William A. Bailey

Economic assessment of weed management for transgenic and nontransgenic cotton in tilled and nontilled systems

Abstract Studies were conducted to evaluate weed management programs in nontransgenic, bromoxynil-resistant, and glyphosate-resistant cotton in nontilled and tilled environments. Tillage did not affect weed control provided by herbicides. Early-season stunting in nontilled cotton was 3% regardless of the herbicide system and was no longer evident at midseason. Cotton yield was 10 to 15% greater, on an average, under tilled conditions than that under nontilled conditions. Excellent (> 90%) common lambsquarters, entireleaf morningglory, ivyleaf morningglory, jimsonweed, pitted morningglory, prickly sida, tall morningglory, and velvetleaf control was achieved with treatments containing pyrithiobac, bromoxynil, and glyphosate. Preemergence (PRE) or postemergence-directed (PD) herbicide inputs were necessary for adequate large crabgrass and goosegrass control. Bromoxynil and pyrithiobac postemergence did not control sicklepod unless supplemented with MSMA and followed by a late-postdirected treatment of cyanazine plus MSMA. Treatments that included glyphosate controlled sicklepod regardless of the late-PD treatment. Economic returns were at least

Virginia Market-Type Peanut (Arachis hypogaea) Cultivar Tolerance and Yield Response to Flumioxazin Preemergence1

930 ha−1 and not different from the higher yielding programs in nontransgenic cotton when fluometuron applied PRE was included in the bromoxynil programs. Late-season weed control was usually greater than 90% from glyphosate programs, and net returns from glyphosate programs were as high or higher than the net returns from programs that used midseason treatments of bromoxynil, pyrithiobac, or fluometuron plus MSMA. Nomenclature: Bromoxynil; cyanazine; fluometuron; glyphosate; MSMA; pendimethalin; pyrithiobac; common lambsquarters, Chenopodium album L. CHEAL; entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray IPOHG; goosegrass, Eleusine indica (L.) Gaertn. ELEIN; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. IPOHE; jimsonweed, Datura stramonium L. DATST; large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA; pitted morningglory, Ipomoea lacunosa L. IPOLA; prickly sida, Sida spinosa L. SIDSP; sicklepod, Senna obtusifolia (L.) Irwin and Barnaby CASOB; smooth pigweed, Amaranthus hybridus L. AMACH; tall morningglory, Ipomoea purpurea L. PHBPU; velvetleaf, Abutilon theophrasti Medicus ABUTH; cotton, Gossypium hirsutum L. ‘Paymaster 1330RR’, ‘Stoneville BXN47’, ‘Stoneville 474’.

Diclosulam Does Not Influence Yields in Eight Virginia Market-Type Peanut (Arachis hypogaea) Cultivars1

Abstract: Field studies were conducted in 1996 and 1997 to evaluate response of eight peanut cultivars to flumioxazin applied preemergence (PRE) at 71 g ai/ha. Peanut cultivars evaluated include ‘NC 12C’, ‘NC 7’, ‘VAC 92R’, ‘NC-V 11’, ‘NC 10C’, ‘AT VC 1’, ‘NC 9’, and the experimental breeding line ‘N9001OE’. Visible injury 3 wk after planting in 1996 was 3% or less regardless of cultivar. In 1997, all cultivars were injured 15 to 28% with flumioxazin PRE, except VC 1, which was injured 45%. No visible injury was observed at 5 and 9 wk after planting. Flumioxazin did not influence the incidence of early leaf spot, late leaf spot, southern stem rot, cylindrocladium black rot, or tomato spotted wilt virus. Flumioxazin did not affect percentage of extra-large kernels, sound mature kernels, other kernels, and total yield. Nomenclature: Flumioxazin; peanut, Arachis hypogaea L., ‘NC 12C’, ‘NC 7’, ‘VAC 92R’, ‘NC-V 11’, ‘NC 10C’, ‘AT VC 1’, ‘NC 9’, ‘N9001OE’. Additional index words: Disease interaction, Cylindrocladium crotalariae (Loos) Bell and Sobers, Cercospora arachidicola Hori, Cercosporidium personatum (Berk. and Curt.), Sclerotium rolfsii Sacc., grade parameters, extra-large kernels, sound mature kernels, sound splits, total kernels, other kernels, fancy pods. Abbreviations: CBR, cylindrocladium black rot; DAP, days after planting; ELK, extra-large kernels; PPI, preplant incorporated; PRE, preemergence; SMK, sound mature kernels; SS, sound splits; TMSK, total sound mature kernels; TSWV, tomato spotted wilt virus; WAP, weeks after planting.

Weed Control and Snap Bean (Phaseolus vulgaris) Response to Reduced Rates of Fomesafen1

Abstract: Field studies were conducted in 1996 and 1997 to evaluate response of eight peanut cultivars to diclosulam applied preplant incorporated at 36 g ai/ha in a weed-free environment. Peanut cultivars evaluated included ‘NC 12C’, ‘NC 7’, ‘VAC 92R’, ‘NC-V 11’, ‘NC 10C’, ‘AT VC 1’,‘NC 9’, and the experimental breeding line N90010E. Visible injury 3 wk after planting was less than 5% regardless of cultivar. No injury was observed at 21 d after planting. Diclosulam did not influence the incidence of early leaf spot, late leaf spot, southern stem rot, cylindrocladium black rot, or tomato spotted wilt virus. Diclosulam did not affect percentage of extra large kernels, sound mature kernels, other kernels, and yield. Nomenclature: Diclosulam; peanut, Arachis hypogaea L. NC 12C, NC 7, VAC 92R, NC-V 11, NC 10C, AT VC 1, NC 9, N90010E. Additional index words: Disease interaction, cylindrocladium black rot, Cylindrocladium crotalariae (Loos) Bell et Sobers, early leaf spot, Cercospora arachidicola Hori, late leaf spot, Cercosporidium personatum (Berk. et Curt.), southern stem rot, Sclerotium rolfsii Sacc., tomato spotted wilt virus, grade parameters, extra large kernels, sound mature kernels, sound splits, total kernels, other kernels, fancy pods. Abbreviations: CBR, cylindrocladium black rot; DAP, days after planting; ELK, extra large kernels; PPI, preplant incorporated; SMK, sound mature kernels; SS, sound splits; TSMK, total sound mature kernels; TSWV, tomato spotted wilt virus; WAP, weeks after planting.

Herbicide Effects on Visible Injury, Leaf Area, and Yield of Glyphosate-Resistant Soybean (Glycine max)1

Field experiments were conducted in 1996, 1999, and 2000 to evaluate weed control and snap bean response to postemergence applications of fomesafen at registered and reduced rates. S-Metolachlor was applied preemergence to all plots to suppress annual grasses. Snap bean injury generally increased as fomesafen rate increased, but at rates up to 0.28 kg ai/ha, injury by fomesafen was similar to or less than that from bentazon. Fomesafen at rates as low as 0.07 kg/ha provided near-complete control of common ragweed, and rates of 0.14 kg/ha or more of fomesafen controlled ivyleaf and pitted morningglories and 5-cm or smaller common lambsquarters as effectively as did bentazon. Control of all weed species from fomesafen alone at 0.21 kg/ha did not improve with the addition of bentazon at 0.28 kg/ha. Although snap bean injury from fomesafen was as high as 43% 1 wk after treatment, snap bean yield and net returns were similar to those from S-metolachlor alone. In a rate and application timing study, fomesafen at 0.14 kg/ha applied to three-trifoliolate snap bean was the least injurious to the crop, whereas applications at 0.28 kg/ha to one- or two-trifoliolate snap bean provided the best weed control. Nomenclature: Bentazon; fomesafen; S-metolachlor; common lambsquarters, Chenopodium album L. #3 CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE; pitted morningglory, Ipomoea lacunosa L. # IPOLA; snap bean, Phaseolus vulgaris L. ‘Bronco’, ‘Gator Green’. Additional index words: Fomesafen linear effect, snap bean yield, net returns. Abbreviations: fb, followed by; POST, postemergence; PRE, preemergence; WAT, weeks after treatment.

Influence of Cultivation and Herbicide Programs on Weed Control and Net Returns in Potato (Solanum tuberosum)1

The failure of glyphosate to control all weeds throughout the entire growing season has sometimes prompted growers to use herbicides other than glyphosate on glyphosate-resistant soybean. Field studies were conducted in 1999 and 2000 to investigate potential crop injury by several herbicides in glyphosate-resistant soybean and to determine the relationships between soybean maturity group, planting date, and herbicide treatment on soybean injury, leaf area index (LAI), and yield. Glyphosate-resistant soybean generally recovered from early-season herbicide injury and LAI reductions; however, some treatments reduced yield. Yield reductions were more common in double-crop soybean than in full-season soybean. In full-season soybean, most yield reductions occurred in the early-maturing ‘RT-386’ cultivar. These yield reductions may be attributed to reduced developmental periods associated with early-maturing cultivars and double-crop soybean that often lead to reduced vegetative growth and limited LAI. Reductions in LAI by some herbicide treatments were not necessarily indicative of yield loss. Further yield reductions associated with herbicide applications occurred, although soybean sometimes produced leaf area exceeding the critical LAI level of 3.5 to 4.0, which is the minimum LAI needed for soybean to achieve maximum yield. Therefore, LAI response to herbicide treatments does not always accurately indicate the response of glyphosate-resistant soybean yield to herbicides. Nomenclature: Glyphosate; soybean, Glycine max (L.) Merr. Additional index words: Double-crop soybean, full-season soybean, soybean maturity group. Abbreviations: EPSPS, 5-enolpyruvylshikimate-3-phosphate synthase (EC 2.5.1.19); fb, followed by; LAI, leaf area index; PRE, preemergence; POST, postemergence; WAP, weeks after planting.

Diclosulam Systems for Weed Management in Peanut (Arachis hypogaea L.) 1

Field studies were conducted near Painter, VA, in 1995 and 1996 to investigate the effects of herbicides and cultivation on weed control, yield, and net returns in potato. Potato injury from herbicides and/or cultivation was not observed in 1995 and was less than 12% in 1996. Metribuzin plus metolachlor preemergence controlled yellow nutsedge by at least 81% regardless of the number of cultivations in 1995 and 1996. Yellow nutsedge control with metribuzin plus rimsulfuron postemergence (POST) plus three cultivations was as high as 70% in 1995 and 88% in 1996. Metribuzin plus rimsulfuron POST controlled common lambsquarters by at least 95% and common ragweed by at least 83% regardless of the number of cultivations in 1995 and 1996. A-size tuber production and net returns from potato receiving herbicides were not improved with two or three cultivations in 1995 or 1996. However, when averaged over all weed control systems (herbicide and cultivation-only systems) multiple cultivations significantly increased control of all weed species, A-size tuber production, and net returns. Nomenclature: Metolachlor; metribuzin; rimsulfuron; common lambsquarters, Chenopodium album L. #3 CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; potato, Solanum tuberosum L., ‘Superior’; yellow nutsedge, Cyperus esculentus L. # CYPES. Additional index word: A-size potato. Abbreviations: POST, postemergence; PRE, preemergence; WAP, weeks after planting; WAT, weeks after treatment.

Weed Management, Fiber Quality, and Net Returns in No-Tillage Transgenic and Nontransgenic Cotton (Gossypium hirsutum)1

Abstract: Field studies were conducted at Lewiston and Rocky Mount, NC, in 1996 and 1997 to evaluate weed control and peanut response to preplant incorporated (PPI) treatments of diclosulam alone and in systems with postemergence (POST) commercial standard herbicides. All plots received ethalfluralin PPI at 840 g ai/ha. In both years, ethalfluralin plus diclosulam PPI at 17 or 26 g ai/ha followed by (fb) acifluorfen plus bentazon POST, paraquat plus bentazon POST, or imazapic POST controlled common lambsquarters, ivyleaf morningglory, pitted morningglory, prickly sida, smooth pigweed, spurred anoda, and yellow nutsedge in a manner similar to or better than did the commercial standards of ethalfluralin PPI fb metolachlor preemergence (PRE) fb acifluorfen plus bentazon or ethalfluralin PPI fb acifluorfen plus bentazon POST. Yield from peanut treated with diclosulam systems that included POST herbicides was equivalent to or higher than that from peanut treated with ethalfluralin PPI fb metolachlor PRE fb acifluorfen plus bentazon POST or ethalfluralin PPI fb acifluorfen plus bentazon POST. Peanut exhibited excellent tolerance to diclosulam PPI at all rates. Nomenclature: Acifluorfen; bentazon; diclosulam; ethalfluralin; imazapic; metolachlor; paraquat; common lambsquarters, Chenopodium album L. #3 CHEAL; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE; pitted morningglory, Ipomoea lacunosa L. # IPOLA; prickly sida, Sida spinosa L. # SIDSP; smooth pigweed, Amaranthus hybridus L. # AMACH; spurred anoda, Anoda cristata (L.) Schlecht. # ANVCR; yellow nutsedge, Cyperus esculentus L. # CYPES; peanut, Arachis hypogaea L. ‘NC 7’, ‘NC 10C’. Additional index words: Herbicide injury. Abbreviations: fb, followed by; POST, postemergence; PPI, preplant incorporated; PRE, preemergence.

Tolerance of Imidazolinone-Resistant Corn (Zea mays) to Diclosulam1

Studies on weed management systems with bromoxynil-resistant, glyphosate-resistant, and nontransgenic cotton cultivars in a no-tillage environment were evaluated in North Carolina and Tennessee in 1997 and 1998. All weed management systems in nontransgenic and bromoxynil-resistant cotton controlled sicklepod 72 to 78%, whereas sicklepod was controlled at least 94% in glyphosate-resistant cotton. Entireleaf and pitted morningglory, smooth pigweed, and common cocklebur were controlled at least 92% with all management systems. Fiber quality was also measured in Tennessee. Micronaire and fiber strength ranged from 4.35 to 4.55 units and 28.6 to 30.1 g/tex, respectively, in bromoxynil-resistant and glyphosate-resistant cultivars that received postemergence over-the-top (POT) herbicides. Harvest trash content ranged from 0.80 to 1.15% in systems where POT and late postemergence–directed (LAYBY) herbicides were used and was 1.65% where multiple glyphosate applications were used with no LAYBY herbicides. Cotton lint yield and net returns were generally highest in systems that included bromoxynil or pyrithiobac POT followed by cyanazine plus MSMA LAYBY or multiple glyphosate treatments where no LAYBY herbicides were used. Nomenclature: Bromoxynil; cyanazine; glyphosate; MSMA; pyrithiobac; common cocklebur, Xanthium strumarium L. #3 XANST; entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray # IPOHG; pitted morningglory, Ipomoea lacunosa L. # IPOLA; sicklepod, Senna obtusifolia (L.) Irwin and Barnaby # CASOB; smooth pigweed, Amaranthus hybridus L. # AMACH; cotton, Gossypium hirsutum L. ‘Stoneville 474’, ‘Stoneville BXN 47’, ‘Deltapine 5415RR’, ‘Paymaster 1220RR’. Additional index words: Color grade, extraneous material, fiber length, fiber strength, fiber uniformity, harvest trash, high-volume instrumentation, gin turn out, leaf grade, micronaire, staple length. Abbreviations: ASN, as needed; LAYBY, late postemergence–directed; fb; followed by; PDS, postemergence-directed spray; PRE, preemergence; POT, postemergence over-the-top.

Responses of Selected Weeds and Glyphosate-Resistant Cotton and Soybean to Two Glyphosate Salts1

Field experiments were conducted in 1996 and 1997 to evaluate the tolerance of imidazolinone-resistant (IR) and non-IR corn cultivars to preemergence (PRE) and postemergence (POST) treatments of diclosulam. Crop injury was evaluated early- (5 to 6 wk after planting [WAP]), mid- (10 to 11 WAP), and late-season (13 to 15 WAP). Early-season injury of IR corn was no more than 12% in systems that included diclosulam PRE or POST at 18, 27, or 36 g ai/ha. Early-season injury of non-IR corn ranged from 85 to 89% in systems that included diclosulam PRE at any rate. At the mid-season evaluation, crop injury to IR corn was 1% or less. Non-IR corn was injured 73 to 94% in systems that included diclosulam PRE, while systems that included diclosulam POST caused 45 to 58% injury at mid-season. At the late-season evaluation, non-IR corn was injured 56, 88, and 96% with diclosulam PRE at 18, 27, and 36 g/ha, respectively, whereas systems that included diclosulam POST had 11 to 14% injury. Injury to IR corn from diclosulam PRE or POST was not apparent at the late-season evaluation. Weed-free yield of IR corn treated with diclosulam was 6,490 to 6,850 kg/ha and was equivalent to or better than yield from IR corn treated only with atrazine plus metolachlor PRE. Yield from non-IR corn treated with any diclosulam-containing system did not exceed 3,770 kg/ha. Nomenclature: Atrazine; diclosulam; metolachlor; corn, Zea mays L. ‘Pioneer 3242’, ‘Pioneer 3223’. Additional index words: Crop injury, crop tolerance, discoloration, stand reduction, stunting. Abbreviations: ALS, acetolactate synthase [EC 4.1.3.18]; IR, imidazolinone-resistant; POST, postemergence; PRE, preemergence; WAP, weeks after planting.