Patrick W. Geier

Dose Responses of Five Broadleaf Weeds to Saflufenacil

Abstract Greenhouse dose–response studies were conducted to determine the effectiveness of PRE and POST applications of saflufenacil on blue mustard, flixweed, Palmer amaranth, redroot pigweed, and tumble pigweed. Weed species did not differ in their responses to saflufenacil applied PRE. Averaged across species, PRE application of saflufenacil at 6 to 30 g/ha reduced weed biomass 82 to 98%, but biomass did not differ among rates of 12 g/ha or higher. POST application of saflufenacil reduced weed biomass by 92%, averaged across species and rates. On the basis of regression analysis, the 90% plant biomass reduction for saflufenacil applied PRE and POST was 9 and 6 g/ha, respectively. Saflufenacil applied PRE reduced population density by 77 to 98%, averaged across weed species; a rate of 9 g/ha reduced population density 90% (DR90) on the basis of regression analysis. Averaged across species, POST application of 6 to 30 g/ha reduced population density by 63 to 93%, but regression analysis indicated that the DR90 value was greater than 30 g/ha. Averaged across rates, saflufenacil reduced the population density of flixweed, Palmer amaranth, redroot pigweed, tumble pigweed, and blue mustard by 49, 64, 67, 73, and 78%, respectively. Nomenclature: Saflufenacil, N′-[2-chloro-4-fluoro-5-(3-methyl-2,6-dioxo-4-(trifluoromethyl)-3,6-dihydro-1(2H)pyrimidinyl)benzoyl]-N-isopropyl-N-methylsulfamide; blue mustard, Chorispora tenella (Pallas) DC., COBTE; flixweed, Descurainia sophia (L.) Webb. ex Prantl, DESSO; Palmer amaranth, Amaranthus palmeri S.Wats., AMAPA; redroot pigweed, Amaranthus retroflexus L., AMARE; tumble pigweed, Amaranthus albus L., AMAAL.

KIH-485 and S-metolachlor efficacy comparisons in conventional and no-tillage corn

Field experiments were conducted during 2003 and 2004 to compare the effectiveness of KIH-485 and S-metolachlor for PRE weed control in no-tillage and conventional-tillage corn. Longspine sandbur control increased as KIH-485 or S-metolachlor rates increased in conventional-tillage corn, but control did not exceed 75% when averaged over experiments. Both herbicides controlled at least 87% of green foxtail with the exception of no-tillage corn in 2004, when KIH-485 was more effective than S-metolachlor at lower rates. Palmer amaranth control ranged from 85 to 100% in 2003 and 80 to 100% in 2004, with the exception of only 57 to 76% control at the lowest two S-metolachlor rates in 2004. Puncturevine control exceeded 94% with all treatments in 2003. In 2004, KIH-485 controlled 86 to 96% of the puncturevine, whereas S-metolachlor controlled only 70 to 81%. Mixtures of atrazine with KIH-485 or S-metolachlor generally provided the most effective control of broadleaf weeds studied. Nomenclature: Atrazine; KIH-485; S-metolachlor; Palmer amaranth, Amaranthus palmeri S. Wats. #3 AMAPA; green foxtail, Setaria viridis (L.) Beauv. # SETVI; puncturevine, Tribulus terrestris L. # TRBTE; longspine sandbur, Cenchrus longispinus (Hack.) Fern. # CCHPA; corn, Zea mays L. Additional index words: Tillage systems, best management practices. Abbreviations: BMP, best management practices; DAT, days after herbicide treatment; Kow, herbicide adsorption coefficient.

Grain Sorghum Response to Simulated Drift from Glufosinate, Glyphosate, Imazethapyr, and Sethoxydim1

Field experiments were conducted at four locations in Kansas in 1999 and 2000 to evaluate grain sorghum response to simulated drift rates of four herbicides. Imazethapyr, glufosinate, glyphosate, and sethoxydim were applied at 1/3, 1/10, 1/33, and 1/100 of the use rate when plants were 10 to 20 cm tall. Visible crop injury increased as rates of each herbicide increased. Glyphosate and imazethapyr caused the most injury and glufosinate the least. Data show that some plants that were significantly injured 2 wk after treatment (WAT) recovered 8 WAT. However, some plants that received the highest rate of imazethapyr or glyphosate died. Grain sorghum yields were reduced only when injury was severe. This research showed that the potential for sorghum injury from off-target herbicide drift is greater from imazethapyr and glyphosate than from sethoxydim or glufosinate. Nomenclature: Glufosinate; glyphosate; imazethapyr; sethoxydim; sorghum, Sorghum bicolor (L.) Moench. Additional index words: Crop injury, herbicide drift, herbicide symptoms. Abbreviations: DAT, days after treatment; WAT, weeks after treatment.

Imazamox for Winter Annual Grass Control in Imidazolinone-Tolerant Winter Wheat

Field experiments were conducted at five locations in Kansas, Nebraska, and Wyoming to determine the effects of imazamox rate and application timing on winter annual grass control and crop response in imidazolinone-tolerant winter wheat. Imazamox at 35, 44, or 53 g ai/ha applied early-fall postemergence (EFP), late-fall postemergence, early-spring postemergence (ESP), or late-spring postemergence (LSP) controlled jointed goatgrass at least 95% in all experiments. Feral rye control with imazamox was 95 to 99%, regardless of rate or application timing at Hays, KS, in 2001. Feral rye control at Sidney, NE, and Torrington, WY, was highest (78 to 85%) with imazamox at 44 or 53 g/ha. At Sidney and Torrington, feral rye control was greatest when imazamox was applied EFP. Imazamox stunted wheat <10% in two experiments at Torrington, but EFP or LSP herbicide treatments in the Sidney experiment and ESP or LSP treatments in two Hays experiments caused moderate (12 to 34%) wheat injury. Wheat injury increased as imazamox rate increased. Wheat receiving imazamox LSP yielded less grain than wheat treated at other application timings in each Hays experiment and at Sidney in 2001. No yield differences occurred in one Torrington experiment. However, yields generally decreased as imazamox application timing was delayed in the other Torrington experiment. Generally, imazamox applied in the fall provided the greatest weed control, caused the least wheat injury, and maximized wheat yield. Nomenclature: Imazamox; feral rye, Secale cereale L. #3 SECCE; jointed goatgrass, Aegilops cylindrica Host # AEGCY; wheat, Triticum aestivum L. ‘CO980875’. Additional index words: Central Great Plains, herbicide-tolerant wheat, IMI-wheat. Abbreviations: EFP, early-fall postemergence; ESP, early-spring postemergence; KS-A, Hays, KS, experiment A; KS-B, Hays, KS, experiment B; LFP, late-fall postemergence; LSP, late-spring postemergence; MSO, methylated seed oil; NE, Sidney, NE; UAN, urea ammonium nitrate; WY-A, Torrington, WY, experiment A; WY-B, Torrington, WY, experiment B.

Winter Wheat and Weed Response to Postemergence Saflufenacil Alone and in Mixtures

Abstract Growth chamber experiments were conducted in the fall of 2006 and spring of 2007 to determine winter wheat, flixweed, and henbit response to POST treatments of saflufenacil at 13, 25, and 50 g ai ha−1 applied alone and in combinations with bentazon at 560 g ai ha−1 or 2,4-D amine at 533 g ae ha−1 and nonionic surfactant (NIS) at 0.25% v/v. Mixtures of saflufenacil and 2,4-D amine were also applied without NIS. Necrosis was observed on wheat leaves within 1 d after treatment (DAT) and peaked at 5 to 7 DAT. Saflufenacil at 13, 25, or 50 g ai ha−1 applied alone or in combination with 533 g ae ha−1 of 2,4-D amine plus NIS caused 19 to 38% (alone) and 24 to 40% (in combination) wheat foliar necrosis, respectively. Foliar necrosis of wheat was 14% or less when saflufenacil, at any rate, was mixed with bentazon or 2,4-D amine without NIS. Combinations of saflufenacil at any of the rates tested plus bentazon and NIS did not reduce wheat dry weight. Saflufenacil plus 2,4-D amine without adjuvant resulted in similar wheat dry weights as 2,4-D amine. Saflufenacil plus 2,4-D amine without NIS provided 99% control of flixweed at 21 DAT, but henbit control ranged from 81 to 88%. In comparison, saflufenacil at 50 g ha−1 mixed with bentazon and NIS controlled flixweed at 92% and henbit at 63% at 21 DAT. This research indicates saflufenacil has potential for POST use in winter wheat to control winter annual broadleaf weeds when tank-mixed with 2,4-D amine without NIS, but additional research is needed to discover ways to improve crop safety without reducing weed control. Nomenclature: 2,4-D amine; bentazon; saflufenacil; flixweed, Descurainia sophia L. Webb. ex Prantl DESSO; henbit, Lamium amplexicaule L. LAMAM; winter wheat, Triticum aestivum L. ‘KS03HW6-1’.

Differential Response of Grain Sorghum Hybrids to Foliar-Applied Mesotrione

Abstract The selection of herbicide-resistant weeds in grain sorghum production has prompted researchers to explore alternative herbicides to prevent, delay, and manage herbicide-resistant weed biotypes. Greenhouse and field experiments were conducted to evaluate the differential response of sorghum hybrids to POST application of mesotrione. In a greenhouse experiment, 85 sorghum hybrids were treated with 0, 52, 105, 210, and 315 g ai/ha mesotrione when plants were at the three- to four-leaf collar stage. Sorghum response ranged from susceptible to tolerant sorghum hybrids. ‘Pioneer 84G62’, ‘Pioneer 85G01’, and ‘Triumph TR 438’ were the three most susceptible, whereas ‘Dekalb DKS35-70’, ‘Frontier F222E’, and ‘Asgrow Seneca’ were the three most tolerant hybrids. One week after treatment (WAT), the mesotrione rate causing 50% visible injury ranged from 121 to 184 and 64 to 91 g/ha in the most tolerant and susceptible hybrids, respectively. Mesotrione dose–response studies were conducted under field conditions on four sorghum hybrids. One WAT, injury symptoms were greater (up to 23%) in Pioneer 85G01 than in Asgrow Seneca (< 14%). However, all plants appeared normal by the end of the growing season. In addition, sorghum yields were not reduced by mesotrione treatments as verified by correlation coefficient analysis. Nomenclature: Mesotrione; sorghum, Sorghum bicolor (L.) Moench. SORBI

Preemergence Herbicide Efficacy and Phytotoxicity in Grain Sorghum

Abstract Field studies conducted from 2005 to 2007 in Kansas compared the effects of KIH-485 and flufenacet to acetochlor and s-metolachlor applied PRE in grain sorghum. All treatments were combined with 1.12 kg/ha of atrazine for broadleaf weed control. KIH-485 and flufenacet, each at one time (1×) and two times (2×) the labeled rates, controlled large crabgrass 55 to 76% in 2005 and 94% or more in 2006 and 2007. In 2005, all herbicides controlled shattercane less than 20%, and only KIH-485 at the 2× rate controlled shattercane more than 70% in 2006 and 2007. Averaged over herbicides, green foxtail was controlled 98% in 2005, 77% in 2006, and 79% in 2007. Most herbicides controlled foxtail 86% or more when averaged over experiments, however, s-metolachlor at 1×, flufenacet at either rate, or atrazine alone did not. Sorghum was not stunted with KIH-485 or flufenacet in two of seven experiments. However, sorghum growth was reduced 23 to 54% with the 2× rates of KIH-485, flufenacet, or acetochlor in four experiments. Compared to the weed free control, sorghum stand establishment was reduced 18% with the 2× rate of flufenacet at Colby in 2006. At Hays in 2005, stand reductions occurred with acetochlor or KIH-485 at the 2× rates and either rate of flufenacet. Averaged over experiments, grain yields were reduced 9 and 10% with KIH-485 and flufenacet at the 2× rates, respectively. Where precipitation was greatest during the 2 wk following herbicide application, weed control was the best with these herbicides, but sorghum injury was also greatest. Nomenclature: Acetochlor; atrazine; flufenacet; KIH-485, 3-[(5-difluoromethoxy-1-methyl-3-trifluoromethylpyrazol-4-yl)methylsulfonyl]-4,5-dihydro-5,5-dimethylisoxazole; s-metolachlor; green foxtail, Setaria viridis (L.) Beauv. SETVI; large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA; shattercane, Sorghum bicolor (L.) Moench SORVU; grain sorghum, Sorghum bicolor (L.) Moench.

Winter Annual Broadleaf Weeds and Winter Wheat Response to Postemergence Application of Two Saflufenacil Formulations

Abstract Field experiments in winter wheat were initiated at two locations in the fall of 2006 and 2007 to evaluate winter annual broadleaf weeds and winter wheat response to POST applications of two saflufenacil formulations applied alone and in combination with 2,4-D amine. Emulsifiable concentrate (EC) and water-dispersible granule (WG) formulations of saflufenacil at 13, 25, and 50 g ai ha−1 were applied with 1.0% (v/v) crop oil concentrate (COC) and mixed with 2,4-D amine at 533 g ae ha−1 without adjuvant. Regardless of rate or formulation, saflufenacil plus COC and saflufenacil plus 2,4-D amine controlled blue mustard ≥ 91% at 17 to 20 d after treatment (DAT) compared with ≤ 50% control with 2,4-D amine alone. At least 25 g ha−1 of saflufenacil EC was necessary to control flixweed > 90%. Excluding COC from saflufenacil plus 2,4-D amine reduced flixweed control from the saflufenacil WG formulation more than the EC formulation. Most saflufenacil treatments did not control henbit satisfactorily (≤ 80%). Wheat foliar necrosis increased with increasing saflufenacil rate to as high as 30% at 3 to 6 DAT, but declined to < 15% at 10 to 20 DAT and was not evident at 30 DAT. Saflufenacil rate, formulation, and mixing with 2,4-D amine also influenced wheat stunting, but to a lesser extent than foliar necrosis. Saflufenacil EC consistently caused greater foliar necrosis and stunting on wheat than saflufenacil WG. Leaf necrosis and stunting were reduced by tank-mixing saflufenacil formulations with 2,4-D amine without COC. Grain yields of most saflufenacil treatments were similar to 2,4-D amine under weedy conditions and herbicide treatments had no effect on grain yield in weed-free experiments. Saflufenacil formulations at 25 to 50 g ha−1 with 2,4-D amine and saflufenacil WG at 25 to 50 g ha−1 with COC can control winter annual broadleaf weeds with minimal injury (< 15%) and no grain yield reductions. The addition of saflufenacil as a POST-applied herbicide would give wheat growers another useful tool to control annual broadleaf weeds, including herbicide-resistant weed species. Nomenclature: 2,4-Dichlorophenoxyacetic acid amine, 2,4-D amine; saflufenacil, N′-[2-chloro-4-fluoro-5-(3-methyl-2,6-dioxo-4-(trifluoromethyl)-3,6-dihydro-1(2H)-pyrimidinyl)benzyl]-N-isopropyl-N-methylsulfamide; blue mustard, Chorispora tenella (Pallas) DC. COBTE; flixweed, Descurainia sophia L. Webb. ex Prantl DESSO; henbit, Lamium amplexicaule L. LAMAM; winter wheat, Triticum aestivum L. ‘AP502-CL’, ‘Danby’, and ‘KS03HW6-1’.

Grain Sorghum (Sorghum bicolor) and Sunflower (Helianthus annuus) Response to MKH 6561 and MON 37500 Residues in Soil1

Field studies in 1998 and 1999 determined the response of grain sorghum and sunflower to soil residues of MKH 6561 and MON 37500 in a failed winter wheat recropping situation. Averaged across years, MON 37500 at 30 g ai/ha reduced sunflower density by 39%. MKH 6561 at 30 or 45 g/ha did not reduce sunflower density, growth, or late-season biomass, whereas MON 37500 reduced late-season biomass in both years. Neither herbicide affected grain sorghum plant density in 1998, but MON 37500 decreased sorghum density 80% in 1999. Sorghum growth, biomass, and yield were limited more severely by MON 37500 in 1999 than in 1998. MKH 6561 had little or no effect on grain sorghum during either year. Differences in crop response to MON 37500 between years was likely because of wheat plant size at the time of application and greater interception and metabolism of the herbicide in 1998 crop year. Nomenclature: MKH 6561, methyl 2-({[(4-methyl-5-oxo-3-propoxy-4,5-dihydro-1H-1,2,4-triazol-1-yl)carbonyl]amino}sulfonyl)benzoate sodium salt; MON 37500, 1-(4,6-dimethoxypyrimidin-2-yl)-3-(2-ethanesulfonyl-imidazo[1,2-a]pyridine-3-yl)sulfonylurea; grain sorghum, Sorghum bicolor (L.) Moench ‘Dekalb DK51’; sunflower, Helianthus annuus L. ‘Cargill SF187A’; winter wheat, Triticum aestivum. Additional index words: Herbicide carryover, emergency plant back, recrop, rotation. Abbreviations: POST, postemergence; PRE, preemergence.

Dose responses of weeds and winter wheat to MKH 6561

Abstract Greenhouse studies determined dose responses of winter annual weeds and winter wheat to preemergence (PRE) and postemergence (POST) treatments of MKH 6561 and the residual effects on kochia. MKH 6561 at 11 to 45 g ha−1 did not affect wheat. MKH 6561 at 11, 34, and 45 g ha−1 reduced winter annual weed densities compared to an untreated control. Weed growth was inhibited as the rate of MKH 6561 was increased, but downy brome, cheat, and Japanese brome were three to six times more susceptible than jointed goatgrass. The GR70 values for cheat, downy brome, Japanese brome, and jointed goatgrass were 7, 11, 4, and >45 g ha−1, respectively. Dry weights of kochia seeded after removal of the winter annual grasses decreased as MKH 6561 rate increased, with average control being 77% compared to the nontreated control. Regression analysis indicated that kochia was controlled 80% with MKH 6561 at 28 g ha−1. Nomenclature: MKH 6561, methyl 2-[[[(4-methyl-5-oxo-3-propoxy-4,5-dihydro-1H-1,2,4-triazol-1-yl)carbonyl]amino]sulfonyl]benzoate sodium salt; cheat, Bromus secalinus L. BROSE; downy brome, Bromus tectorum L. BROTE; Japanese brome, Bromus japonicus Thunb. ex Murr. BROJA; jointed goatgrass, Aegilops cylindrica Host AEGCY; kochia, Kochia scoparia Schrad. KCHSC; winter wheat, Triticum aestivum L. ‘2137’.