Research was conducted from 1983 through 1985 in east central Texas to determine the effect of grass-specific herbicides, herbicide rates, and weed height on johnsongrass [Sorghum halepense (L.) Pers. #3 SORHA] control and cotton (Gossypium hirsutum L. 'Stoneville 825’) yield. Seven herbicides were applied to johnsongrass less than 30 cm tall with 2 to 5 leaves approximately 4 weeks after cotton emergence. Good-to-excellent johnsongrass control was observed for each herbicide except cloproxydim {(E,E)-2-[l-[[(3-chloro-2-propenyl)oxy]imino] butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} at 0.56 kg ai/ha and sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} at 0.28 kg ai/ha. Few significant differences were found in seed cotton yields even though johnsongrass control ranged from 43 to 99% 26 days after treatment (DAT). These data suggest that johnsongrass regrowth and/or reinfestation following initial control of 75% or higher during the first 4 to 6 weeks after cotton emergence has a minimum negative effect on cotton yield. Johnsongrass control was highest when either fluazifop-P {(R)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy]propanoic acid} or haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy] propanoic acid} was applied to 15 to 30 cm tall johnsongrass.

Six postemergence herbicides were applied two consecutive years in single and split applications to compare johnsongrass [Sorghum halepense (L.) Pers. # SORHA] control in soybeans [Glycine max (L.) Merr.] planted in 25- and 76-cm inter-row spacings. Significantly less johnsongrass existed at harvest in the 25-cm spacings than in the 76-cm spacings with split applications of fenoxaprop {(±)-2-[4-[(6-chloro-2-benzoxazolyl)oxy] phenoxy] propanoic acid} at 100 g ae/ha, fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} at 100 g ae/ha, sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} at 200 g ai/ha, and SC-1084 {3-hydroxy-4-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] pentanoic acid} at 250 g ae/ha. Quizalofop {(±)-2-[4-[(6-chloro-2-quinoxalinyl)oxy] phenoxy] propanoic acid} at 70 g ae/ha and haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} at 100 g ae/ha controlled johnsongrass so well that differences between the two row spacings were not significant.

The effects of rainfall on the efficacy of 11 foliar-applied herbicides were evaluated for their control of seedling johnsongrass [Sorghum halepense (L.) Pers. # SORHA] in greenhouse experiments during 1984 and 1985 at Stoneville, MS. Time intervals between herbicide application and rainfall (at 1.27 cm in 10 ± 0.5 min) ranged from 5 to 60 and 30 to 240 min depending on herbicide classification. In general, the phosphonic acid herbicides glyphosate [N-(phosphonomethyl)glycine] and SC-0224 (trimethylsulfonium carboxymethylaminomethylphosphonate) at 0.99 kg ai/ha required rain-free periods ≥240 min to control seedling johnsongrass effectively. The selective postemergence grass herbicides generally required ≥60 min to control seedling johnsongrass effectively when control without rainfall was ≥85%. Among the selective herbicides tested, haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl]oxy] phenoxy] propanoic acid} and DPX-Y6202 {ethyl[2-[4-(6-chloro-2-quinoxalinyl)oxy] phenoxy] propionic acid} at 0.06 kg ae/ha required the shortest time between herbicide application and rainfall to be effective. As herbicide rates were reduced, the effects of rainfall increased.

A rainfall simulator was used to evaluate the effects of washoff on 10 foliar-applied herbicides on johnsongrass [Sorghum halepense (L.) Pers. # SORHA] in greenhouse experiments during 1983 and 1984 at Stoneville, MS. Time intervals between herbicide application and rainfall ranged from 20 to 240 min. Johnsongrass topgrowth control was equivalent to rain-free treatments using DPX-Y6202 {ethyl [2-[4-(6-chloro-2-quinozalinyl)oxy] phenoxy] propionate} at 0.03 and 0.06 kg/ha at time periods of 90 and 40 min between herbicide application and rainfall, respectively, at 28 days after treatment (DAT). A period of 120 min was required for johnsongrass control equivalent to rain-free treatments using sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} at 0.06 kg/ha, haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl]oxy] phenoxy] propanoic acid} at 0.03 and 0.06 kg/ha, and cloproxydim {(E,E-2-[1-[[(3-chloro-2-propenyl)oxy] imino] butyl]-5-[2-ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} at 28 DAT. Neither glyphosate [N-(phosphonomethyl)glycine] and SC-0224 (trimethylsulfoniumcarboxy methylaminomethylphosphonate) at 0.45 and 0.99 kg/ha nor other selective herbicides at 0.03 and 0.06 kg/ha gave equivalent johnsongrass topgrowth control to rain-free treatments when rainfall occurred within 240 and 120 min, respectively.

Selective postemergence herbicides were applied broadcast to control wild-proso millet in soybeans early postemergence (early post), postemergence (post), and late postemergence (late post) when wild-proso millet was 2 to 8 cm tall, 3 to 15 cm tall, and 3 to 31 cm tall, respectively. CGA-82725, fluazifop, haloxyfop, and sethoxydim applied early post controlled 75% or less late-season wild-proso millet. Interrow cultivation following early post fluazifop applications improved wild-proso millet control and soybean yields. Higher rates of CGA-82725, haloxyfop, and sethoxydim applied post controlled 91 to 98% late-season millet, but resulting soybean yields were less than the hand-weeded check. Fenoxaprop, fluazifop, fluazifop-P, haloxyfop, quizalofop, and sethoxydim applied late post provided 93 to 99% late-season millet control and soybean yields equal to hand-weeded checks. Wild-proso millet emerging after early post or post herbicide applications contributed to reduced effectiveness from those treatments. However, most wild-proso millet emerged before late post applications and were controlled. Other herbicides including BAS-51702, clethodim, cloproxydim, and SC-1084 applied late post also controlled wild-proso millet in soybeans.

Sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio) propyl]-3-hydroxy-2-cyclohexen-1-one} at 0.34 kg ai/ha, fluazifop {(+)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} at 0.13 kg ai/ha, and SC-1084 {3-hydroxy-4-[4-[[5-trifluoromethyl)-2-pyridinyl] oxy] phenoxy] pentanoic acid} at 0.28 kg ai/ha controlled ‘Tifway’ bermudagrass [Cynodon transvaalensis Burtt-Davy #3 CYNTR] x [Cynodon dactylon (L.) Pers. # CYNDA] nearly 100% when applied for 2 consecutive years. Tall fescue (Festuca arundinacea Schreb. ‘Ky 31’ # FESAR) tolerated fluazifop at 0.13 kg/ha and SC-1084 at 0.07 to 0.28 kg/ha; however, centipedegrass [Eremochloa ophiuroides (Munro) Hack, ‘common’ #ERLOP] and zoysiagrass (Zoysia japonica Steud. # ZOYJA x Zoysia tenuifolia Willd. ex trin. ‘Emerald’ #ZOYTE did not tolerate these treatments. Centipedegrass tolerated sethoxydim, zoysiagrass tolerance was intermediate, and tall fescue was injured severely. Sethoxydim at 0.22 kg/ha discolored leaves of zoysiagrass, but the turf recovered fully. Thus, bermudagrass, when mixed with either tall fescue, centipedegrass, or zoysiagrass, can be controlled selectively with herbicides applied postemergence.

Field experiments were conducted from 1983 through 1987 to evaluate various postemergence grass herbicides on bermudagrass in peanuts. Fluazifop, haloxyfop, and SC-1084 applied once effectively controlled common bermudagrass when less than 8 cm tall, but resulted in variable control when applied to bermudagrass 15 cm or taller. Sethoxydim effectively controlled common bermudagrass one of 2 yr. ‘Coastal’ bermudagrass required two applications of BAS 517, fluazifop-P at 0.21 or 0.28 kg ai/ha, and haloxyfop for control of better than 88%. Clethodim and sethoxydim provided poor to fair control, respectively.

Field experiments were conducted during 1982 to 1988 in Virginia to evaluate BAS 517, CGA 82725, clethodim, cloproxydim, fenoxaprop, fluazifop, fluazifop-P, haloxyfop, paraquat, quizalofop, SC-1084, sethoxydim, sethoxydim plus thifensulfuron, and terbacil for control of annual grasses in alfalfa. Herbicides were applied to alfalfa and grasses 2 to 30 cm in height after the first and/or second cuttings. Overall, the herbicides were highly effective in controlling fall panicum, giant foxtail, barnyardgrass, and large crabgrass. Alfalfa yields were not increased with herbicide treatments in several experiments. Only paraquat, applied later than recommended after cutting in one experiment, and sethoxydim plus thifensulfuron at one location reduced alfalfa yields.