Douglas E. Shoup

Common waterhemp (Amaranthus rudis) resistance to protoporphyrinogen oxidase-inhibiting herbicides

Abstract Resistance to protoporphyrinogen oxidase (protox)-inhibiting herbicides was identified in a population of common waterhemp that had been treated with acifluorfen for several years. The protox-resistant biotype of common waterhemp was approximately 34, 82, 8, and 4 times more resistant than a susceptible common waterhemp biotype to acifluorfen, lactofen, fomesafen, and sulfentrazone, respectively. The resistant biotype also showed a high level of resistance to acetolactate synthase–inhibiting herbicides thifensulfuron and imazethapyr but not to glyphosate or paraquat. An organophosphate insecticide was applied with acifluorfen or lactofen to determine if metabolism could be the mechanism of resistance. No differences were observed between resistant plants treated with an organophosphate plus a protox-inhibiting herbicide and plants treated with a protox-inhibiting herbicide alone. Nomenclature: Acifluorfen-methyl; lactofen; fomesafen; sulfentrazone; thifensulfuron-methyl; imazethapyr; glyphosate; paraquat; malathion; diazinon; common waterhemp, Amaranthus rudis Sauer AMATA.

Protox-resistant common waterhemp (Amaranthus rudis) response to herbicides applied at different growth stages

Abstract Greenhouse and field studies were conducted with a population of common waterhemp resistant to POST protoporphyrinogen oxidase (protox)-inhibiting herbicides to compare its response to PRE and POST applications of selected herbicides. In the greenhouse, a dose–response study of PRE applications of acifluorfen, fomesafen, or lactofen was conducted on protox-susceptible and -resistant common waterhemp. The protox-resistant biotype was approximately 6.3, 2.5, and 2.6 times more resistant than the susceptible biotype to acifluorfen, fomesafen, and lactofen, respectively. In a separate study under field conditions, protox-resistant common waterhemp were treated with PRE and POST applications of acifluorfen, azafenidin, flumioxazin, fomesafen, lactofen, oxyfluorfen, or sulfentrazone. At 14 and 28 d after POST treatment (DAPT) in 2002 and 2004, all PRE applications of herbicides gave greater control than did POST applications. At 14 DAPT, oxyfluorfen had the greatest difference in PRE and POST control, with 85 and 10% control in 2002, respectively. An additional field study was conducted to determine the stage of growth at which resistance to protox-inhibiting herbicides becomes most prevalent. Protox-resistant common waterhemp were treated with herbicides at the 2-leaf, 4- to 6-leaf, and 8- to 10-leaf growth stage. Acifluorfen and fomesafen at 420 g ha−1 gave greater than 90% control at the 2-leaf stage and 4- to 6-leaf stage, except in 2003 when control was 85% with acifluorfen. In 2003 and 2004, common waterhemp control at the 8- to 10-leaf stage ranged between 54 and 75% with acifluorfen or fomesafen. Results indicate that common waterhemp resistance to customary rates of POST protox-inhibiting herbicides becomes prevalent after the 4- to 6-leaf growth stage. Nomenclature: Acifluorfen; azafenidin; bentazon; flumioxazin; fomesafen; lactofen; oxyfluorfen; sulfentrazone; common waterhemp, Amaranthus rudis Sauer AMATA.

Response of Common Lambsquarters (Chenopodium Album) to Glyphosate as Affected by Growth Stage

Abstract Experiments were conducted to determine the efficacy of glyphosate on four common lambsquarters populations collected from Kansas, Nebraska, North Dakota, and Ohio. Glyphosate dose-response studies for common lambsquarters treated at 2.5-, 7.5-, and 15-cm heights showed that glyphosate at 1.1 kg ae ha−1 caused more than 80% injury to 2.5-cm plants but less than 55% injury to 7.5- and 15-cm plants. All populations were susceptible to glyphosate at the 2.5-cm height. The glyphosate rate required to cause 50% injury (GR50) was 430, 500, 500, and 560 g ha−1 for the Kansas, North Dakota, Ohio, and Nebraska populations, respectively. Differential response of common lambsquarters populations was evident with 15-cm plants where the GR50 was glyphosate at 1,010, 1,230, 1,650, and 2,770 g ha−1 for the Kansas, North Dakota, Nebraska, and Ohio populations, respectively. Reduced injury on 15-cm common lambsquarters plants by glyphosate may be partly attributed to reduced glyphosate accumulation per unit of plant tissues and enhanced calcium content in more-developed plants. All four common lambsquarters populations at the early seedling stage were susceptible to glyphosate, but tolerance increased as the plant developed and the extent of tolerance differed among populations. Nomenclature: Glyphosate common lambsquarters, Chenopodium album L. CHEAL.

Survey of Common Waterhemp (Amaranthus rudis) Response to Protox- and ALS-Inhibiting Herbicides in Northeast Kansas'

A population of common waterhemp in northeast Kansas was confirmed resistant to protoporphyrinogen oxidase (protox)-inhibiting herbicides in 2001. In 2002, seeds were collected from 28 sites in a 16-km radius surrounding the site where resistance was confirmed to determine the extent of protox resistance in common waterhemp populations throughout the area. In addition, common waterhemp response to acetolactate synthase (ALS)-inhibiting herbicides and glyphosate was determined. At least one common waterhemp plant among the 48 plants tested from each of 10 sites was acifluorfen-resistant. These sites were randomly scattered throughout the sampling area, and resistance may have resulted from seed or pollen movement or independent development. Acifluorfen-resistant common waterhemp plants were initially injured by acifluorfen, but plants began recovering from injury within 14 days after treatment (DAT). All sites contained at least two common waterhemp plants with imazethapyr resistance, whereas plants from all sites were susceptible to glyphosate. Because acifluorfen- and imazethapyr-resistant common waterhemp populations are found in northeastern Kansas, protox-inhibiting and ALS-inhibiting herbicides may not provide common waterhemp control. Nomenclature: acifluorfen-methyl; glyphosate; imazethapyr; common waterhemp, Amaranthus rudis Sauer, #3 AMATA. Additional index word: Herbicide resistance. Abbreviations: ALS, acetolactate synthase [E.C. 2.2.1.6]; DAT, days after treatment; protox, protoporphyrinogen oxidase [E.C. 1.3.3.4].

Control of Protoporphyrinogen Oxidase Inhibitor-Resistant Common Waterhemp (Amaranthus rudis) in Corn and Soybean'

Field experiments were conducted in 2001 and 2002 to evaluate the efficacy of herbicides on protoporphyrinogen oxidase (protox, EC 1.3.3.4) inhibitor–resistant common waterhemp in corn and soybean. All corn herbicides tested gave greater than 90% common waterhemp control by 8 wk after postemergence herbicide treatment (WAPT). In soybean, common waterhemp control was less than 40% by 8 WAPT with postemergence protox-inhibiting herbicides lactofen and acifluorfen. However, preemergence protox-inhibiting herbicides sulfentrazone and flumioxazin gave greater than 85% common waterhemp control in both years. The greatest common waterhemp control in soybean was with glyphosate alone, alachlor + metribuzin, alachlor followed by (fb) glyphosate, and S-metolachlor + metribuzin fb glyphosate. Nomenclature: Acifluorfen; alachlor; flumioxazin; glyphosate; lactofen; S-metolachlor; metribuzin; sulfentrazone; common waterhemp, Amaranthus rudis Sauer #3 AMATA; corn, Zea mays L. # ZEAMX ‘RRX740RR’; soybean, Glycine max (L.) Merr. ‘Asgrow 3701’. Additional index words: Acetochlor, ALS-resistance, atrazine, bromoxynil, carfentrazone, clomazone, clopyralid, dicamba, diflufenzopyr, dimethenamid-P, flumetsulam, glufosinate, halosulfuron-methyl, imazamox, imazaquin, imazethapyr, isoxaflutole, mesotrione, pendimethalin, primisulfuron-methyl, prosulfuron, protox-resistance, thifensulfuron-methyl. Abbreviations: ALS, acetolactate synthase; proto, protoporphyrin IX; protogen, protoporphyrinogen IX; protox, protoporphyrinogen oxidase; WAPT, weeks after postemergence herbicide treatment.

Cotton Response to Simulated Drift of Seven Hormonal-Type Herbicides

Field experiments were conducted at Manhattan and Hesston, KS, in 2004, and at Manhattan, KS, in 2005, to evaluate cotton response to seven hormonal-type herbicides. Herbicides 2,4-D amine, 2,4-D ester, clopyralid, picloram, fluroxypyr, triclopyr, and dicamba were each applied at 0, 1/100, 1/200, 1/300, and 1/400 of the herbicide use rates on cotton in the six- to eight-leaf stage. Herbicide use rates were 210 and 280 g ae/ha for fluroxypyr and clopyralid and 561 g ae/ha, for 2,4-D amine, 2,4-D ester, dicamba, picloram, and triclopyr. At 14 d after treatment (DAT), all herbicides caused leaf cupping and epinasty, except triclopyr and clopyralid, which caused severe bleaching and chlorosis. The order of visual injury ratings was 2,4-D ester > 2,4-D amine > picloram > dicamba > fluroxypyr > triclopyr > clopyralid. By 56 DAT, slight injury symptoms were observed on plants treated with all herbicides, except all rates of 2,4-D, from which symptoms were severe. All rates of 2,4-D and the highest rate of picloram caused more than 60% flower abortion. Ranking of fiber yield reduction after herbicide treatment was 2,4-D ester > 2,4-D amine > picloram > fluroxypyr > dicamba > clopyralid > triclopyr. This research demonstrated that cotton is extremely susceptible to simulated drift rates of 2,4-D and picloram, whereas clopyralid and triclopyr caused early injury, with minimal effect on cotton yield. Nomenclature: Tribufos; S,S,S-tributyl phosphorotrithioate; cotton, Gossypium hirsutum L. ‘PM 2145 RR’.

Fate of acifluorfen and lactofen in common waterhemp (Amaranthus rudis) resistant to protoporphyrinogen oxidase-inhibiting herbicides

Abstract Studies were conducted to determine acifluorfen and lactofen absorption, translocation, and metabolism in protox-inhibiting herbicide-susceptible and -resistant common waterhemp. Acifluorfen and lactofen absorption was similar in both biotypes. Herbicide absorption was 12% in both susceptible and resistant common waterhemp 6 h after treatment (HAT). Absorption increased to 32 and 42% in susceptible and resistant plants, respectively, at 72 HAT. Translocation was similar in both biotypes for both herbicides. Herbicide translocation out of the treated leaf ranged between 5 and 15%. In a separate study, resistant common waterhemp plants were treated with acifluorfen or lactofen, alone or with tridiphane. Acifluorfen or lactofen injury to resistant common waterhemp was not altered with the addition of tridiphane. Treatments of 14C-acifluorfen or -lactofen on susceptible and resistant common waterhemp resulted in similar lactofen metabolism in both biotypes, but acifluorfen was not metabolized in either biotype within 24 HAT. This data indicate that differences in herbicide absorption, translocation, or metabolism are not the mechanism of common waterhemp resistance to protox-inhibiting herbicides. Nomenclature: Acifluorfen; lactofen; tridiphane; common waterhemp, Amaranthus rudis Sauer AMATA.

Prairie cupgrass (Eriochloa contract) and windmillgrass (Chloris verticillata) response to glyphosate and acetyl-CoA carboxylase–inhibiting herbicides

Abstract A greenhouse experiment was conducted to determine the efficacy of glyphosate and acetyl-CoA carboxylase (ACCase)–inhibiting herbicides sethoxydim, clethodim, and quizalofop on prairie cupgrass and windmillgrass. Herbicides were applied at seedling, tillering, and heading growth stages. In addition, a study to determine glyphosate absorption and translocation in both species was conducted. Herbicide treatments were glyphosate at 541, 841, and 1121 g ha−1 and sethoxydim, clethodim, and quizalofop at 350, 210, and 70 g ha−1, respectively. In general, control of prairie cupgrass and windmillgrass increased as the rate of glyphosate increased. In addition, windmillgrass was less susceptible to glyphosate at heading and seedling stages than was prairie cupgrass. Efficacy of all ACCase-inhibiting herbicides applied at any growth stage was equal to or greater than efficacy of the highest rate of glyphosate applied at the same stage. Furthermore, all herbicide treatments were more phytotoxic to prairie cupgrass and windmillgrass at seedling stage than at tillering or heading. Differential response of prairie cupgrass and windmillgrass to glyphosate was attributed to differences in glyphosate translocation. Separate field experiments were conducted to evaluate preemergence (PRE) and postemergence (POST) herbicide treatments for prairie cupgrass and windmillgrass in no-till corn at Hays, KS, in 2001 and 2002. All PRE treatments provided at least 90% control of windmillgrass in both years 6 wk after treatment (WAT). Prairie cupgrass was controlled effectively by acetochlor plus atrazine, alachlor plus atrazine, and S-metolachlor plus atrazine in 2001. In 2002, the only PRE treatments that gave 90% control or greater of prairie cupgrass 6 WAT were alachlor plus atrazine and pendimethalin plus atrazine. Glyphosate sequential treatment was the only POST treatment that provided 100% control of prairie cupgrass and windmillgrass in both years. Nomenclature: Acetochlor; alachlor; atrazine; clethodim; pendimethalin; quizalofop; sethoxydim; S-metolachlor; prairie cupgrass, Eriochloa contracta Hitchc. ERBCO; windmillgrass, Chloris verticillata Nutt. CHRVE; corn, Zea mays L.

Inheritance of resistance of common waterhemp (Amaranthus rudis) to protoporphyrinogen oxidase-inhibiting herbicide

Abstract Common waterhemp resistance to protoporphyrinogen oxidase (protox)-inhibiting herbicides was first reported in northeast Kansas in 2001. The objective of this research was to determine the inheritance characteristics of the protox-resistance trait. Resistant and susceptible common waterhemp were screened for resistance and inbred lines were developed using full-sib mating for three generations in the greenhouse. After the third generation, resistant and susceptible plants were crossed in a male and female reciprocal manner creating 57 F1 (first generation) lines. A proportion of the F1 progeny was screened for resistance and the remaining progeny were used to create F2 (second generation) and backcross (BC) lines. Approximately 500, 400, and 1400 F1, BC, and F2 progeny, respectively, were treated with 105 g ha−1 of lactofen when plants reached the 8-node growth stage. Visual injury ratings were determined at 14 days after treatment and based on a scale of 0 = no injury and 100 = mortality. A plant was considered to be resistant when visible injury was less than 50%. Approximately 91 and 93% of F1 progeny from susceptible female × resistant male and resistant female × susceptible male crosses, respectively, were scored as being resistant. There was no evidence of reciprocal differences or segregation in the F1 indicating the resistance trait is dominant and contained in the nucleus. F2 progenies supported a 3:1 genetic ratio and BC progenies supported a 1:1 ratio using a Chi-squared goodness-of-fit test. These results indicate resistance to protox-inhibiting herbicides is determined by a major dominant nuclear gene.

Effect of Management Practices on Double-Crop Soybean Yields

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