmann. 1972. Studies of foliar peetration. 1x. Patterns of peetration of 2, 4 dichloro- ;ineexyacetic acid innto leaves of different species. J. Exp. Bot. 23: 830-841. Saunders, P. F., C. F. Jenner, and J. E. Blackmann. 1966. Tre uptakeofgrowfinsubstannces. VI. Aconparativestudyoffie factorsdeterminingfiepatternsofuptakeofpheexyacetic acid and 2,4,5-trichloropheexy acetic acid, weak and strong auxinns, by Gossypiun tissues. J. Exp. Bot. 17:241. Saunders, R. K. and W. M. Ionnecker. 1967. Physiological aspects of using nnon phytotoxic oils with herbicides. Proc. North Centr. Weed Oontr. Conf. 21: 62-63. Schonlerr, J. and M. J. Bukovac. 1972. Peetration of stonata by liquids. 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S. 1965. Studies on plannt cuticle. VIII. Surface waxes in relation to water repellency. Annnn. Appl. Biol. 56: 297-304. 133. 135. 136. 137. 138. 139. 140. 141 . 142. 143. 144. 133. 134. 135 . 136 . 137 . 138 . 139 . 140. 141 . 142. 143. 144. 145 . 44 Snnifin, L. W., C. L. Foy and D. E. Bayer. 1966. Structure- activity relationship of alkylpheel efinylee oxide efier non-ionic surfactants and finree water soluble Ierbicides. Weed Res. 6: 233. Stahlman, P. W. and W. M. Phillips. 1979. Effects of water quality and spray volune on glyplesate phytotoxicity. Weed Sci. 27: 38-41. Suwannketnnikon, R. and D. Penner. 1977. Additives to increase bentazon and glyptesate activity for yellow nutsedge ( esculentus L.) control. Abs. Weed Sci. Soc. Amer. p 91-92. Tribe, I. S., J. K. Gaunt, and D. W. Perry. 1968. Ontiollar lipids in fie Grannineae. Biochem. J. 109: 8-9. Turner, D. J. and M. P. C. loader. 1978. Oonplexing agents as herbicide additives. Weed Res. 18: 199-207. Van Overbeek, J. 1956. Absorption and translocation of plant regulators. Annu. Rev. Plant Physiol. 7: 355-372. Whitscross, M. I. and D. J. Armstrog. 1972. Ennviromenntal effects on epicuticular waxes of Brassica nag L. Aust. J. Bot. 20: 87-95. Whitehcuse, P. and P. J. Holloway, and J. C. Caseley. 1982. 'He epicuticular wax of wild cats in relation to foliar entry of fie lerbicides diclofop-metyl and difenzoquat. In The Plant Onticle, D. F. Cutler, K. L. Alvin, and C. E. Price, eds. Linnnn. Soc. Sym. Ser. 10. Academic Press, London. p. 315-330 Willieneon, R. E. 1972. Sicklepod hydrocarbon response to pletoperiod. Phytochenn. 11: 1273-1280. Wills, G. D. and C. G. Werter. 1981. Effect of enviroment on fie translocation and toxicity of acifllerfen to showy crotalaria (Crotalaria spectabilis L.). Weed Sci. 29: 397-401. Wilson, B. J. and R. K. Nishinnoto. 1975. Anmonium sulfate enhaneenennt of piclcram activity and absorption. Weed Sci. 23: 289-296. Wyrill, III, J. B. and O. C. Burnside. 1977. Glyptesate toricitytocomonmilloweedanndhsmpdogbaneasinfluencedby surfactant. Weed Sci 25: 275-287. Yamada, Y., H. P. Rasmussen, M. J. Bukovac, and S. H. Wittwer. 1966. Binding sites for inerganic ions and urea on isolated cuticular menbrane surfaces. Amer. J. Bot. 53: 170-172. 146. Ya 45 146. Yamada, Y., S. H. Wittwer, and M. J. Bukovac. 1964. Peetration of ions finrough isolated cuticles . Plant Physiol . 39: 28-32. IDE CHAPTER 2 IDENTIFICFXTICN OF SUPERIOR ADJUVANTS FUR SEI'I-DXYDIM AND BENTAZON ABSTRACT Various experimental adj uvants were tested to maximize herbicidal activity of sefieunydim {2[1-(efiexyimine)butyl]-5-{2-(efinylfinio) propy1]-3-hydroxy-2-cyclotexen-l-oe} on quackgrass [Agropyron repens (L.) Beauv #1 AGRRE] and bentazon [3-isopropyl-lH-2,l,3- benzofiniadiazin—4(3H)—oe 2,2-dioxide] on cannon lannbsquarter (Oenepodium album L. # CHEAL). Identification of superior adjuvants were doe by nneasuring fie 14C-terbicide droplet spread and absorption, as innfluenced by various adjuvants, on fie target weed. Tte absorption and droplet spreadability of sefiexydim and bentazononquackgrassandlambsquarter leaveswasinncreasedor decreaseddepedingonfietypeof adjuvantused. Apocrcorrelation was fonndbetweensefiexydimdropletspreadandabsorptionon quackgrass. With bentazon, fie relationship between finese two factors was greater. 'I‘hus, neasurement of droplet spread, as affected by adjuvants, was useful only as a screening technique for bentazon. Blending surfactants with paraffinnic oil or soybean oil to form a lLetters following finis symbol are a WSSA-approved connputer code fron Oonposite List of Weeds, Weed Sci. 32, Suppl. 2. Available fron WSSA, 309 West Clark Street, Champaign, IL 61820. 46 (leper ident surf 61 47 crop oil concentrate changed fie efficacy of fie surfactant conpared to fie surfactant by itself. Surfactants nest effective as conpoents of paraffinic oil based crop oil coeentrate were different finan surfactants ideal for inclusion with soybean oil based crop oil coeentrate. Thus, fie effectiveess of a crop oil concentrate depeds on herbicide, surfactant, and oil types. In fie field, several of fie superior adjuvants, which were identified in fie laboratory, enhaneed sefiennydim annd bentazon activityongrassandbroadleafweeds. Tteinteractionbetween surfactant and oil types on fie adjuvant efficacy was also apparent. 48 INI'RCDUCI'ICN Adjuvants are materials finat enhanee action of fie lerbicids or nedify characteristics of fie lerbicids fornmnlation or spray solution. Adjuvants are frequently added to postenergence lerbicids spray solutions to enhanee lerbicids activity. Adjuvants with finis function are classified as activator adjuvannts. Tress consist of surfactants and oils (McWIerter, 1986). According to Parr and Norman (1965) and Holly (1964), adjuvants enhanee lerbicids peetration and effectiveness of foliar applied terbicidss by lowering fie liquid surface tension, improving spray coverageandinncreasingdropletspreadontarget leaf, actingasa co-solvent or hunectant, and increasing plannt membrane pernneability. hrrfierresearchonadjuvantactionhassrownfinatitmaydisruptfie epicuticular wax (Whitehcuse et.al., 1982; Sands and Badelard, 1973). Hydropnilic-lipqinilic balanee (HLB) value of an adjuvant has been related to lerbicids retention in fie cuticle annd herbicide absorption (Kirkwood et al., 1982). Before 1974, fie major activator adjuvants included inn postenergeee lerbicids application were mostly surfactannts . Sines finat time, surfactant-petroleunn oil blends, conmonly called crop oil concentrates (CDC), have beccne popular as spray adjuvants (Mcwnerter, 1982). Recently,fierehasbeenintsrestinfieuseofsoybeanoilasa repli in u: for a (Nale appll' sefie 49 repth for petroleunn oil in cr0p oil coeentrate. 'Ite advanntages in using soybean oil in lerbicids adjuvannts ineluds creating a market foranagriculturalproductandtelpingtoconservepetroleunoil (Nalewaja and Skrzypczak, 1986). Sefincanydim, a nnew postenergeee grass lerbicids, is usually applied in connbinnation with an adjuvant. In geeral, fie addition of acropoil concentratetofiesefiexydimspraysolutionincreased ssfiexydim phytotoxicity on grasses (Buhler and Burnside, 1984; Hartzler and Pay, 1983). Research data indicated finat soybean oil coeentrate (SOC) could be equally effective as petroleun oil coeentrate (POC) in enhancing sefinoxydinn activity (Harrison and Wax, 1983; Chaney annd Kapusta, 1984; Kells annd Wannannarta, 1986). Unfortunately, net all adjuvants are appropriate and effective for all lerbicides. O'Sullivan et al. (1982) tested 14 different surfactants for glypl'esate (N-ptesphononefinylglycine) and fonnnd that six surfactannts reduced glyptesate phytotcxicity. Petersen et al. (1985) also observed finat not all of fie seven surfactants tested increased 14c-dicanba (3,6-dichloro-o—anisic acid) absorption by soybeann. Nalewaja at al. (1985), tested several enmlsifiers for effectiveess in crop oil coeentrates. Efficacy depended on fie lerbicids, fie specific ennulsifier, annd fie peroent of emlsifier present. 'Iterefore, screening and identifying fie appropriate surfactant foreachindividualrerbicideusageisveryimportantand useful. Penner et a1. (1984) developed several technniques to screen SO surfactants. Treyscreeedannunberofexperimentalsurfactantsby neasuringfiedropletspreadonaglasssurfacs,waxpaper, water sensitive andoil sensitive papers, andquackgrass leaves. Assnning finat large droplet spread is associated wifin greater snrfactant action,fieyfoundfinatfiespreadcharacteristicofasurfactanrt changedwifinfiespecificsurfaceusedinfietest. Thus,screening techniquesondifferentsurfacssofierfinanfietargetweedleaves, hadaverylinnnitedvalue. Tleobjectivesoffinisresearchweretodevelopavalidtestfor rapidlyidentifyingdesirablesprayadjuvantsandtousefietest systenn to identify adjuvants finat increase sefinonnydim and bentazon absorption and efficacy. plas high with 90811;): Water “@831. Ofa Q 51 mmrznnsmmnnsmms Generalprocsdures. Quackgrassrhizonsssctionswifintwoor finneenedesorlannbsquarterseedswereplacedian-ondioneter plasticpotscontaininggreenhousepottingsoilandwerewatered daily. Fertilizerwasappliedoeeaweektomaintainoptinmmgrowfin. Planntsweregrowninagreenhonsewifinenpplemental ligh‘tingfron high pressure sodium lights. 'ne light intensity was 500 US nu’2 s"1 wifin only supplemental lights to 1200 uE m'2 s"1 with bofin supplemental light and natural sunnlight. Tte greenhouse was maintained at 27 C, 40 to 75% relative hunidity (RH) and 16 h daylength- Quadngrassplantswere8to9weeksold, 20to30cmtalland lelmeere4m5veesoldedmmw1Wmusedfm terbicide absorption studies. Absorptionstudy. Instndiesneasuringfieabscrptionof l4C-ssfiexydim by quackgrass, 14C-ssfiexydim labeled at fie #4 position in fie ring (spec. act. 13.063 mCi/mnel) was added to conmercially fornnulated ssfiexydim, distilled water, and adjuvants. Sefiexydinnn was applied at a rate equivalent to 0.56 kg/ha inn a water carrier of 187 L/ha. 'Iwo microliter of 14C-sefiexydim solution wasappliedwifinamicrosyringetofiecenteroffieadaxial surface of a quackgrass leaf. Radioactivity applied to each plannt was 0.01 uCi. 2.4 with 00114 solut reppe reply data] Water 52 To exanine fie effect of experimental adjuvants, adjuvants were added to fie sefiexydinn spray solution at 1.2 L/ha for surfactant and 2.4 L/ha for paraffinic oil (POC) or soybean oil (SOC) concentrates. FCC and soc were formulated by mixing paraffinic oil2 or soybeann oil3 withfiesurfactantsataratioof4to1. Treatedplantswereplacsdinagreenl'eusewifinconditionsas previously described for 10 h. After 10 h, fie treated leaves were rinnssdwifin 10ml acetoe fronapipetteandfieacstoewashwas collected in a scintillation vial. Tre acetoe was finen evaporated to drynessatroonteuperature for48hand12mlof scintillation solution was added. Radioassay was done by liquid scintillation spectronstry. 'I'reamountofradioactivityinfieacstoewash representedfiererbicidsfinatwasnetabsorbedbyfieplants. All necessary ccrrectioe for background were done. 'Iteexpsrimental designusedwasconplstelyrandonizedwifinfinree replications per treabnnent. All experiments were repeated and fie datarepcrtedarefieueansoftmexperinnents. Infiestudymsasuringfieabsorptionof 14C-bentazonby lenbsquar‘ter, 14C-bentazon labeled unniformly on fie phenyl ring (spec. act. 13.7 mCi/mnel) was added to comercially fornnulated bentazon, distilled water, and adjuvant. Bentazon was applied at a rate equivalent to 0.84 kg/ha in a water carrier of 187 L/ha. Two microliter of 14C-bentazon solution 2SlnnSpray 11 N, aproductof SunnRefiningandMarketing Co. 3Fully refined soybean oil. mmmm m lan m m m adj] Wate 53 was applied wifin a microsyringe to fie adaxial surface of lannbsquarter leaf. Radioactivity applied to each plant was 0.01 uCi. To examine fie effect of experinnental adjuvants, adjuvents were fornmnlatedandaddedtofiebentazonspraysolutionwifinfiesane nefiedsandratesasinfiessfiexydinnstudy. Treatedplantswere placed in a greenreuss wifin coditions as previonsly described for 72 h. After72h, fietreatedleaveswererinsedwifin lOmlof acetoe. Tteradioassayprocedureswereidenticaltofieprocedurein ssfincxydim study. Droplet spreadabilig study. Two microliters of sefiexydim or bentazon solutions, prepared as previously described, were applied to fieadaxial surfaceofquackgrassorlanbsquarterleaves, respectively. After fie droplet dried out, fie dianeter of fie leaf spotwasnneasnredwifinacaliperandrecorded. Adjuvant efficacy. Agreenhoussstudywascoductedtoexamine fie effect of selected experinnental adjuvants on bentazon control of lennbsquarter. Lenbsquarterplanntsweregrowninagreenhousewifincoditionsas previonslydescribed. Lenbsquar‘terplants atStoBonninleightwere treated in a enraying chamber wifin bentazon at 0.11 kg/ha, 0.28 kg/ha, end 0.56 kg/ha, respectively. 'I're various surfactents, POC, end SOC adjuvants were applied at 1.2 L/ha, 2.4 L/ha, end 2.4 L/ha, respectively. Tie lerbicids spray solution was applied in 187 L/ha water at 207 KPa pressure using Tee Jet4 8001B nozzle. 4'8an System 00., Wteaton, Ill. 54 Plent injury was rated 10 days after treatment on a 0 (re effect) to 100 (couplets kill) scale. Fresh weight determination was doe by harvesting fie plants. Each treabnennt was replicated four times. Field sttdies were coducted in 1984 and 1985 in East Lansing, M1 to examine fie effect of a few selected experimental adjuvants on Iquackgrasscontrol wifinssfiexydimanndonbroadleafweedcontrolwifin bentazon in soybsen. 'Ocrsoy79' soybeenswereplantedin76cmwiderowsandfieplot sizewas3mby9.lm. A11 herbicidsapllicationsweremadeusinga tractornonnntedcoupressedairsprayertravelingat4km/hand delivering a spray pressure of 345 KPa. 'nequackgrasscontrolstudyinl985wasacconplisledusing'ree Jet 730154 and 730077 nozzles, which delivered 140 L/ha and 70 L/ha, respectively. For fie broadleaf weed control study in 1984 and 1985, Tee Jet 730308 nezzles, which delivered 280 L/ha, were used. Sefien-nydim was applied at 0.56 kg/ha, while bentazon was applied at 0.84kg/ha. Surfactent, POC, andSOCwereaddedtofiessfiexydim or bentazon spray solution at 1.2 L/ha, 2.4 L/ha, and 2.4 L/ha, respectively, regardless of fie spray volunes. Ttequackgrasswasatfiefinrestofourleafstageatfietinneof sefiexydim application. Oomon ragweed and redroot pigweed were at fiefonrtosixleafstagewnenfiebentazontreabnentwasapplied. All studies were designed as a randonized couplets block wifin finree replications . Visual evaluations of quackgrass control were taken4weeksafterapplicationandatsoybeanharvest. Forfie broadleafweedcontrol study, visualsvaluationsweretakenlOand35 55 days after treatment. Weed control was visually evaluated on a scale of 0 (re effect) to 10 (couplets kill) scale and converted to percent weed control. 56 RESULTS AND DISCUSSICN Sefinoxydim spray droplets fron a spray solution designed to deliver 0.56 kg/ha of sefiexydim in a spray volune of 187 L/ha had a maxinnmnspreadofSnnmonquackgrass leaf (AppedixTable l). For190 experimental surfactants tested for innclusion in fie spray solution, spray droplet dianneter varied fron 4 nun to 49 um (Appendix Table 1-4). Alfinongh greater spray droplet spreadability increased fie total leafareaincontactwifinfiespraysolutionandspraydroplet spreadability is readily neasured, finis parameter is relatively neeninglessunless it alsoresultsingreaterrerbicideabsorptioned action. Tteabsorptionof14C-sefiexydimbyquackgrassleavssinfietsst systemwas 17%offieappliedinfieabsenceofenadjuvannt (Appendix Table 1). Inclusion of the crop oil ooeentrate, Herbimaxs, at fie reconneded rats of 2.4 L/ha inncreased l4C-sefiexydim absorption to 40% of finat applied (Appendix Table 3). Experimental adjuvants testsdresultedinl4C-sefiexydimabsorptionrangingfron6to77%of finat applied (Appedix Table 1-4). 'I'te best adjuvant was a fatty acid mixture surfactant, D76 (Appedix Table l). 5HerbimaxisaconnnnsrcielproductofUnnionCarbideOo. 6B0i181500,alsoaconnpoenntofDASH,productofBASFChemical Oonpanny. 57 Tie results provided little semblance of a relationship between spray droplet spreadability and 14C-ssfiexydim absorption by quackgrass leaves (Figure 1). This is consistent wifin previousrepor‘ts by Price (1982) for fie absorption of efinirinnel (5-butyl-2—efinyl amine-4-hydroxy—6-msfinyl-pyrinnidine) by wrest (Triticum aestivun L.) leaves. Tre lack of an observed relationship between spray droplet spreadability and 14C-rerbicide absorption strogly indicates finat fie use of 14C-herbicide absorption as a criteria for evaluating adjuvants is superior to evaluation of spray droplet spreadability, at least for ssfiexydim on quackgrass. Flnrfiernnere, fieresults indicatedacritical funnctionofierfinan fie reduction of surface teeion as a key role for fie adjuvants. Ofier funnctions proposed inncluds fie ability of fie adjuvant to solubilize fie leaf cuticle (Sands end Bactelard, 1973; Whitereuss et al., 1982), influees of fie adjuvant on fie physical properties of fie lerbicids (Kirkwood et al., 1982), hunectant properties of fie adjuvent (Holly, 1964), end adjuvant effects on plannt mennbrees (Miller end St. John, 1974). Tie results of finis study also illustrated finat sone adjuvannts were less effective finen ne adjuvant with respect to 14C-sefinoxydim absorption by quackgrass leaves (Appedix Table 1-4). O'Sullivan evaluated adjuvannts for glyplesate (N-pl'esphononefinylglycine) and arrived at a similiar coelusion. Similiarly Petersen et a1. (1986) noted finat net all surfactants fiey tested were effective for dicamba (3, 6-dichloro-o-enisic acid). 58 Bleding a surfactant with paraffinnic oil or soybean oil, to fornmllate POC or SOC, resulted in adjuvant efficacy unpredictable from fie efficacy of fie surfactant evaluated by itself. Thus, surfactants giving fie higlest sefiexydim absorption rate by quackgrass leaves were net identical to surfactents nest effective as conponents of SOC or POC (Appedix Table 1-3). Slmfactants ideal for inclusion wifin soybeann oil were also different finen surfactants ideal for use wifin paraffinic oil to form crop oil concentrate (Appedix Table 1-3). TIere appeared to be an interaction between surfactant and oil types on fie ability of an adjuvent to facilitate 14C-ssfiennydim absorption. Nalewaja et al. (1985) conpared several emulsifiers as conponents of CDC end fonnd finat fie effectiveess of fiemaasdspendsntonfietypeofemlsifierused, fieanountof ennulsifier added, and fie herbicide. Several superior experimental adjuvents, based on l4C-sefinoxydim absorptionvalues, increasedsefiexydinncontrol ofquackgrassinfie field (Table 1) . POC-A97 and soc-A297 were found to shim ssfino-nydimactivityonquackgrassconparedtofiecontrol providedby fiestedardCDCorASA—SBOCB. I-Ionever, fieexperinnsnntal surfactents were slightly less effective for sefiexydim then fie experimental POC or SOC (Table 1). Tie interaction between surfactant and oil types were also apparent in fie field. Experimental surfactant A50 was none effective 7medesignationafterthehyptenreferstotheexperinmtal surfactantincludedinfiePOCorSOC. 8ASA-SBOC is a product of American Soybean Association. 59 inenhanncingquacl-ngrasscontrolwithsefiexydinnwhenappliedasa conponentofPOCorSOCfinanasasurfactant(Table1). Loweringfine sprayvolunefronnl40 L/hato65 L/ha, whilemaintainningfiesane enount of adjuvant, significantly increased sefincxydim activity on quackgrass. ThisisconsistentwifinfieweviousreportsbyKellsand Wanenarta (1986), Dexter et al.(1984), end Buhler and Burnside (1984). Smaller end more coeentrated sefincxydim droplets were more phytotoxic to sorghum finen larger and nere dilute droplets (Buhler end Burnside, 1984). Bentazon spray droplet sweadability fron a bentazon sway solutionhadamaxinnunnsweadonnlmonlanbsquarter leaves (Appedix Table 5). Of 90 experimental adjuvants tested for bentazon additive, fie droplet spreadability of bentazon sway solutions varied front 1 nm to 31 am on lanbsquarter leaves (Appendix Table 5-7). Whenl4C-ben‘tazonabsorptionwasnneasued, fieuptakeofbentazon wifieut an adjuvannt was 31% of finat applied (Ame'dix Table 5). Additionoffiemc, Herbimax, andfiestandardSOC, ASA-SBOC, bofinat fie recomended rate of 2.4 L/ha, increased 14C-benntazon absorption to 67% end 72% of fie applied, respectively (Appedix Table 6-7) . Addition of fie experimental adjuvants to bentazon sway solution woduced 14C-bentazon absorption reging fronn 4% to 86% of fie applied (Appendix Table 5-7). The best adjuvant was identified as the surfactant B5 (Appendix Table 5). 'Ite results also indicated finat sore experimental adjuvants were worse finan ne adjuvant added, with respect to 14C-bentazon absorption by lambsquarter leaves. Thus, adding fie inappropriate adjuvant may reduce bentazon phytotoxicity. 60 Plotting bentazon may droplet sweadability data wifin fie absorption data revealed a close relatioehip between fiese two factors (Figure 2). Thus, neasuring bentazon droplets swead on fie targetweedappearedtobseneasy, rapid, andinexpennsivenefiedof adjuvant screening for bentazon. Differential responses of sefiexydim end bentazon to fie enpsrimental adjuvantsmaybsduetofiediffereesinherbicidssnede ofactionendtranslocationpattern. Sefiexydim, oeeabsorbsdbya leaf, will be trannslocated finronghout fie plant: (Wills, 1984). In contrast, bentazonnovenentisverylimitedanditactsasacontact lerbicids (Mahoey end Penner, 1975). It has been docunented finat hignersprayvolunes, whichneannsnerespraycoverage, einanced bentazon activity (Kapusta and Onaney, 1984). Thus, an increase in contact between bentazon spray droplets and lenbsquarter leaves enhanced bentazon absorption and activity. Tte efficacy of adjuvants for inclusion inn a bentazon spray solutionwerenetinfluencedbyoiltypssasnuchasfiesurfactants for sefiexydim. Surfactents ideal for adjuvant use wifin bentazon were identicaltosurfactantsidsalasconponentsofSOCorPOC (Appendix Table 5-6). Addition of superior experimental adj uvants signnificently increased bentazon activity on lanbsquarters in fie greenhouse (Table 2). me experimental adjuvants pee-13307 and pee-1357 were more effective finen fie standard (13C, Herbinnax. However, ne differecs in efficacywasdstsctsdbstweenfieexperinentalSOCsandfiestandard SCI}, ASA-SEE (Table 2). 61 In 1984, experimental adj uvants POC-BS and SOC-B5 significantly increasedredrootpigwesdcontrolwithbentazoninfiefisldconpared to fie regular CDC (Table 3). Tie surfactent BS did net enhance bentazon activity probably due to a surface run-off of fie herbicide droplets fron fie weed leaves. Surfactant B5, used as an adjuvannt, had nuch greater spray droplet spreadability on lambsquarter leaves finann obtained by blending it wifin oils to form crop oil cocentrates (Appedix Table 5-7). 'I'ne BS surfactant was also oe of fie least effective adjuvent on lenbsquarter in fie greenhouse (Table 2). In 1985, fie efficacy of fie experimental adjuvant B30 on bentazon activity in fie field was net apparent (Table 4). Tie differeceinbentazonresponsetofieadjuvantsinfiefiwoyearsmay bsduetofieunfavorablegrowingconditions (retenddry) in1984, in contrast to nere favorable growing coditions in 1985. Nbisture stress in 1984 would wonete developnent of less pernleabls cuticle, whichmayexplainfieenhancedbentazon activitywifinfieexperimsntal adjuvents. For fie 1985 growing coditions, a bentazon rate of 0.84 kg/ha was possibly too high to observe fie adjuvent effects. In fie greenhouse, wterefiegrowingcoditionsresultedinafininnercuticle (Hull, 1958), 0.28 kg/ha or 0.56 kg/ha of bentazon caused too much injury on larbsquarter to detect fie adjuvant efficacy (Appedix Table 8—9). Nalewaja et al. (1984) also neted finat fie beefit fronn oil additivestopostenergecebentazontreabnentwasdependentupon enviromental coditions. They noted that oil additives enlneced weed control wifin bentazon in dry climatic coditions. 62 In conclusion, fie study indicated finat fie ability of en adjuvant to wet fie target weed leaves and to woncte lerbicids peetration depedsd upon fie lerbicids, surfactant, and oil used. Tlerefore, identification of fie apwopriate adjuvant for a specific herbicide use is very important to obtain maximum lerbicids activity. 63 O n— .9 0 ID 0 A . . E v e e e o e e .o .0 . O 8 I. . 00 e bl") Q. o e. .00 e m o a e e - e e o e e o n ...-w e e 0 so a e ... . e. . ee ... . e a no a e e e o e -S O o e e e e e h e e . ..e O o e. e e b O 0 O. b .0 e - u e 0 ee 0 - e e . e e e... . _O o e e e e "’ 00 Q- .0000 e a e e P O. b o e a O O O O O Q 0 V N (pauddo o z) DGQJOSQD MP XOHPS-On Figure 1. Relationship between droplet spread and l4C-sefiexydinn absorption on quackgrass as influenced by adjuvants. 64 Tablel. Effectofseveralselectedenperinentaladjuvanntsonsefiexydim acti.vityinfiefieldinl985. Sway Qnadgrasscontrol a Volune Treatment 33M 110DAT (L/te) ....... (%) ....... Sefiexydim 140 780 87bc Sefiexydim-n-CEI: 140 89$ 87hr: +ASA-SHI: 140 89$ 85c +A50 140 91$ 84c +A29 140 92$ 88bc +137 140 90$ 89bc +PCII-A50 140 89$ 92$ +P(I:—A29 140 94$ 89bc +P(I:-A9 140 97a 96$ +SCIZ-AE) 140 89$ 13$ +312-A29 140 94$ 95ab +soc-A49 140 88b 83c +D’7 65 97a 97a 65 Tablelontined. + HIE-A50 65 96 $ 99 a +soc-A29 65 95$ 983 a SefiexydimedsnrfactentsweeagpliedatO.56l-ng/Ieadl.2L/te, respectively. (III, ASA-8m, HIS, edscxtverearpliedatZA L/le. mongoflcoeentratetebinax,awod.ctoflhionmrbide. ASA-SEIkstedardar,awodctofAnericanSoybeanA-sociation. SEmefionmlatadbynfindngBfiperaffiniccrswbeanoilsvdfinM surfactant. b Nnnbersfollowedbyfiesanelettersudfininacolnnnarenet signnificsnntlydifferentatfiefilevelusinghrcen'sMnltiplsRage Test. medaysafberfieatnert. c rliedesignntntionfollowingfiehynienreferstnnfieennperinentsl snrfactsntfoumlatsdwifinfiemcrsm. Figure 2 . 66 C) V 1 fi' 1 V l j I 1 ¢ . L e . . -9, 3 n » E 13 0 C! C) CD - I.“ a an ' ea .2 b '- Q C) L D n. 100 (pauddo no r) DOQJOSQD uozonuaa—o» Relationship between droplet spread and 14C-bentazon absorption on lambsquarters as influenced by adjubants. 67 TableZ. EffectofselectedadjuvontsonbenntszonactiyityatOJIIvg/haon lantequarter in fie greatness. b a Injury Fresh weignt Treatment rating (%) (Q/pUt) Chntrol 0 g 16.4 a Bentazon 0 g 17.6 a m + (II: 20 f 8.5 b + ASA-SKI: 40 d 7.1 be + BC!) 60 b 5.5 cd + PCB-BC!) 50 c 5.3 cd + soc-Boo 30 e 7.4 be + BS 30 e 8.8 b + PCB-BS 70 a 3.1 d + SKI-B5 50 c 6.1 bc a Bentazonedsnrfactanntweneqpliedato.llkg/neadl.2L/ha, respectively. (III, ASA-SEE, PCB, adSEwereagnliedatZA L/le. CIDcnrpoilcoeentrateHsrbinnen,awodctofIhionCarbinb. ASA-SHIkstedardm,awodctofAnericunSoybeanAsociation.m paraffinnicoilcoeentnate,$(13=snybeanoilcreenntrate. Modal: veefonmlatedbymindng80%paraffiniccilorswbeanoiland20% surfactant. BSedmemnentalsnfactants. 'Itedasignation follodngfiehypenrefestofieenperinentslsurfactantfomulatsd wifinfieFCIJadan. b Nnnbersfollowedbyfiesaneletter,wifininacolmn, arenot significantlydifferentatfilenelusinghxeen‘sMnltfipleRageTest. 68 Tabmeil. Effirxchneflactaiemperflmafirfl.adynmrrs<3ntentaarnacriuflqwin fie field in 1984. a rate control 1183111311: 13 DAT 35 DAT (L/ha) ....... (%) ....... Bentazon + HIE-B5 2.4 73 a - + SCIZ-BS 2.4 72 a - + ASA-SKI: 2.4 70 $ - Bentazon - 53 c - + (II: 2.4 50 c - + BS 1.2 40 d - BentamnwasqpliadatO.84kg/ha. morpoiloreenntrateHerbinec, awodnctofunioncarbine. ASA-Wsmmrdar,awmctd kneicanScybeanAssnciation. maybeanoilcocenoate,m paraffinniccilcreenntrate. SEadRIIwerefcrnulatedtyndndngfl scybeanoilcrparaffinicoilwifinZRsnrfactent. BS=experinental surfactant. 'Inedasignationfonowingfielypenreferstbfie eminentalsnrfactanntfcrnnnflatedwifinfiemcrar. b Nnnbersfollowsdtyfiesanelettesaremtsiguficontlydfferentat fie5%levelusingDur:an'sMnlfi.p1eRage'Iest. DAT=<>> " ”‘87? " U'ZEZ " U'QIZ NW E - °>xox b w m .0000000000o 20N<~2wn .02 .II‘I ZON<~annoz .... E.O>x02~wm 0000000000000000000 000 AV o 1f 93.. 88.: Sand 5s. .N (OmOKAh—Oz UV Spectra of setlnoxydim, Na-bentazon, and the mixture of sethoxydl'm and Na-bentazon. Figure 2 . 92 Table 5. Effect of Na-bsntazon on ssfinoxydim polarity. l4C-Ssfinoxydim found in: Treatment6 Me.C12 Et.Ac. HZO (% of applied) Ssfinoxydim + (DC 23 c 74 a 3 b Sefinoxydim+CDC+Na—bentazon 41b 44b 15a Ssfinoxydim + D7 55 b 45 b 0 b Ssfinoxydim+D7+Na—bentazon 80a 19c 1b a Ssfinoxydim, Na-bsntazon, (13C, arnd D7 were applied at 0.56 kg/ha, 0.84 kg/ha, 2.4 L/ha annd 4.8 L/ha, respectively. D7= experimental surfactant. b anc= Crop oil concentrate MeClZ= msfinylee chloride, Et.Ac= sfinyl acetate, HZO= water solution Nunbsrs followsdbyfieselelettsrswifininacolumaremt significantly different at fie 5% level using Duncan's Multiple RangsTsst. 93 Table 6. Effect of Na—salts of strong and weak conjugate bass on sefinoxydim absorption. Treatnenta 14C-Sefinotxydimabsorbedb (%ofapplisd) Ssfinoxydim+CDC 60b Ssfinoacydim + CDC + Na-bsntazon 31 c Ssfimydim+£DC+lOnMNaCl 62b Ssfiquim+CDC+100nMNaCl 86a Sefinoxydim+=enybeanoiloreentrate. moaosoc werefiomulatedtynnindngflparaffinicdlo‘sybeanofladfl surfactant. B5andB3)=eqerimntalsnrfactants. b Nnnbersfollonedtyfiesanelettenvdfininaoolmn, arenet significannflydifferentatfilevelnsingmmn'sMJlfipleRageTest. 166 AmedixTablelO. EffectoffieC-seriessnrfactartonsefimnydimad Ala-bentazoninnteraction. a qunlet 140-8630152611“ Treatnent spread alerted (mm) (%ofanplied) Sefirrnydim+Na-benoazon+c32 7d 66a +C26 4% 26b +C31 5oz 22c +C27 12c 21c +C12 6th 19c +Cl9 5th 19o! +C3) Sch 17d +C6 4th 17d +C17 4th 17d +C21 4Cb 17d +C11 5m 1663 +C13 6th 16