Genetic similarities between johnsongrass and grain sorghum leave producers with limited herbicide options for postemergence johnsongrass control. TamArkTM grain sorghum with resistance to acetyl-CoA carboxylase-inhibiting herbicides was developed through a collaboration between the University of Arkansas System Division of Agriculture and Texas A&M AgriLife Research. Two field experiments were conducted in 2021 in two locations each: Keiser and Marianna, AR, or Fayetteville and Marianna, AR. The objective of the first was to determine the optimal rate and application timing of fluazifop-butyl for control of natural johnsongrass populations in a noncrop setting, and the objective of the second was to evaluate johnsongrass control and TamArkTM grain sorghum tolerance in response to fluazifop-butyl applied at different timings and rates based on crop growth stage. The highest levels of johnsongrass control occurred when sequential applications of fluazifop-butyl were utilized. All sequential treatments provided at least 80% johnsongrass control at any rate or application timing tested. A single application of fluazifop-butyl provided greater than 90% johnsongrass control when applied at 210 g ai ha−1 to johnsongrass with fewer than 6 leaves. Weed size played a role in achieving high levels of johnsongrass control. Greater than 90% control was achieved when johnsongrass had 6 leaves or fewer at the initial application for the sequential application treatments. A single application of fluazifop-butyl at 105 g ai ha−1 resulted in no more than 82% johnsongrass mortality at any application timing. TamArk™ grain sorghum injury did not exceed 6% at any application timing or rate. It was therefore considered to be safe even if the initial application was made before the 6-leaf crop stage. Because no unacceptable levels of injury were observed with TamArk™ grain sorghum for fluazifop-butyl, johnsongrass size at the time of application should be the most critical aspect for control with this herbicide.

Seedling alfalfa was injured by chlorsulfuron and sethoxydim plus 2,4-DB but recovered the following year as alfalfa seed yields were comparable to the hand-weeded control. Fluazifopbutyl and flamprop-methyl (active isomer) at 0.5 kg/ha did not affect seedling alfalfa adversely; however, seed yields were lower the following year compared to those treated at the 0.25-kg/ha rate. In established alfalfa, sethoxydim alone or with 2,4-DB applied annually did not affect seed yields adversely. However, 2,4-DB alone reduced seed yields in 2 of 5 yr. Alfalfa tolerated chlorsulfuron at 0.015 kg/ha but was damaged at the 0.03-kg/ha rate. Initial injury and later recovery without adverse effects on seed yield also were observed following annual treatments with bromoxynil, MCPA plus 2,4-DB and bentazon plus 2,4-DB.

The current emphasis on reducing pesticide use has led to increased interest in alternative weed control methods. The purpose of this study was to evaluate the potential of hilling, in combination with subsequent interseeding of cover crops, to control weeds in potato and to determine the impact of these actions on potato yield and insects. Each cover crop, either hairy or lana vetch, oats, barley, red clover, or a combination of oats and hairy vetch, was interseeded, following hilling, 3, 4, or 5 wk after planting (WAP). Hilling and interseeding treatments were compared to a no-cover treatment and a chemical standard, metolachlor (1.7 kg ai ha−-1) plus linuron (1.7 kg ai ha−-1). Cultivation associated with the interseeding operation and cover crops reduced weed density 20 to 27% by 3 wk after interseeding. To prevent excessive competition, cereals interseeded 3 or 4 WAP and vetches interseeded 3 WAP were controlled at a height of 25 to 35 cm using fluazifop (0.22 kg ai ha−-1) plus metribuzin (0.28 kg ai ha−-1). Because of slow growth, it was necessary to control red clover (interseeded 3 WAP), only in 1996, at a height of 15 cm. Control of cereals resulted in a dead mulch that provided 0 to 95% weed control, whereas legumes regrew after herbicide application and provided 45 to 70% weed control. However, an adequate minimum of 70% weed control was achieved only with the chemical standard, cereals (1995 and 1996), and legumes (1996) interseeded 3 WAP when controlled with herbicides. In a dry season (1995), potato yields were highest with the chemical standard, whereas in a season with adequate precipitation (1996), potato yields equivalent to those of the chemical standard were obtained with early interseeding (3 WAP) of cereals. The observed changes in the densities of potato leafhopper and of its natural enemies were unlikely to have any effect on potato yield because of low overall insect populations. Thus, the results suggest that in good growing conditions, early (3 WAP) interseeding of cover crops supplemented with postemergence herbicides may both suppress weeds with 70% less herbicide (ai ha−-1) and provide yields comparable to those associated with conventional potato production.

Several field studies were conducted during 1981 and 1982 to determine whether early preplant (EPP) applications of residual herbicides would prevent the establishment of vegetation before planting no-till soybeans [Glycine max (L.) Merr. ‘Williams’]. Early preplant applications of either cyanazine {2-[[4-chloro-6-(ethylamino)-s-triazin-2-yl] amino]-2-methylpropionitrile} or cyanazine plus oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide) were applied in the fall and 3, 2, and 1 month(s) before planting no-till soybeans. In all studies, the treatments prevented vegetation from becoming established before planting, and season-long weed control was achieved with several different treatments. Early preplant cyanazine plus oryzalin provided greater than 90% control for the entire season where grass densities were low. Where grass densities were high (greater than 90% ground cover), EPP cyanazine plus a preemergence application of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] plus metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] or a postemergence application of sethoxydim {2-[1-(ethoxyimino) butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} controlled 90% of the weeds, which was equal to or better than the standard preemergence treatments used (80 to 98% weed control).

Under greenhouse conditions, approximately 50% visible control of bermudagrass [Cynodon dactylon (L.) Pers. ♯3 CYNDA], quackgrass [Agropyron repens (L.) Beauv. ♯ AGRRE], and wirestem muhly (Muhlenbergia frondosa L. ♯ MUHFR) was obtained using 0.56 kg/ha glyphosate [N-(phosphonomethyl)glycine], CGA-82725 {2-propynyl-2-[4-([3,5-dichloro-2-pyridinyl] oxy) oxy)phenoxy propanoate}, 0.28 kg/ha fluazifop-butyl {(±)-butyl 2-[4-[(5-(trifluoromethyl)-2-pyridinyl)oxy] phenoxy] propanoate}, sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one}, and 0.11 kg/ha haloxyfop-methyl [methyl 2-(4-((3-chloro-5-(trifluoromethyl)-2-pyridinyl)oxy)phenoxy)propanoate]. Except for quackgrass, sethoxydim and fluazifop-butyl reduced shoot regrowth in plants clipped 3 to 6 h after treatment Sethoxydim required a 24-h duration on quackgrass foliage to reduce growth. Fresh weights of haloxyfop-methyl- and CGA-82725-treated plants required a 12- to 24-h clipping for reduced regrowth in all species. For all herbicides and species tested, little or no regrowth occurred when plants were clipped 48 h after treatment. A 1-h interval between split applications of sethoxydim and a 24-h interval between split applications of fluazifop-butyl and haloxyfop-methyl reduced fresh weights of bermudagrass regrowth when compared to an equivalent single rate. Regrowth of treated quackgrass indicated a 24-h interval was required for reductions with split applications of sethoxydim, fluazifop-butyl, and haloxyfop-methyl. Wirestem muhly regrowth was reduced after a 1-h interval between applications. In all species, superior control was obtained using two half-rate applications compared to one full-rate application.

Greenhouse studies were initiated to determine the efficacy of four herbicide antidotes as protectants of corn (Zea mays L., ‘DeKalb XL72AA’ and ‘DeKalb XL67′) against injury from preemergence or early postemergence applications of the herbicides chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide}, fluazifop-butyl {butyl-2-[4-[5-(trifluoromethyl-2-pyridinyl)oxy] phenoxy] propanoate}, or BAS 9052 OH {2-[1-(ethoxyimino)-butyl]-5-[2-(ethylthio)-propyl]-3-hydroxy-2-cyclohexene-1-one}. NA (1,8-naphthalic anhydride) was the most effective of the four antidotes in protecting corn against injury from preemergence applications of chlorsulfuron. CGA-43089 [α-(cyanomethoxy)-imino-benzeneacetonitrile] and CGA-92194 [α-(1,3-dioxolan-2-yl-methoxy)-imino-benzeneacetonitrile] partially protected corn from chlorsulfuron injury, whereas R-25788 (N,N-diallyl-2,2-dichloroacetamide] was the least effective. R-25788 offered partial to good protection to corn against injury from preemergence applications of fluazifop-butyl and BAS 9052 OH. NA, or CGA-43089, and CGA-92194 partially protected corn from fluazifop-butyl injury but their efficacy against BAS 9052 OH injury to corn was limited. In general, all four antidotes offered better protection to the thiocarbamate-tolerant ‘XL72AA’ hybrid than to the thiocarbamate-susceptible ‘XL67’ hybrid. With the exception of NA, which partially protected corn from postemergence-applied chlorsulfuron, none of the four herbicide antidotes was effective in protecting corn against injury from postemergence applications of any of the three herbicides.