Rigid ryegrass is a problematic weed species in winter crops and winter fallow; however, recently, this weed species has been observed in summer crops and fallow. These observations warrant the evaluation of different postemergence herbicides for its control. Outdoor pot studies were conducted during the spring and summer of 2021 to 2022 to determine the performance of POST herbicides on two summer-emerging (S3 and S6) and two winter-emerging (W3 and W8) accessions of rigid ryegrass. Across all accessions, butroxydim, clethodim, paraquat, and paraquat + amitrole at the field rate provided complete control of rigid ryegrass. Both summer-emerging accessions were found to be resistant to the field rates of glufosinate (750 g ai ha−1), glyphosate (454 g ae ha−1), haloxyfop (52 g ai ha−1), and pinoxaden (30 g ai ha−1). The S6 accession had the highest dose required for a 50% reduction in biomass for these herbicides (glufosinate 1,120 g ai ha−1, glyphosate 1,210 g ae ha−1, haloxyfop 140 g ai ha−1, and pinoxaden 55 g ai ha−1). This summer-emerging accession (S6) was also resistant to iodosulfuron. All four accessions were found susceptible to imazamox + imazapyr (a commercial mixture) and mesosulfuron. The study provides the first evidence of poor control of summer-emerging accessions of rigid ryegrass with different herbicides. Multiple-herbicide-resistant summer-emerging rigid ryegrass accessions would be a challenge to the production of summer crops (e.g., cotton and sorghum) as well as winter crops that rely on weed-free summer fallows for soil moisture retention; therefore these accessions warrant diversified management strategies.

Control of glyphosate-resistant (GR) junglerice is a challenging task in eastern Australia. There is limited information on the efficacy and reliability of alternate herbicides for GR populations of junglerice, especially when targeting large plants and when temperatures are high. A series of experiments were conducted to confirm the level of glyphosate resistance in three populations of junglerice and to evaluate the efficacy of alternate herbicides for the control of GR junglerice populations. The LD50 of glyphosate of B17/7, B17/34, and B17/35 populations was found to be 298, 2,260, and 1,715 g ae ha–1, respectively, suggesting that populations B17/34 and B17/35 were highly resistant to glyphosate. Glyphosate efficacy was reduced at high-temperature (35 C day/25 C night) compared with low-temperature conditions (25 C day/15 C night), suggesting that control of susceptible populations may also be reduced if glyphosate is sprayed under hot conditions. Preemergence herbicides dimethenamid-P (1,000 g ai ha–1) and pendimethalin (1,500 g ai ha–1) provided 100% control of GR populations (B17/34 and 17/35). Postemergence herbicides, such as clethodim (60 or 90 g ai ha–1), glufosinate (750 g ai ha–1), haloxyfop (52 or 78 g ai ha–1), and paraquat (400 or 600 g ai ha–1), applied at the four-leaf stage provided 100% control of GR populations. For larger junglerice plants (eight-leaf stage), postemergence applications of paraquat (400 or 600 g ai ha–1) provided greater weed control than clethodim, glufosinate, and haloxyfop. A mixture of either glufosinate or haloxyfop with glyphosate provided poor control of GR junglerice populations compared with application of glufosinate or haloxyfop applied alone. Efficacy of glufosinate and haloxyfop for the control of GR populations decreased when applied in the sequential spray after glyphosate application. This study identified alternative herbicide options for GR junglerice populations that can be used in herbicide rotation programs for sustainable weed management.

Proso millet (Panicum miliaceum L. # PANMI) was controlled in corn (Zea mays L. ‘Pioneer 3747’) with postemergence-directed herbicides applied following a standard preplant-incorporated application of butylate [S-ethylbis(2-methylpropyl)carbamothioate] plus dichlormid (2,2-dichloro-N,N-di-2-propenylacetamide) plus cyanazine {2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl]amino]-2-methylpropanenitrile}. Postemergence-directed applications of ametryn [N-ethyl-N′-(1-methylethyl)-6-(methylthio)-1,3,5-triazine-2,4-diamine], cloproxydim {(E,E)-2-[1-[[(3-chloro-2-propenyl)oxy]imino]butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one}, butyl ester of fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy] propanoic acid}, butyl ester of fluazifop-p {(R)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy] propanoic acid}, glyphosate [N-(phosphonomethyl)glycine], methyl ester of haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy]propanoic acid}, and sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} in 40-cm-tall corn gave greater than 90% control of 5- to 15-cm-tall proso millet while causing little or no corn injury at selected rates. Season-long proso millet control was obtained with sethoxydim at rates as low as 56 g ai/ha with no visible corn injury. Unacceptable injury to 40-cm-tall corn occurred with all but the lowest rate of sethoxydim (56 g ai/ha) when a crop oil concentrate was used. Sethoxydim applied as a directed spray at rates up to 110 g ai/ha plus 1.25% (v/v) crop oil concentrate did not injure 60-cm-tall corn.

Field research was conducted in 1988 and 1989 to compare effects of clethodim, fenoxaprop, haloxyfop, and sethoxydim each applied singly and sequentially at full (1X) and reduced (0.5X) rates on barnyardgrass, bearded sprangletop, and rice. A tank-mixture of propanil plus thiobencarb (2.2 + 2.2 kg ha–1) applied sequentially was included as a standard treatment. Control of barnyardgrass and bearded sprangletop was equal to that of the standard treatment both years with 1X rates of clethodim and fenoxaprop, and with 0.5X rates of clethodim, fenoxaprop, and sethoxydim each applied after propanil; rice so treated produced high grain yields. In 1988, severe rice injury occurred after the second application of clethodim at the 0.5X rate, but rice recovered. Grass control costs were reduced 57% with a single application of fenoxaprop at the 1X rate compared with the standard treatment, but net returns were not different.

When tank mixed with certain boadleaf-selective herbicides, fluazifop {(+)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid}, sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one}, haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid}, and fluazifop-P {(R)-2-[4-[[5-trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} were less effective in controlling two annual grasses, Texas panicum (Panicum texanum Buckl. #3 PANTE) and large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA]. These herbicides were applied alone or were combined with the broadleaf-selective herbicides bentazon {3-(1-methylethyl)-(1H)-2,l,3-benzothiadiazin-4(3H)-one-2,2-dioxide} and/or 2,4-DB [4-(2,4-dichlorophenoxy)butanoic acid]. The herbicide combinations controlled smooth pigweed (Amaranthus hybridus L. # AMACH) and yellow nutsedge (Cyperus esculentus L. #CYPES). Increasing the rates of the grass-selective herbicides in the mixture reduced the adverse effects of 2,4-DB or bentazon.

Common bermudagrass [Cynodon dactylon (L.) Pers. #3 CYNDA] and johnsongrass [Sorghum halepense (L.) Pers. # SORHA] ecotypes were collected from seven locations in Texas. Ecotype responses to glyphosate [N-(phosphonomethyl)glycine], SC-0224 (trimethylsulfonium carboxymethylaminomethylphosphonate), sethoxydim {2-[l-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one}, fluazifop {(+)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid}, haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid}, and quizalofop {(+)-2-[4-[(6-chloro-2-quinoxalinyl)oxy] phenoxy] propanoic acid} were evaluated in 1982, 1983, and 1984. Johnsongrass ecotype-by-herbicide interactions and ecotype differences were detected in only one of three years. Differences were observed consistently among the herbicide treatments. Numerous bermudagrass ecotype-by-herbicide interactions were detected each year with greater diversity occurring with less-than-optimum herbicide rates. The interactions were herbicide-by-ecotype specific and were not predictable with respect to geographic site of collection.

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.

Quizalofop controlled 2- to 3-leaf and 5- to 6-leaf red rice better than fluazifop-P, haloxyfop, or sethoxydim applied alone. Red rice control increased when acifluorfen was tank mixed with haloxyfop, fluazifop-P, or sethoxydim. Antagonism was most severe when imazaquin was tank mixed with any of the grass herbicides. The efficacy of sethoxydim, fluazifop-P, and haloxyfop was reduced when applied with chlorimuron or bentazon. In greenhouse experiments, all of the grass herbicides, except for fenoxaprop, reduced fresh weight of red rice 71% or more. Based on fresh weight reduction, acifluorfen, fomesafen, and lactofen only reduced the activity of fluazifop-P, while imazaquin decreased the activity of all grass herbicides.

Between 1982 and 1986, spring treatments of haloxyfop, fluazifop, and sethoxydim all applied at 400 g ai/ha alone and combined with dalapon at 3400 g ai/ha were evaluated for quackgrass control and subsequent effect on established birdsfoot trefoil seed production. Haloxyfop alone and combined with dalapon were superior to fluazifop or sethoxydim alone or mixed with dalapon for controlling quackgrass and other grass weeds. Birdsfoot trefoil seed yield averages over 3 yr were 310, 160, 150, and 180 kg/ha after treatment with haloxyfop, fluazifop, sethoxydim, and dalapon, respectively, compared to a control yield of 80 kg/ha. Yields were lower, 220 kg/ha, with combinations involving haloxyfop plus dalapon compared to haloxyfop alone.

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.

The successful introduction of a new crop depends upon the availability of economical, safe, and effective herbicides for that crop. Greenhouse trials identified PRE herbicide applications of 4.5 kg ai ha−1 of metolachlor and of alachlor, 2.2 kg ai ha−1 of linuron and of pendimethalin, and 1.1 kg ai ha−1 of desmediphan as noninjurious to sweet white lupin. POST applications of 0.28 kg ai ha−1 of sethoxydim and of fluazifop and 0.22 kg ai ha−1 of haloxyfop also did not injure the sweet white lupin. Field trials indicated that safe and effective weed control could be obtained with combinations of linuron with metolachlor, alachlor, or pendimethalin depending on weed species present.

In laboratory and field studies, quackgrass (Agropyron repens (L.) Beauv. # AGRRE) was subjected to postemergence applications of the butyl ester of fluazifop-P {(R)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid}, methyl ester of haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid}, or ethyl ester of quizalofop {2-[4-[[6-(chloro-2-quinoxalinyl)oxy] phenoxy] propanoic acid}. Haloxyfop, fluazifop-P, and quizalofop each required a minimum of 1 week to reduce quackgrass transpiration or water uptake in the laboratory. At rates lower than 0.56 kg ae/ha, fluazifop-P reduced quackgrass transpiration and water usage less quickly and to a lesser extent than equivalent rates of haloxyfop and quizalofop. The time required for significant transpiration and water uptake reduction by herbicide-treated quackgrass was several days longer in the field than in the laboratory, but the reaction patterns among the herbicides were similar. Little if any benefit was obtained from sequential applications of the herbicides compared with single applications of the same total dosage. All three herbicides significantly reduced quackgrass dry weight.

Preplant incorporation of alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] at 3.6 kg ai/ha, metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] at 2.2 kg ai/ha, and tank mixtures of imazaquin {2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid} with either alachlor at 0.14 + 2.2 kg ai/ha or metolachlor at 0.14 + 1.1 kg ai/ha controlled >90% red rice (Oryza sativa L. # ORYSA) in soybeans [Glycine max (L.) Merr.]. Also, FMC-57020 [2-(2-chlorophenyl)methyl-4,4-dimethyl-3-isoxazolidinone] at 1.7 kg ai/ha applied preplant incorporated controlled > 80% of the red rice. DPX-Y6202 {2-[4-[(6-chloro-2-quinoxalinyl)oxy]-phenoxy]-propionic acid, ethyl ester} was the best and most consistent postemergence herbicide treatment for red rice control when applied once at 0.28 kg ai/ha or sequentially at 0.14 kg ai/ha each time. Haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl]oxy] phenoxy] propanoic acid} applied at 0.16 kg ai/ha followed by another application at 0.14 kg ai/ha gave excellent red rice control in 2 of 3 years. Soybeans were uninjured by the herbicide treatments and yield was higher from treated than untreated soybeans.

Two field experiments were conducted in 1984 and 1985 to determine the effects of fluazifop, haloxyfop, and sethoxydim on the suppression of water uptake and competition of wheat to seedling alfalfa. In all cases, suppression of wheat growth and stand led to significant reduction in soil water use. The amounts of conserved soil water significantly correlated with increased numbers of alfalfa plants; the correlation coefficients, respectively, for mid- and late-summer plantings were 0.47 and 0.41 in 1984 and 0.90 and 0.86 in 1985. Conservation of soil water was attributed to growth reduction or cessation of wheat growth by the herbicides and, to some extent, suppression of wheat leaf transpiration. All of the three herbicides would be effective in controlling volunteer wheat in a new alfalfa planting.

Control of seedling and rhizome johnsongrass [Sorghum halepense (L.) Pers. # SORHA] with five herbicides was evaluated after postemergence application in various diluents and spray volumes using one to three types of applicators from 1983 to 1985. The rate of each herbicide required to control seedling johnsongrass using paraffinic oil as the diluent in applications with an external- or internal-mixing air-assist sprayer at a spray volume of 9.4 L/ha was one-half the rate required when water plus 1.25% (v/v) paraffinic oil concentrate (POC) or water plus 1.25% (v/v) soybean oil concentrate (SOC) were the diluents in applications with a conventional sprayer equipped with fan jet spray nozzles at a spray volume of 187 L/ha. Rates were also reduced when once-refined soybean oil was the diluent at a spray volume of 9.4 L/ha, except for the ethyl ester of quizalofop {(±)-2-[4-[(6-chloro-2-quinoxalinyl)oxy] phenoxy] propanoic acid}. Sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} was equally effective on seedling johnsongrass growing in soybeans [Glycine max (L.) Merr. ‘DPL 105’] when applied at 224 g ai/ha with an internal-mixing air-assist sprayer or a controlled-droplet applicator (CDA) at a spray volume of 9.4 L/ha and a conventional sprayer at a spray volume of 187 L/ha, regardless of diluent. Conventional application required the use of 1.25% (v/v) SOC or POC as part of the diluent to be effective. For three of the five herbicides evaluated on rhizome johnsongrass, paraffinic oil at a spray volume of 9.4 L/ha was the only diluent that resulted in season-long control. Rhizome johnsongrass control with this diluent also resulted in significantly higher soybean yields than all other diluent-spray volume treatments.

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.

Field studies were conducted in 1987 and 1988 at Fayetteville and Clarkedale, AR, to evaluate various herbicide treatments for johnsongrass control in soybeans. Herbicide treatments were postemergence applications of sethoxydim, fenoxaprop, fluazifop-P, haloxyfop, quizalofop, imazethapyr, and clethodim. No significant soybean injury was noted in 1987 or 1988 at either location in the johnsongrass experiments. All treatments except those with fenoxaprop and imazethapyr, provided 70 to 90% johnsongrass control. Generally, soybean yields were reduced from treatments that controlled less than 60% of the johnsongrass.

Both alachlor at 3.6 kg ai/ha and metolachlor at 2.8 kg ai/ha applied preplant incorporated consistently controlled red rice 82% and 90%, respectively, over a 3-yr period. Averaged across years, only mefluidide at 0.14 kg ai/ha plus bentazon at 0.84 kg ai/ha, haloxyfop at 0.28 kg ai/ha, and quizalofop at 0.14 kg ai/ha applied postemergence controlled red rice comparable to the preplant herbicide treatments. High rates of sethoxydim and fluazifop (0.56 kg ai/ha), haloxyfop (0.28 kg ai/ha), and quizalofop (0.14 kg ai/ha) were needed to obtain soybean yields equivalent to alachlor and metolachlor.

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.