The adsorption from chloroform solution of the herbicide diclofop, (RS)-2-(4-(2,4-dichlorophenoxy)phenoxy)propionic acid, and its methyl ester diclofop-methyl on Cu2+-, Al3+-, and Fe3+-exchanged bentonite samples was investigated. For comparison, the complexes formed by diclofop were synthesized and studied. Diclofop adsorbed on the clays and formed carboxylate bonds to the interlayer ions. Diclofop-methyl also adsorbed, but its interaction involved the formation of hydrogen bonds with water molecules in the interlayer. Traces of diclofop were observed in both the solution and the clays after adsorption of diclofop-methyl, indicating that some hydrolysis of the ester to the corresponding acid occurred. Thus, pesticides forming neutral complexes with interlayer cations in montmorillonite in soils may be extractable by solvents and therefore released into the environment.

Twelve sequential herbicide treatments were compared to cycloate (S-ethyl N-ethylthiocyclohexanecarbamate), a standard treatment, for control of annual weeds in sugarbeets (Beta vulgaris L.) in three field experiments conducted from 1971 through 1977. At harvest, seven sequential treatments had less than 10 annual broadleaf weeds per 30 m of row, whereas there were 40 broadleaf weeds per 30 m of row for the cycloate treatment. Four of these sequential treatments had significantly higher root yields and net returns than the cycloate treatment. Dependent on the sequential treatment and year, tonnage was increased 7.3 to 20.3 t/ha, and net returns $150 to $515/ha above those with cycloate. The most effective sequential treatment for control of weeds was a preplanting mixture of 2.2 kg/ha of ethofumesate [(±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate] plus 1.7 kg/ha of diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} followed by a postemergence mixture of 0,6 kg/ha each of desmedipham [ethyl m-hydroxycarbanilate carbanilate (ester)] plus phenmedipham (methyl m-hydroxycarbanilate m-methylcarbanilate). This sequential herbicide treatment increased root yields by an average of 20.3 t/ha and net returns by $515/ha above those with cycloate.

In field studies trifluralin and pendimethalin at 1.7 kg ai ha-1 applied PPI controlled itchgrass 87 and 78%, respectively, in late season when averaged over a 2-yr period. Clomazone at 1.1 kg ai ha-1 applied PRE to the soil surface in one year controlled 80% of itchgrass compared with 51% when applied PPI. POST application of 0.15 kg ai ha-1 fluazifop-P, 0.21 kg ai ha-1 haloxyfop, 0.10 kg ai ha-1 quizalofop, and 1.1 kg ai ha-1 diclofop controlled at least 90%. Itchgrass control was less effective with 0.43 kg ai ha-1 sethoxydim and 0.07 kg ai ha-1 clethodim POST and poor with 0.15 kg ai ha-1 imazaquin and 0.07 kg ai ha-1 imazethapyr.

The effects of 14 herbicide treatments, tested in the establishment phase, were investigated on timothy productivity in two field experiments conducted at Melfort, Saskatchewan. Satisfactory weed control achieved with chlorsulfuron, metsulfuron, thifensulfuron, bentazon, diclofop plus bromoxynil, and MCPA/mecoprop/dicamba during the establishment year ensured good forage establishment which in turn caused a ‘residual effect’ for 1 to 3 yr increasing individual cut as well as cumulative forage dry matter yields significantly. In the stand established in 1985, when field pennycress (97 m-2) was the dominant weed in the seedling stage, these treatments increased yields 29 to 52% over a 3-yr period. In the stand established in 1986, when common lambsquarters (27 m-2) was the dominant weed, these treatments increased cumulative yields 24 to 44%. Sethoxydim and fenoxaprop, tested alone, caused significant crop injury in both experiments.

‘Karla’, ‘Klages', ‘Morex’, and ‘Steptoe’ cultivars of spring barley (Hordeum vulgare L.) differed in susceptibility to postemergence recommended application rates of diclofop {(±)-2-[4-(2,4-dichlorophenoxy) phenoxy] propanoic acid}, difenzoquat [1,2-dimethyl-3,5-diphenyl-1H-pyrazolium], chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide}, and metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] in 1981 and 1982. Metribuzin injured Morex, and difenzoquat injured all cultivars within 2 weeks after herbicide application. Metribuzin reduced height and crop biomass compared to the hand-weeded control. Herbicide treatments did not affect grain yield at Moscow, ID, in either year. However, metribuzin reduced yield of Karla and Morex, and diclofop reduced yield of Karla compared to the hand-weeded control at Pullman, WA, in 1982. Barley injury and grain yield loss depended on herbicide treatment and cultivar. Early season herbicide injury to barley did not indicate grain yield response at harvest.

Field studies were conducted to document the response of itchgrass [Rottboellia exaltata (L.) L.f. ♯3 ROOEX] in soybean [Glycine max (L.) Merr. ‘Forrest’] to selected herbicides and postplanting cultivation. Early cultivation stimulated emergence of itchgrass seedlings; however, when plots were cultivated two or three times, itchgrass was effectively removed from the tilled area. Cultivation had no effect on the density, height, standing biomass, or seed production of itchgrass plants in the soybean row but did increase soybean yield. In response to a density reduction of 90%, the average weight, number of tillers and branches, and seed production of single itchgrass plants increased by a factor of 2.9, 3.1, 2.3 and 2.6, respectively, in trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine)-treated plots. Individual plants did not increase growth following density reduction by a postemergence application of diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid}. Itchgrass plants competing for the entire season in plots treated with trifluralin reduced soybean yield approximately 21 g per weed, while itchgrass recovering from diclofop treatment and competing the remainder of the season reduced yield approximately 5 g per weed.

Colletotrichum gloeosporioides f. sp. malvae (C.g.m.) was evaluated under greenhouse conditions for round-leaved mallow control in combination with the following herbicides: bromoxynil plus MCPA (1:1), diclofop, imazethapyr, metribuzin, sethoxydim, and 2,4-DB. Treatments consisted of C.g.m. and herbicide applied alone, tank mixed, and C.g.m. applied 48 h before, and 1, 24, and 72 h after herbicide. Split applications with bromoxynil plus MCPA, imazethapyr, metribuzin, (C.g.m. before or after) and sethoxydim (C.g.m. before) enhanced round-leaved mallow control over C.g.m. applied alone. However, diclofop or 2,4-DB tank mixed or applied in a split application with C.g.m. did not improve round-leaved mallow control over C.g.m. applied alone. Bromoxynil plus MCPA, metribuzin, 2,4-DB, and imazethapyr may be tank mixed with C.g.m. without significantly reducing round-leaved mallow control, unlike sethoxydim or diclofop which inhibited C.g.m. development. Dew period did not influence the effectiveness of bromoxynil plus MCPA applied 30 h before C.g.m., but round-leaved mallow control increased with increasing dew period for metribuzin applied 30 h before C.g.m.

The goal of this research was to determine whether crop management practices could substitute for a herbicide for managing mixed populations of green and yellow foxtail in hard red spring wheat. Crop yield and foxtail growth were measured in two years of field research in North Dakota. Spring wheat yields were as great or greater when early seeding date or 2× seeding rate were substituted for POST diclofop3 at 0.75 kg ai ha−1 for managing foxtail in spring wheat. Yield of spring wheat competing with foxtails was greater for the high seeding rate (2× = 270 kg ha−1) than both the normal (1× = 130 kg ha−1) and low (0.5× = 70 kg ha−1) seeding rates for early or middle seeding dates, but not for the late seeding date. For both early and middle seeding dates, wheat yield at the 2×seeding rate without diclofop was equal to or greater than that of the 1× seeding rate with diclofop. Late-seeded wheat did not yield well in competition with dense foxtail stands for any treatment combination. Early and middle seeding dates favored the relative increase of green foxtail over yellow foxtail in wheat, whereas late seeding favored yellow foxtail over green foxtail. Economic analysis demonstrated that early seeding date was the most critical factor in determining the stochastic dominance of treatments without diclofop over treatments with diclofop. Seeding rate was much less important than seeding date in determining the ranking of treatments in stochastic dominance analysis.

Inheritance of resistance to diclofop was studied in three wild oat biotypes (designated B, C., and H) from the Willamette Valley of Oregon. Cultivated oat (cultivar ‘Monida’) was crossed, including reciprocals, to three wild oat biotypes. Leaves of each F1 plant were spotted with diclofop as a nondestructive test for resistance or susceptibility. All F1 hybrids were resistant, indicating that resistance is dominant and is under nuclear control. The F2 plants where Monida was the maternal parent were screened with diclofop, and F2 plants of the Monida/C cross were screened with fenoxaprop because the parent C biotype was resistant to fenoxaprop. At lower doses, a 3:1 (R:S) segregation ratio in F2 was observed and at higher doses a 1:3 (R:S) segregation ratio was often observed. The F2:3 families segregated in a 1:2:1 (all resistant : segregating resistant and susceptible all susceptible) ratio when treated with a 1.1-kg ae ha−1 dose of diclofop. This confirms that resistance to diclofop in the B, C, and H biotypes is primarily under monogenic control, with resistance being dominant to susceptibility at lower herbicide doses. At increased doses, susceptibility becomes dominant. Knowledge of the inheritance of resistance may help in the development of containment measures to prevent the spread of herbicide-resistance genes.

Near isolines of ‘Nugaines’ winter Triticum aestivum that differed in height were planted with and without Aegilops cylindrica to determine the effect of plant height on competition against A. cylindrica. The isolines had either reduced height gene Rht 1, Rht 2, Rht 1 plus Rht 2, or neither Rht genes and averaged 79, 77, 51, and 101 cm tall, respectively, when grown with or without competition from A. cylindrica. Plants with fewer reduced height genes had the faster rates of height and weight gain, which are important traits for enhanced competitiveness. When growing in competition with A. cylindrica, the shortest isoline allowed the greatest amount of A. cylindrica seed production but did not have the lowest T. aestivum yield. However, when compared to the A. cylindrica-free control, the shortest isoline had the greatest percent yield loss. The tallest isoline reduced A. cylindrica seed production the most, and T. aestivum yield reduction due to A. cylindrica on a percent basis was the least when averaged over 2 yr. When competing against A. cylindrica, the tallest isoline did not always have the largest yield and yield parameters, and the shortest isoline did not always have the smallest yield and yield parameters. There is a cost to the T. aestivum plant to produce extra stem biomass that may reduce yield potential of taller plants and reduce the advantage gained by being taller than the surrounding weeds.

Postemergence applications of MSMA (monosodium methanearsonate) for weed control in spring wheat (Triticum aestivum L.) were evaluated in the field, greenhouse, and controlled environmental chamber. MSMA controlled weeds better when applied to wheat at the four- to five-leaf stage than when applied at the two- to three-leaf stage. MSMA, tank mixed with barban (4-chloro-2-butynyl-m-chlorocarbanilate) or diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid}, controlled wild oat (Avena fatua L.), green foxtail, [Setaria viridis (L.) Beauv.] and broadleaf weeds better than did MSMA applied alone. Wild oat control with tank-mix applications of MSMA and difenzoquat (1,2-dimethyl-3,5-diphenyl-1H-pyrazolium) was variable. Weed control with MSMA was enhanced by 30 C air temperatures, 90% relative humidity, and adequate soil moisture. A simulated rainfall of 0.5 mm within 0.5 h or 4 mm with 4 hr after application reduced wild oat control with MSMA.

Retention, absorption, translocation, and volatility of foliarly applied diclofop-methyl {methyl 2-[4-(2,4-dichlorophenoxy) phenoxy] propanoate} were compared in barnyardgrass [Echinochloa crus-galli (L.) Beauv.], a susceptible grass; proso millet (Panicum miliaceum L.), a moderately susceptible grass; longspine sandbur [Cenchrus longispinus (Hack.) Fern.], a tolerant grass; and soybean [Glycine max (L.) Merr. ‘Hark’] and cucumber (Cucumis sativus L. ‘Green Star’), both tolerant broadleaf plants. On a jug/plant basis, the order of diclofop-methyl spray retention was cucumber > soybean > proso millet > longspine sandbur = barnyardgrass. On a μg/mg dry weight basis, proso millet retained 3 to 10 times more diclofop-methyl than all other species. One day after treatment (DAT), absorption of 14C-diclofopmethyl was 14 to 18% less in longspine sandbur than in the other species, 3 DAT absorption in cucumber was 8 to 14% greater than in the other species, and 5 DAT absorption in soybean was 3 to 12% less than in other species. Translocation of 14C-diclofop-methyl did not differ among species, with 98% of the applied radioactivity located in the treated leaf. An average of 11% of radioactivity applied to the surface of intact, living plants and excised, dried leaves of cucumber, soybean, and barnyardgrass, as well as glass cover slips, was lost by evaporation. None of the parameters measured showed differences large enough to be implicated as primary selectivity mechanisms.

Field experiments were conducted in Thessaloniki, Greece, from 1991 to 1994 to study the competition of littleseed canarygrass and short-spiked canarygrass biotypes in wheat and to evaluate their response to diclofop, fenoxaprop, tralkoxydim, and CGA-184927. Competitive ability of all canarygrass biotypes was similar, though species differed in panicle numbers. All littleseed canarygrass biotypes showed faster growth rate than the short-spiked canarygrass biotypes. Wheat grain yield decreased as canarygrass density increased. For example, 152 and 304 canarygrass plants m–2 reduced wheat yield 32 and 42%, respectively. None of the canarygrass biotypes at any density had any effect on grain yield of wheat when cold and dry weather prevailed during the early stages of growth. CGA-184927 and tralkoxydim were more effective herbicides against all short-spiked canarygrass biotypes than fenoxaprop and diclofop. CGA-184927 and fenoxaprop provided > 98% control of all littleseed canarygrass biotypes; control with tralkoxydim was < 80%; and diclofop gave 82 to 96% control of this weed species. Herbicide control of canarygrass increased wheat yield relative to the weedy control, and only diclofop was phytotoxic to wheat.

Sethoxydim {2-[1-(ethoxyimino)-butyl]-5-[2-ethylthio)propyl]-3-hydroxy-2-cyclohexene-1-one}, KK 80 {ethyl-4-[4-[4-(trifluoromethyl)phenoxy] phenoxy]-2-pentenoate}, and RO-13-8895 {acetone-0-2-[D-2-[δ,δ,δ-trifluoro-p-tolyl)-oxy] phenoxy] propionyl] oxime} did not injure plants visibly or reduce the yield of tomatoes (Lycopersicon esculentum L.). Diclofop LC [2,4-(2,4-dichlorophenoxy)phenoxy] propanoic acid] and diclofop HC in combination with oil or surfactant reduced tomato yield because tomatoes retained more of these spray solutions. No herbicide treatments injured onions (Allium cepa L.). All compounds controlled most grass weeds. Tomato plants grown at 29/18 C were injured more by some diclofop treatments than plants grown at 18/7 C. Cell membrane permeability of tomato plants treated with diclofop alone or in combination with adjuvants increased as visual injury symptoms became more severe.

Field experiments were conducted in 1982 through 1986 to evaluate the effect of six postemergence grass herbicides, clethodim, the methyl ester of diclofop, the butyl ester of fluazifop-P, the methyl ester of haloxyfop, the methyl ester of quizalofop, and sethoxydim, on 31 seedling grass species. All herbicides except diclofop controlled most of the species tested. None of the herbicides controlled rattail fescue or red fescue. Only clethodim and haloxyfop controlled annual bluegrass.

Greenhouse studies were initiated to identify potential interactions of the postemergence herbicide acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} with the postemergence grass herbicides sethoxydim {2-[1-(ethoxyimino) butyl]-5-[2-(ethylthio) propyl)-3-hydroxy-2-cyclohexen-1-one}, diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy]propanoic acid}, and RO-13-8895 [acetone 0-(D-(2-(p-[(α,α,α-trifluoro-p-tolyl)oxy) phenoxy)propionyl)oxime}. Greatest control of barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG] was obtained with the combination of acifluorfen and sethoxydim plus a crop oil concentrate. This combination increased foliar absorption of 14C-acifluorfen by barnyardgrass but not by soybean [Glycine max (L.) Merr. ‘Corsoy’]. The combination of acifluorfen with diclofop appeared to reduce phytotoxicity to barnyardgrass and increase it to soybean. Little or no interaction was observed in combinations of acifluorfen and RO-13-8895.

Research was conducted on a sandy clay loam in Georgia during 1987–88 and 1988–89 to determine winter wheat, oats, barley, and Italian ryegrass tolerance to flurtamone. Flurtamone was applied PPI, PRE, and early POST at 0.28, 0.56, and 1.1 kg ai ha-1. Order of tolerance of the four species was barley > wheat > oat > Italian ryegrass. Flurtamone potentially can be used to control Italian ryegrass in winter wheat and barley, but not in oats. In general, wheat and oat injury with flurtamone was PPI > PRE ≥ early POST, particularly at 1.1 kg ha-1.

Field experiments evaluated barnyardgrass, broadleaf signalgrass, and rhizomatous johnsongrass control with sethoxydim, clethodim, fluazifop-P, quizalofop-P, and fenoxaprop applied alone and with bentazon or chlorimuron when crop oil concentrate or BCH 815 was used. Bentazon strongly antagonized sethoxydim and clethodim. BCH 815 partially reduced the antagonism with sethoxydim and clethodim compared with crop oil concentrate. Chlorimuron was most antagonistic towards fluazifop-P, fenoxaprop, and quizalofop-P, and BCH 815 did not reduce antagonism. Additional experiments evaluated Italian ryegrass control with diclofop applied alone and with bromoxynil, metribuzin, 2,4-D amine, or tribenuron plus thifensulfuron with these adjuvants. The amine formulation of 2,4-D and tribenuron plus thifensulfuron reduced Italian ryegrass control with diclofop, irrespective of the adjuvant.

Sugarcane (Saccharum officinarum L.) was planted in the fall; the seed cane was healthy or infected either with sugarcane mosaic virus (strain H) or with ratoon stunting disease (RSD) (Clavibacter xyli). Herbicide treatments were applied the following spring and each subsequent spring during the 3-yr crop cycle. Hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione] at 1.1 kg ai/ha was applied as a soil foliage treatment when sugarcane was about 30 cm tall. The methyl ester of diclofop {(±)-2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} at 1.1 kg ai/ha and the sodium salt of asulam {methyl [(4-aminophenyl)sulfonyl] carbamate} at 3.4 or 3.8 kg ai/ha were applied as foliage treatments when sugarcane was about 90 cm tall. Both mosaic and RSD reduced yield of sugar/ha by 16% for the 3-yr crop, primarily by causing a decrease in stalk population. Hexazinone reduced yield of sugar/ha by 24% primarily by causing a decrease in both stalk population and sugar content of stalks. Diclofop reduced yield by 7% and asulam caused no significant yield loss. Combinations of disease and herbicide treatment reduced yields in an additive manner, with the combination of hexazinone and either mosaic or RSD causing a 38% reduction.

Three triazine-resistant biotypes of grass weeds, hood canarygrass (Phalaris paradoxa L. # PHAPA), ryegrass (Lolium rigidum Gaud.), and slender foxtail (Alopecurus myosuroides Huds. # ALOMY) were collected along roadsides on the coastal plain of Israel that had been treated repeatedly with s-triazine herbicides. Resistant biotypes (R) survived up to 4 kg ai/ha of atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine] applied pre-and postemergence, while susceptible (S) biotypes were killed by 0.25 kg/ha. R and S biotypes were equally sensitive to diuron [N′-(3,4-dichlorophenyl)-N,N-dimethylurea]. Electron transport in chloroplasts isolated from R biotypes was not affected by atrazine, whereas in S biotypes electron transport was inhibited 50% by 0.4 to 1.0 μM atrazine. Chloroplasts from both biotypes were equally sensitive to diuron. These data indicate that the R biotypes have a plastidic mode of resistance to atrazine. In addition, seedlings of R biotypes exhibited resistance to triazinone herbicides. The R biotype of hood canarygrass was more tolerant to postemergence application of diclofop {(±)-2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid}.