Marilyn R. McClelland

Herbicide Resistance: Toward an Understanding of Resistance Development and the Impact of Herbicide-Resistant Crops

This is the publisher’s final pdf. The published article is copyrighted by the Weed Science Society of America and can be found at: http://wssajournals.org/loi/wees. To the best of our knowledge, one or more authors of this paper were federal employees when contributing to this work.

Rice and red rice interference. II. Rice response to population densities of three red rice (Oryza sativa) ecotypes

Abstract Red rice, which grows taller and produces more tillers than domestic rice and shatters most of its seeds early, is a major weed in many rice-growing areas of the world. Field experiments were conducted at Stuttgart, AR in 1997 and 1998 to evaluate the growth response of the Kaybonnet (KBNT) rice cultivar to various population densities of three red rice ecotypes. The ecotypes tested were Louisiana3 (LA3), Stuttgart strawhull (Stgstraw), and Katy red rice (KatyRR). Compared with KBNT alone, LA3, the tallest of the three red rice ecotypes, reduced tiller density of KBNT 51%, aboveground biomass at 91 d after emergence (DAE) 35%, and yield 80%. Stgstraw, a medium-height red rice, reduced KBNT tiller density 49%, aboveground biomass 26%, and yield 61%. KatyRR, the shortest red rice, reduced KBNT tiller density 30%, aboveground biomass 16%, and yield 21%. Tiller density of rice was reduced by 20 to 48% when red rice density increased from 25 to 51 plants m−2. Rice biomass at 91 DAE was reduced by 9 and 44% when red rice densities were 16 and 51 plants m−2. Rice yield was reduced by 60 and 70% at red rice densities of 25 and 51 plants m−2, respectively. These results demonstrate that low populations of red rice can greatly reduce rice growth and yield and that short-statured red rice types may affect rice growth less than taller ecotypes. Nomenclature: Red rice, Oryza sativa L. ORYSA, ‘KatyRR’, ‘LA3’, ‘Stgstraw’; rice, Oryza sativa L., ‘Kaybonnet’.

Evaluation of Cereal and Brassicaceae Cover Crops in Conservation-Tillage, Enhanced, Glyphosate-Resistant Cotton

Abstract Research was conducted for 2 yr at Marianna, AR, to determine whether the fall-planted cover crops rye, wheat, turnip, and a blend of brown and white mustard (Caliente) would aid weed management programs in conservation-tilled, enhanced, glyphosate-resistant cotton. Wheat and rye easily were established both years and turnip and mustard blend stands were better in the second year. The cover crops alone were more suppressive of Palmer amaranth, pitted morningglory, and goosegrass in 2007 than in 2008. Rye was generally superior to wheat in suppressing the three evaluated weeds. Once herbicides were applied, there were seldom differences among cover crops for a particular herbicide program as a result of the highly efficacious herbicide programs. Cotton yields were not affected by wheat, rye, or the mustard blend, but yields were lowest in plots that followed turnip both years, possibly because of allelopathy. Integration of cover crops, especially cereals, into conservation-tilled, glyphosate-resistant cotton aided early-season weed management and could reduce the selection of glyphosate for herbicide resistance. Nomenclature: Goosegrass, Eleusine indica (L.) Gaertn. ELEIN; Palmer amaranth, Amaranthus palmeri S. Wats AMAPA; pitted morningglory, Ipomoea lacunosa L. IPOLA; brown mustard, Brassica juncea (L.) Czern.; cotton, Gossypium hirsutum L; rye, Secale cereale L.; turnip, Brassica rapa L., wheat, Triticum aestivum L.; white mustard, Sinapis alba L

Evaluation of Legume Cover Crops and Weed Control Programs in Conservation-Tillage, Enhanced Glyphosate-Resistant Cotton

Abstract Research was conducted at Marianna, AR, for 2 yr to determine whether hairy vetch and Austrian winter pea cover crops would aid weed management programs in conservation-tilled, enhanced glyphosate-resistant cotton. Both cover crops were easily established and produced rapid growth in early spring, with biomass production of 435 to 491 g m−2 by Austrian winter pea and 415 to 438 g m−2 by hairy vetch. The effect of cover crops on weed control was short-lived in both years, with herbicide programs being the major determinant of weed control and seed-cotton yield. Averaged over cover crops, seed-cotton yields when the initial in-crop glyphosate application was delayed to the four-node cotton stage were up to 710 kg ha−1 less than in a PRE herbicide program. In 1 of 2 yr, seed-cotton yields were greater in PRE-treated plots compared with a program where initial weed management was delayed to the one-leaf stage of cotton. As a result of rapid decay of hairy vetch and Austrian winter pea biomass following cotton planting and the lack of adequate Palmer amaranth, pitted morningglory, and goosegrass control in the absence of herbicides, it appears there may be minimal weed management benefits from the use of hairy vetch and Austrian winter pea in Midsouth cotton production. Nomenclature: Goosegrass, Eleusine indica (L.) Gaertn. ELEIN; Palmer amaranth, Amaranthus palmeri S. Wats AMAPA; pitted morningglory, Ipomoea lacunosa L. IPOLA; Austrian winter pea, Pisum sativum L. ssp. arvense (L.) Poir.; cotton, Gossypium hirsutum L.; hairy vetch, Vicia villosa Roth.

Management of Acetolactate Synthase (ALS)-Resistant Common Cocklebur (Xanthium strumarium) in Soybean1

A fixed-plot management study for control of acetolactate synthase (ALS)–resistant common cocklebur in soybean was initiated in 1994 at Fayetteville, AR. Three susceptible and three imazaquin-resistant common cocklebur plants were transplanted into the field, and seed (burs) were distributed throughout the plots in the fall of 1994. Herbicide treatments included imazaquin, chlorimuron, and chlorimuron plus metribuzin applied each year from 1995 through 1999 and herbicide rotations containing ALS inhibitors and herbicides with alternative modes of action. Effectiveness of management systems and the dynamics of the development of common cocklebur resistance, including development of resistance to imazaquin and chlorimuron, were evaluated. Imazaquin controlled susceptible common cocklebur populations in 1995 but not the resistant population, resulting in significant soybean yield reduction. By the end of the 1996 season, the resistant biotype dominated imazaquin plots, and a high level of cross-resistance to chlorimuron was observed in the population. Resistant populations were reduced by non-ALS herbicide programs of sulfentrazone plus clomazone applied preemergence (PRE), metribuzin plus clomazone applied PRE followed by bentazon applied postemergence (POST), and transgenic herbicide programs of glyphosate and glufosinate applied POST. Rotating ALS inhibitors with non–ALS-inhibiting heribicides may slow the development of resistance, but resistant individuals may eventually dominate the population. Nomenclature: Bentazon; chlorimuron; clomazone; glufosinate; glyphosate; imazaquin; metribuzin; sulfentrazone; common cocklebur, Xanthium strumarium L. #3 XANST; soybean, Glycine max (L.) Merr. ‘Hutcheson’, ‘Delta King 5580’, ‘Delta King 5961RR’, ‘Asgrow 5547LL’. Additional index words: ALS resistance, atrazine, chlorimuron resistance, flumetsulam, fluometuron, fomesafen, herbicide resistance management, imazaquin resistance. Abbreviations: ALS, acetolactate synthase (EC 4.1.3.18); DAT, days after treatment; POST, postemergence; PRE, preemergence.

Injury Potential from Carryover of Watermelon Herbicide Residues

Studies were conducted to determine injury potential to rotational crops from carryover of herbicides used in watermelon production. Treatments included halosulfuron, ethalfluralin, and sulfentrazone alone; halosulfuron in tank mixtures with bensulide, clomazone, ethalfluralin, and naptalam; and a tank mixture of naptalam and bensulide. Sulfentrazone applied at 224 g ai/ha to watermelon severely reduced spinach emergence, but did not reduce emergence of broccoli, cabbage, or wheat. Residues of sulfentrazone applied to watermelon at 450 g/ha stunted growth of broccoli and cabbage and was the only treatment that reduced wheat stand. Injury to broccoli, cabbage, and spinach increased as the halosulfuron rate increased. Ethalfluralin did not reduce stand or cause injury to any of the four rotational crops. Naptalam plus bensulide did not reduce stand of the four crops and caused either slight or no injury. Residues of sulfentrazone and halosulfuron can injure vegetables following crops in which these herbicides are used, and caution should be taken particularly with spinach, broccoli, and cabbage in this respect. Nomenclature: Bensulide; clomazone; ethalfluralin; halosulfuron; naptalam; sulfentrazone; broccoli, Brassica oleracea var. botrytis (L.) ‘Everest’, ‘Green Sprouting Calabrese’; cabbage, Brassica oleracea var. capitata (L.) ‘Early Jersey Wakefield’; spinach, Spinacia oleracea (L.) ‘Cypress’, ‘F-380’; watermelon, Citrullus lanatus (Thunb.) ‘Jubilee’, ‘XIT 101’; hard red winter wheat, Triticum aestivum (L.) ‘Jagger’.

Preemergence Weed Control in Direct-Seeded Watermelon1

Studies were conducted at eight sites during a 3-yr period in Oklahoma and Arkansas to determine the effectiveness and safety of preemergence applications of halosulfuron both alone and in tank mixtures with bensulide, clomazone, ethalfluralin, and naptalam. Ethalfluralin, naptalam plus bensulide, and sulfentrazone also were applied alone. Although halosulfuron caused up to 20% seedling stunting, watermelon plants recovered by 5 to 7 wk after planting, and yield was similar to that of hand-weeded plots. Halosulfuron treatments controlled hophornbeam copperleaf, Palmer amaranth, carpetweed, and cutleaf groundcherry 80 to 100%. Control of goosegrass was at least 97% with clomazone plus ethalfluralin plus halosulfuron. Injury to watermelon treated with sulfentrazone ranged from 76 to 98% at 2 to 4 wk after treatment. This was reflected by yields that were lower than any other herbicide treatment in the studies. Nomenclature: Bensulide; clomazone; ethalfluralin; halosulfuron; naptalam; sulfentrazone; hophornbeam copperleaf, Acalypha ostryifolia Riddell #3 ACCOS; Palmer amaranth, Amaranthus palmeri S. Wats. # AMAPA; goosegrass, Eleusine indica (L.) Gaertn. # ELEIN; carpetweed, Mollugo verticillata L. # MOLVE; cutleaf groundcherry, Physalis angulata L. # PHYAN; watermelon, Citrullus lanatus ‘Jubilee’, ‘XIT 101’, ‘Crimson Sweet’. Additional index words: Broadleaf weed control, watermelon injury. Abbreviations: PRE, preemergence; WAT, weeks after treatment.