P. Roy Vidrine

Control of Volunteer Glyphosate-Resistant Cotton in Glyphosate-Resistant Soybean'

Cotton boll weevil has been eradicated from much of the U.S. Cotton Belt. After eradication, a containment program is necessary to detect and destroy reintroduced boll weevils. Crops other than cotton are not monitored for boll weevil, hence fruit on volunteer glyphosate-resistant (GR) cotton in GR soybean could provide oviposition sites for boll weevils and allow the insects to build up undetected. An experiment was conducted at five locations to evaluate control of GR cotton and reduction in cotton fruit production by herbicides commonly used on GR soybean. Cotton control by preemergence (PRE) or postemergence (POST) herbicides alone was inconsistent across locations. Flumetsulam at 45 g ai/ha, imazaquin at 137 g ai/ha, and metribuzin at 360 g ai/ha plus chlorimuron at 60 g ai/ha applied PRE controlled cotton 55 to 100% and reduced cotton fruit production 84 to 100%. Sulfentrazone at 167 g ai/ha plus chlorimuron at 34 g/ha PRE controlled cotton 50 to 91% and reduced fruit 48 to 98%. Metribuzin PRE at 420 g/ha controlled cotton 23 to 97% and reduced fruit 32 to 100%. Flumiclorac at 30 g ai/ha, 2,4-DB dimethylamine salt at 35 g ae/ha, chlorimuron at 12 g ai/ha, and the sodium salt of fomesafen at 420 g ai/ha mixed with glyphosate and applied POST controlled cotton 48 to 100% and reduced fruit production 67 to 100%. Cloransulam at 12 or 18 g ai/ha controlled cotton 3 to 66% and reduced fruit production 5 to 85%. Cotton control and fruit reduction were greatest and most consistent with sequential applications of metribuzin plus chlorimuron PRE followed by chlorimuron, flumiclorac, fomesafen, or 2,4-DB POST. These treatments controlled cotton at least 95% at all locations. Cotton fruit was totally eliminated at three locations and reduced at least 97% at a fourth location. Nomenclature: Chlorimuron; cloransulam; 2,4-DB; flumetsulam; flumiclorac; fomesafen; glyphosate; metribuzin; sulfentrazone; cotton, Gossypium hirsutum L. ‘DP 422 B/RR’, ‘PM 1218 B/RR’; soybean, Glycine max (L.) Merr. ‘A5353RR’, ‘A5802RR’, ‘A5901RR’. Additional index words: Boll weevil eradication, chlorimuron, cloransulam, flumetsulam, flumiclorac, fomesafen, metribuzin, oviposition sites, sulfentrazone, 2,4-DB. Abbreviations: DAP, days after planting; GR, glyphosate-resistant; POST, postemergence; PRE, preemergence.

Evaluation of Reduced Rates of Glyphosate and Chlorimuron in Glyphosate-Resistant Soybean (Glycine max)1

Abstract: Field studies were conducted over 2 yr in Louisiana to evaluate entireleaf morningglory and hemp sesbania control by glyphosate isopropylamine salt applied alone at 420, 560, and 700 g ae/ha and in combination with chlorimuron at 4, 6, 9, and 11 g ai/ha. Comparison treatments included glyphosate alone at 840 g/ha, glyphosate at 1,400 g/ha plus chlorimuron at 13 g/ha, and sethoxydim at 210 g ai/ha plus chlorimuron at 11 g/ha. Entireleaf morningglory and hemp sesbania were controlled no more than 77% with glyphosate rates as high as 840 g/ha. Chlorimuron added to glyphosate increased entireleaf morningglory control in two of the three experiments to 83 to 88% and hemp sesbania control to 86 to 98%. Response to chlorimuron was not rate dependent. In most cases, glyphosate–chlorimuron mixtures did not antagonize barnyardgrass control, and increasing rate of glyphosate did not always increase control. Soybean was injured no more than 6% by chlorimuron at one location, but injury was as great as 30% at another location, which was possibly due to smaller soybean size. Differences in weed control and soybean injury among the glyphosate and glyphosate–chlorimuron combinations were not reflected in soybean yields. Because injury occurred early season, sufficient time remained for soybean to recover and produce acceptable yields. Weed control by sethoxydim plus chlorimuron was less consistent than that by glyphosate plus chlorimuron, and soybean yield in most cases was inferior to the glyphosate treatments. Nomenclature: Chlorimuron; glyphosate; sethoxydim; barnyardgrass, Echinochloa crus-galli (L.) Beauv. #3 ECHCG; entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray # IPOHG; hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex. A. W. Hill # SEBEX; soybean, Glycine max (L.) Merr. Additional index words: Herbicide mixtures, transgenic soybean. Abbreviation: WAT, week after treatment.

Glyphosate Efficacy on Selected Weed Species Is Unaffected by Chemical Coapplication1

A study was conducted in 2004 to determine the effect of coapplication of the insecticides acephate, acetamiprid, bifenthrin, cyfluthrin, cypermethrin, dicrotophos, dimethoate, emanectin benzoate, imidacloprid, indoxacarb, lambda-cyhalothrin, methoxyfenozide, spinosad, thiamethoxam, and zeta-cypermethrin; the plant growth-regulator mepiquat pentaborate; a foliar sodium calcium borate micronutrient solution; and a foliar nitrogen fertilizer solution with glyphosate on the efficacy of weeds that commonly infest cotton. Barnyardgrass, hemp sesbania, johnsongrass, pitted morningglory, and sicklepod were grown in outdoor containers and treated with glyphosate at 1,120 g ai/ha alone or in coapplication at the three-to four- or seven-to eight-leaf growth stage. Glyphosate efficacy, based on visual control ratings at 7, 14, and 28 d after treatment (DAT) and fresh weight reduction of weed biomass at 28 DAT, was unaffected by chemical coapplication or application timing. Averaged across application timing and visual rating interval, glyphosate alone controlled barnyardgrass 97%, hemp sesbania 68%, johnsongrass 98%, pitted morningglory 68%, and sicklepod 89%. These results indicate that glyphosate coapplications evaluated offer producers the ability to combine pest and crop management strategies and reduce application costs without sacrificing control of weeds evaluated. Nomenclature: Acephate; acetamiprid; bifenthrin; cyfluthrin; cypermethrin; dicrotophos; dimethoate; emanectin benzoate; glyphosate; imidacloprid; indoxacarb; lambda-cyhalothrin; mepiquat pentaborate; methoxyfenozide; nitrogen fertilizer solution, (18.8% urea nitrogen and 6.2% water-soluble nitrogen); sodium calcium borate 10%; spinosad; thiamethoxam; zeta-cypermethrin; barnyardgrass, Echinochloa crus-galli (L.) P. Beauv. #3 ECHCG; hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex A. W. Hill # SEBEX; johnsongrass, Sorghum halepense (L.) Pers. # SORHA; pitted morningglory, Ipomoea lacunosa L. # IPOLA; sicklepod, Senna obtusifolia (L.) Irwin and Barneby # CASOB. Additional index words: Herbicide–insecticide combinations, pesticide compatibility. Abbreviations: DAT, days after treatment; RCB, randomized complete block.

Reduced-Input, Postemergence Weed Control with Glyphosate and Residual Herbicides in Second-Generation Glyphosate-Resistant Cotton

Field studies were conducted 2004 and 2005 to evaluate weed control following POST applications of glyphosate in combination with either S-metolachlor (premix formulation), pyrithiobac, or trifloxysulfuron in conjunction with glyphosate in second-generation glyphosate-resistant cotton (Roundup Ready Flex). These herbicides were applied in combination with glyphosate in a two-application program at the 2-leaf (LF) (followed by glyphosate alone at the 10-LF growth stage), 6-LF (following glyphosate alone at the 2-LF growth stage), or 10-LF (following glyphosate alone at the 2-LF growth stage) cotton growth stages. No differences in weed control between residual herbicide were observed for goosegrass, hemp sesbania, Johnsongrass, Palmer amaranth, redroot pigweed, sicklepod, or smellmelon. Optimum control of barnyardgrass and browntop millet was achieved with glyphosate plus S-metolachlor. No differences were observed among application timings for control of goosegrass, hemp sesbania, Johnsongrass, pitted morningglory, and smellmelon. Control of barnyardgrass, browntop millet, Palmer amaranth, redroot pigweed, and sicklepod was optimized with residual herbicide application at the 2- or 10-LF timing. No yield differences were observed between residual herbicides, and seed cotton yield averaged 2,800 kg/ha. Yield was maximized when residual herbicide was applied at the 2- or 10-LF growth stage (2,960 to 2,730 kg/ha). Analysis based on numerical yield at particular residual-herbicide application timings and calculated yield for each timing based on the percentage of a standard three-application glyphosate program indicated the most consistent residual-herbicide timing for optimizing yield in a reduced-input Roundup Ready Flex weed-control program occurred at the two-leaf growth stage. All reduced-input programs, however, resulted in cotton yield of at least 93% of that obtained with the standard program. Nomenclature: Glyphosate; pyrithiobac; S-metolachlor; trifloxysulfuron; barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG; browntop millet, Urochloa ramosa (L.) Nguyen PANRA; goosegrass, Eleusine indica (L.) Gaertn ELEIN; hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex A. W. Hill SEBEX; Johnsongrass, Sorghum halepense (L.) Pers. SORHA; Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; pitted morningglory, Ipomoea lacunosa L. IPOLA; redroot pigweed, Amaranthus retroflexus L. AMARE; sicklepod, Senna obtusifolia (L.) H.S. Irwin & Barneby CASOB; smellmellon, Cucumis melo L. CUMMD; cotton, Gossypium hirsutum L.

Second-generation Glyphosate-Resistant Cotton Tolerance to Combinations of Glyphosate with Insecticides and Mepiquat Chloride

Field trials were conducted in 2005 and 2006 to evaluate application of glyphosate alone or plus the plant growth regulator mepiquat chloride with 20 different insecticides to second-generation glyphosate-resistant cotton at the pinhead square or first bloom growth stages. At 7 DAT, averaged across cotton growth stages and herbicide treatments, combination with insecticides profenofos and methomyl resulted in 5 and 9% plant injury, respectively, and were the only insecticide combinations that resulted in injury greater than glyphosate or glyphosate plus mepiquat chloride applied alone. By 14 DAT, cotton injury was less than 2% for all treatments. Averaged across cotton growth stages and insecticides, addition of mepiquat chloride to glyphosate resulted in a 4 and 6 cm height reduction at 7 and 28 DAT, respectively. Seed cotton yield and percent first harvest were similar for all treatments, indicating that cotton injury and height reductions observed after application did not result in yield reductions or maturity delays. Glyphosate combined with insecticides and mepiquat chloride, in accordance with herbicide labeling for second-generation glyphosate-resistant cotton, offers producers the ability to integrate pest and crop management strategies and reduce application costs with minimal effect on the crop. Nomenclature: Acephate, acetamiprid, bifenthrin, cyfluthrin, cypermethrin, dicrotophos, dimethoate, emamectin benzoate, gamma-cyhalothrin, glyphosate, imidacloprid, indoxacarb, lambda-cyhalothrin, mepiquat chloride, methomyl, novaluron, oxamyl, profenofos, spinosad, thiamethoxam, thiodicarb, zeta-cypermethrin, cotton, Gossypium hirsutum L

Effectiveness of Preemergence Herbicide and Postemergence Glyphosate Programs in Second-Generation Glyphosate-resistant Cotton

A study was conducted in 2004 and 2005 to evaluate the benefit of applying fluometuron PRE versus glyphosate-only POST programs in second-generation GR cotton (Roundup Ready Flex®). Fluometuron was either included or excluded with POST application timings of glyphosate at the following cotton growth stages: (1) 3 leaf (lf) followed by (fb) 7 lf fb 14 lf (over the top) OT (2) 3 fb 7 lf OT (3) 7 lf OT fb 14 lf postemergence directed (PD), and (4) 7 fb 14 lf OT. Control of goosegrass, Palmer amaranth, pitted morningglory, sicklepod, and smellmelon was increased 2 to 8 percentage points with the addition of fluometuron PRE. The inclusion of fluometuron PRE did not improve control of barnyardgrass, browntop millet, hemp sesbania, johnsongrass, or redroot pigweed and control ranged from 81% to 84%, 69% to 75%, 94% to 94%, 87% to 89%, and 92% to 93%, respectively. By 56 d after the last POST application, control of johnsongrass, Palmer amaranth, pitted morningglory, and smellmelon was at least 83%, 93%, 92%, and 86%, respectively, with only slight differences noted among POST glyphosate programs. Control of barnyardgrass, browntop millet, and redroot pigweed was 68%, 47%, 86%, respectively, with the POST glyphosate program of 3 fb 7 lf OT, which was significantly less than all other glyphosate POST programs. Cotton yield increased 32% and 36% with the addition of fluometuron PRE to glyphosate POST programs consisting of 7 lf OT fb 14 lf PD and 7 lf fb 14 lf OT, respectively. Cotton yield for other glyphosate POST programs including an earlier 3 lf application was not improved when fluometuron was applied PRE. Without inclusion of fluometuron PRE, yield was maximized with the glyphosate POST program that included three applications of glyphosate (2,510 kg/ha). Overall, this research emphasizes the fact that weed control is important in the early season as well as in the late season in second-generation GR cotton. Nomenclature: Fluometuron; glyphosate; barnyardgrass; Echinochloa crus-galli (L.) Beauv. ECHCG; browntop millet, Urochloa ramosa (L.) Nguyen PANRA; goosegrass, Eleusine indica (L.) Gaertn. ELEIN; hemp sesbania, Sesbania herbacea (P. Mill.) McVaugh SEBEX; johnsongrass, Sorghum halepense (L.) Pers. SORHA; Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; pitted morningglory, Ipomoea lacunosa L. IPOLA; redroot pigweed, Amaranthus retroflexus L. AMARE; sicklepod, Senna obtusifolia (L.) Irwin and Barneby CASOB; smellmelon, Cucumis melo L. CUMMD; cotton, Gossypium hirsutum L.