Jon Scott

Dose–Response Curves of Kih-485 for Preemergence Weed Control in Corn

Abstract Field experiments were conducted in Nebraska with the experimental herbicide KIH-485 on soils with three different levels of organic matter (OM) to ascertain a dose response for weed control and corn tolerance. Dose–response curves based on the log-logistic model were used to determine the effective dose that provides 90% weed control (ED90 values) for three grasses (green foxtail, field sandbur, large crabgrass) and two broadleaf weeds (velvetleaf, tall waterhemp). The ED90 values for green foxtail control were 143, 165, and 202 g ai/ha for soils with 1, 2, and 3% OM, respectively at 28 d after treatment (DAT). The highest dose of 371 g ai/ha was needed for field sandbur control at 28 DAT, compared with 141 g ai/ha for large crabgrass, 152 g ai/ha for tall waterhemp, and 199 g ai/ha for velvetleaf. There was no significant corn injury observed. Grain yield increased with increasing doses of KIH-485; optimum yield was achieved at about 195 g ai/ha. From the dose–response curves it is clear that the proposed label rate of KIH-485 of 200 to 300 g ai/ha will provide excellent control of most grasses and certain broadleaf weeds in corn for at least the first 4 wk of the growing season on soils up to 3% OM in the state of Nebraska. Nomenclature: KIH-485 (proposed common name pyrasulfatole), 3-[(5-difluoromethoxy-1-methyl-3-trifluoromethylpyrazol-4-yl)-methylsulfonyl]-4,5-dihydro-5,5-dimethylisoxazole; green foxtail, Setaria viridis (L.) Beauv.; field sandbur, Cenchrus spinifex Cav.; large crabgrass, Digitaria sanguinalis (L.) Scop.; tall waterhemp, Amaranthus tuberculatus (Moq.); velvetleaf, Abutilon theophrasti Medicus; corn, Zea mays L

Adjuvants Influenced Saflufenacil Efficacy on Fall-Emerging Weeds

Abstract Saflufenacil is a new herbicide being developed for preplant burndown and PRE broadleaf weed control in field crops, including corn, soybean, sorghum, and wheat. Field experiments were conducted in 2006 and 2007 at Concord, in northeast Nebraska, with the objective to describe dose–response curves of saflufenacil applied with several adjuvants for broadleaf weed control. Dose–response curves based on log-logistic model were used to determine the effective dose that provides 90% weed control (ED90) values for six broadleaf weeds (field bindweed, prickly lettuce, henbit, shepherds-purse, dandelion, and field pennycress). Addition of adjuvants greatly improved efficacy of saflufenacil. For example, the ED90 values for field bindweed control at 28 d after treatment were 71, 20, 11, and 7 g/ha for saflufenacil applied alone, or with nonionic surfactant (NIS), crop oil concentrate (COC), or methylated seed oil (MSO), respectively. MSO was the adjuvant that provided the greatest enhancement of saflufenacil across all species tested. COC was the second-best adjuvant and provided control similar to MSO on many weed species. NIS provided the least enhancement of saflufenacil. These results are very similar to the proposed label dose of saflufenacil for burndown weed control, which will range from 25 to 100 g/ha with MSO or COC. We believe that such a dose would provide excellent burndown control of most broadleaf weed species that emerge in the fall in Nebraska. Nomenclature: Saflufenacil; dandelion, Taraxacum officinale Weber; field bindweed, Convolvulus arvensis L.; field pennycress, Thlaspi arvense L.; henbit, Lamium amplexicaule L.; prickly lettuce, Lactuca serriola L.; shepherds-purse, Capsella bursa-pastoris (L.) Medik.; corn, Zea mays L.; sorghum, Sorghum bicolor (L.) Moench; soybean, Glycine max L.; wheat, Triticum aestivum L.

Problem weed control in glyphosate-resistant soybean with glyphosate tank mixes and soil-applied herbicides.

Abstract Although glyphosate controls many plant species, certain broadleaf weeds in Nebraskas cropping systems exhibit various levels of tolerance to the labeled rates of this herbicide, including ivyleaf morningglory, Venice mallow, yellow sweetclover, common lambsquarters, velvetleaf, kochia, Russian thistle, and field bindweed. Therefore, two field studies were conducted in 2004 and 2005 at Concord and North Platte, NE, to evaluate performance of (1) seven preemergence (PRE) herbicides and (2) glyphosate tank mixes applied postemergence (POST) at three application times for control of eight weed species that are perceived as problem weeds in glyphosate-resistant soybean in Nebraska. The PRE herbicides, including sulfentrazone plus chlorimuron, pendimethalin plus imazethapyr, imazaquin, and pendimethalin plus imazethapyr plus imazaquin provided more than 85% control of most weed species tested in this study 28 d after treatment (DAT). However, sulfentrazone plus chlorimuron and pendimethalin plus imazethapyr plus imazaquin were the only PRE treatments that provided more than 80% control of most weed species 60 DAT. In the POST glyphosate tank-mix study, the level of weed control was significantly affected by the timing of herbicide application; control generally decreased as weed height increased. In general, glyphosate tank mixes applied at the first two application times (early or mid-POST) with half label rates of lactofen, imazamox, imazethapyr, fomesafen, imazaquin, or acifluorfen, provided more than 80% control of all species that were 20 to 30 cm tall except ivyleaf morningglory, Venice mallow, yellow sweetclover, and field bindweed. Glyphosate tank mixes applied late POST with lactofen, imazethapyr, or imazaquin provided more than 70% control of common lambsquarters, velvetleaf, kochia, and Russian thistle that were 30 to 50 cm tall. Overall, glyphosate tank mixes with half label rates of chlorimuron or acifluorfen were the best treatments; they provided more than 80% control of all the studied weed species when applied at early growth stages. Results of this study suggested that mixing glyphosate with other POST broadleaf herbicides, or utilizing soil-applied herbicides after crop planting helped effectively control most problematic weeds in glyphosate-resistant soybean in Nebraska. Nomenclature: Acifluorfen; chlorimuron; fomesafen; glyphosate; imazamox; imazaquin; imazethapyr; lactofen; pendimethalin; sulfentrazone; common lambsquarters, Chenopodium album L. CHEAL; field bindweed, Convolvulus arvensis L. CONAR; ivyleaf morningglory, Ipomoea hederacea Jacq. IPOHE; kochia, Kochia scoparia (L.) Schrad. KCHSC; Russian thistle, Salsola tragus L. SASKR; velvetleaf, Abutilon theophrasti Medik. ABUTH; Venice mallow, Hibiscus trionum L. HIBTR; yellow sweetclover, Melilotus officinalis (L.) Lam. MEUOF; soybean, Glycine max L.

Confirmation and Control of HPPD-Inhibiting Herbicide–Resistant Waterhemp (Amaranthus tuberculatus) in Nebraska

Field and greenhouse experiments were conducted in Nebraska to (1) confirm the 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting resistant-waterhemp biotype (HPPD-RW) by quantifying the resistance levels in dose-response studies, and (2) to evaluate efficacy of PRE-only, POST-only, and PRE followed by POST herbicide programs for control of HPPD-RW in corn. Greenhouse dose-response studies confirmed that the suspected waterhemp biotype in Nebraska has evolved resistance to HPPD-inhibiting herbicides with a 2- to 18-fold resistance depending upon the type of HPPD-inhibiting herbicide being sprayed. Under field conditions, at 56 d after treatment, ≥90% control of the HPPD-RW was achieved with PRE-applied mesotrione/atrazine/S-metolachlor+acetochlor, pyroxasulfone (180 and 270 g ai ha−1), pyroxasulfone/fluthiacet-methyl/atrazine, and pyroxasulfone+saflufenacil+atrazine. Among POST-only herbicide programs, glyphosate, a premix of mesotrione/atrazine tank-mixed with diflufenzopyr/dicamba, or metribuzin, or glufosinate provided ≥92% HPPD-RW control. Herbicide combinations of different effective sites of action in mixtures provided ≥86% HPPD-RW control in PRE followed by POST herbicide programs. It is concluded that the suspected waterhemp biotype is resistant to HPPD-inhibiting herbicides and alternative herbicide programs are available for effective control in corn. The occurrence of HPPD-RW in Nebraska is significant because it limits the effectiveness of HPPD-inhibiting herbicides. Nomenclature Acetochlor, atrazine, glyphosate, clopyralid, dicamba, diflufenzopyr, dimethenamid-P, flumetsulam, fluthiacet-methyl, glufosinate, isoxaflutole, mesotrione, metribuzin, pyroxasulfone, S-metolachlor, saflufenacil, rimsulfuron, tembotrione, thiencarbazone-methyl, topramezone, waterhemp, Amaranthus tuberculatus (Moq.) Sauer, corn, Zea mays L. Se realizaron experimentos de campo y de invernadero en Nebraska para (1) confirmar un biotipo de Amaranthus tuberculatus resistente a inhibidores de 4-hydroxyphenylpyruvate dioxygenase (HPPD) (HPPD-RW) cuantificando el nivel de resistencia con estudios de respuesta a dosis, y (2) evaluar la eficacia de programas de herbicidas para el control de HPPD-RW en maíz con sólo herbicidas PRE, sólo POST, y herbicidas PRE seguidos por POST. Los estudios de respuesta a dosis en invernadero confirmaron que el biotipo de A. tuberculatus en Nebraska ha evolucionado resistencia a herbicidas inhibidores de HPPD con 2 a 18 veces mayor resistencia dependiendo del tipo de herbicida inhibidor de HPPD que se aplicó. Bajo condiciones de campo, a 56 d después del tratamiento, se alcanzó ≥90% de control de HPPD RW con aplicaciones PRE de mesotrione/atrazine/S-metolachlor + acetochlor, pyroxasulfone (180 y 270 g ai ha−1), pyroxasulfone/fluthiacet-methyl/atrazine, y pyroxasulfone + saflufenacil + atrazine. Entre los programas de herbicidas con sólo POST, glyphosate, una premezcla de mesotrione/atrazine mezclados en tanque con diflufenzopyr/dicamba, o metribuzin, o glufosinate brindaron ≥92% control de HPPD-RW. Combinaciones de herbicidas efectivos con diferentes sitios de acción en mezclas brindaron ≥86% de control de HPPD-RW en programas de herbicidas PRE seguidos por POST. Se concluyó que el biotipo de A. tuberculatus es resistente a herbicidas inhibidores de HPPD y que hay programas de herbicidas alternativos disponibles para su control efectivo en maíz. La ocurrencia de HPPD-RW en Nebraska es significativa porque limita la efectividad de herbicidas inhibidores de HPPD.

Sensitivity of Grape and Tomato to Micro-rates of Dicamba-based Herbicides

There is Agro-climatic concern that the widespread use of dicamba-based herbicides in Dicamba-Tolerant (DT) soybeans can result in un-intended drift onto non-DT crops in nearby field due to windy conditions and volatility. New dicamba-based products such as Engenia® and XtendiMax® with Vapor Grip technology were developed to reduce volatility, however, they are not completely volatile-free. A study was conducted to evaluate the sensitivity of pot-grown grape and tomato to six micro-rates of three dicamba-based products (Clarity®, Engenia® and XtendiMax®) in 2016 and 2017, at Haskell Ag Lab, Concord (42.37oN, 96.68oW), NE, USA. The tested dicamba formulations negatively impacted growth of grape and tomato as measured by vine length and plant height respectively, as well as by plant biomass. About 2% of the label rate was high enough to cause 50% injury and reduction in vine length or plant height. For example, a dose of 6.54 to 9.13 g ae ha-1 and 3.98 to 5.35 g ae ha-1 caused 50% injury in grape and tomato respectively, at 21 DAT. At 50% injury and vine reduction threshold, grape appeared more sensitive to XtendiMax® than Clarity® and Engenia®. For instance, a dose of 1.83 g ae ha-1 of XtendiMax® was required to cause 50% reduction in vine length (~49 cm) compared to significantly higher dose of 5.64 and 7.59 g ae ha-1 required for Clarity® and Engenia®, respectively. However, in tomato, there was no significant difference in sensitivity to all three products. In general, the present study showed that grape and tomato were very sensitive to micro-rates of all three dicamba products, irrespective of the of the new dicamba technology that reduces volatility. Hence, efforts should be made to avoid drift of dicamba onto these crops.

Lythrum salicaria (Purple Loosestrife) Control with Herbicides: Multiyear Applications

Abstract This study evaluated the effectiveness of 14 herbicide treatments for purple loosestrife (Lythrum salicaria L.) control over a period of 10 yr. The study commenced in 2000/2001 at four wetland locations in Nebraska. The evaluated herbicides included: glyphosate at 2.2 and 3.4 kg ha-1; 2,4-D dimethylamine at 1.4 and 2.8 kg ae ha-1; triclopyr at 1.3 and 2.1 kg ae ha-1 imazapyr at 1.1 and 1.7 kg ae ha-1; metsulfuron at 0.042 and 0.084 ai kg ha-1; fosamine at 13.5 and 22.4 kg ai ha-1; triclopyr at 1.3 kg ae ha-1 plus 2,4-D amine at 1.4 ae kg ha-1; and metsulfuron at 0.042 kg ai ha-1 plus 2,4-D amine at 1.4 kg ae ha-1. Some treatments provided excellent control (90%) that lasted only one season, while others suppressed L. salicaria growth for multiple seasons, depending on the location and the age of L. salicaria stand. Application of higher rates of glyphosate, imazapyr, and metsulfuron consistently provided excellent control (≥90%) of L. salicaria that lasted 360 d after treatment at most locations. Application of fosamine and the lower rate of 2,4-D amine provided the least L. salicaria control at most locations. The older the L. salicaria stand, the more multiple applications of herbicides were needed to completely control L. salicaria. Generally, there were higher percentages of grasses in the 2,4-D-, triclopyr-, and metsulfuron-treated plots compared with higher percentages of broadleaf species in the glyphosate- and imazapyrtreated plots at each location.