Thomas E. Hines

Mesotrione combinations in no-till corn (Zea mays)

Field studies were conducted in 1999, 2000, and 2001 to determine the effectiveness of mesotrione applied preemergence (PRE) or postemergence (POST) in no-till corn. Also, a proposed prepackage mix of mesotrione plus acetochlor (1:11 ratio of mesotrione–acetochlor) in combinations with the trimethylsulfonium salt of glyphosate (glyphosate-TMS), paraquat, and 2,4-D was investigated. Mesotrione PRE at 235 g ai/ha or greater controlled common lambsquarters, smooth pigweed, and common ragweed at least 80%. POST mesotrione at 35 g/ha and higher controlled common lambsquarters 91% or greater. Mesotrione applied POST at 140 g/ha controlled smooth pigweed greater than 97%. Common ragweed control from POST mesotrione was inconsistent, ranging from 56 to 97%. PRE and POST applications of mesotrione did not adequately control goosegrass, giant foxtail, fall panicum, johnsongrass, or cutleaf eveningprimrose. The mesotrione plus acetochlor prepackage mix plus glyphosate-TMS or paraquat controlled field pansy and ivyleaf morningglory similar to or better than did the prepackage mixture of the isopropylamine salt of glyphosate (glyphosate-IPA) plus atrazine plus acetochlor. But common ragweed control by mesotrione plus acetochlor plus glyphosate-TMS or paraquat was occasionally lower than control by the prepackage mixture of glyphosate-IPA plus atrazine plus acetochlor. Corn injury was generally less than 10% with PRE and POST mesotrione applications. Nomenclature: Acetochlor; atrazine; 2,4-D; glyphosate-Ipa (isopropylamine salt of glyphosate); glyphosate-TMS (trimethylsulfonium salt of glyphosate); mesotrione; paraquat; common lambsquarters, Chenopodium album L. #3 CHEAL; common ragweed, Ambrosia artemisiifolia L.# AMBEL; cutleaf eveningprimrose, Oenothera laciniata Hill # OEOLA; fall panicum, Panicum dichotomiflorum Michx. # PANDI; field pansy, Viola arvensis Murr. # VIOAR; giant foxtail, Setaria faberi Herrm. # SETFA; goosegrass, Eleusine indica (L.) Gaertn # ELEIN; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE; johnsongrass, Sorghum halepense (L.) Pers. # SORHA; smooth pigweed, Amaranthus hybridus L. # AMACH; corn, Zea mays L. Additional index words: Bleaching herbicides, burndown, nonselective herbicides, triketone herbicides. Abbreviations: COC, crop-oil concentrate; DAT, days after treatment; fb, followed by; PRE, preemergence; POST, postemergence; UAN, urea ammonium nitrate; WAT, weeks after treatment.

Glyphosate Interactions with Manganese

Abstract: Field experiments were conducted on the Eastern Shore of Virginia from 1999 to 2001 to evaluate the effects of tank mixture applications of isopropylamine or trimethylsulfonium salts of glyphosate with two liquid formulations of manganese (Mn lignin or Mn chelate) on spray solution pH and weed control in glyphosate-resistant soybean. Additions of manganese to herbicide solutions resulted in a reduction in the acidifying effects of the herbicides as well as in the control of common lambsquarters, large crabgrass, morningglory spp., and smooth pigweed. Reduced control caused by manganese could be overcome with higher rates of the herbicides on some species, but reduced control of common lambsquarters was seen when manganese was included with any herbicide application rate. For most species, Mn chelate caused a greater reduction in control than did Mn lignin. Although manganese caused significant decreases in weed control, soybean yield was not influenced by glyphosate salt, application rate, or manganese. Reduced weed control caused by the addition of manganese to herbicide solutions may be due to the complexing of the herbicide formulations, which could result in the formation of insoluble salt complexes that are not readily absorbed through the plant cuticle, resulting in decreased glyphosate phytotoxicity. Nomenclature: Glyphosate; common lambsquarters, Chenopodium album L. #3 CHEAL; large crabgrass, Digitaria sanguinalis L. # DIGSA; morningglory spp., Ipomoea spp. # IPOSS; smooth pigweed, Amaranthus hybridus L. # AMACH; soybean, Glycine max (L.) Merr. ‘Asgrow 5401 RR’. Additional index words: pH, reduced weed control, tank mixture. Abbreviations: Ipa, isopropylamine; POST, postemergence; Tms, trimethylsulfonium; WAP, weeks after planting; WAT, weeks after treatment.

Mesotrione, Acetochlor, and Atrazine for Weed Management in Corn (Zea mays)1

Field studies were conducted in 1999, 2000, and 2001 to investigate weed control and crop safety with preemergence (PRE) and postemergence (POST) applications of mesotrione alone and in tank mixtures with acetochlor and atrazine. Corn injury was less than 4% with all mesotrione treatments in 1999 and 2001, but it was 8 to 20% in 2000, when rainfall was 3.1 cm 7 d after PRE applications. Mesotrione PRE at 0.16 and 0.24 kg ai/ha did not adequately control most broadleaf weeds or giant foxtail. Tank mixtures of mesotrione plus acetochlor controlled smooth pigweed and giant foxtail but did not adequately control common ragweed, common lambsquarters, or morningglory species. Control by tank mixtures of mesotrione plus atrazine at 0.56 kg ai/ha was frequently low and varied with rainfall after PRE applications. All weed species were controlled 80% or more by mesotrione plus acetochlor PRE or atrazine plus acetochlor PRE followed by mesotrione POST at 0.11 kg/ha. Nomenclature: Acetochlor; atrazine; mesotrione; common lambsquarters, Chenopodium album L. #3 CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; giant foxtail, Setaria faberi Herrm. # SETFA; morningglory species, Ipomoea spp. # IPOSS; smooth pigweed, Amaranthus hybridus L. # AMACH; corn, Zea mays L. Additional index words: HPPD-inhibiting herbicides, triketone herbicides. Abbreviations: COC, crop oil concentrate; DAT, days after treatment; fb, followed by; POST, postemergence; PRE, preemergence; UAN, urea ammonium nitrate; WAT, weeks after treatment.

Mesotrione Alone and in Mixtures with Glyphosate in Glyphosate-Resistant Corn (Zea mays)1

Field studies were conducted in 1999, 2000, and 2001 to investigate weed control and glyphosate-resistant corn tolerance to postemergence applications of mesotrione at 70, 105, and 140 g ai/ha applied with and without glyphosate at 560 g ai/ha. Mesotrione alone and mixed with glyphosate controlled smooth pigweed greater than 97% and common lambsquarters 93 to 99%. Control of common ragweed and morningglory species was variable. Common ragweed control was generally best when mesotrione was applied at 105 or 140 g/ha, and control increased only in 2000 with the addition of glyphosate. Giant foxtail control was below 25% with all rates of mesotrione, but mixtures of mesotrione plus glyphosate controlled giant foxtail 65 to 75%. Mesotrione injured glyphosate-resistant corn 4 to 24% when averaged over glyphosate rates, and injury was usually increased by higher mesotrione rates, with rainfall after herbicide applications, and in mixtures with glyphosate. Injury was transient and did not reduce corn yields. Mesotrione injury on glyphosate-resistant corn was confirmed in the greenhouse, where all mesotrione treatments reduced glyphosate-resistant corn biomass 9 to 23% compared with the nontreated check. Nomenclature: Glyphosate; mesotrione; common lambsquarters, Chenopodium album L. #3 CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; giant foxtail, Setaria faberi Herrm. # SETFA; morningglory species, Ipomoea spp. # IPOSS; smooth pigweed, Amaranthus hybridus L. # AMACH; corn, Zea mays L. ‘Dekalb 626RR’, ‘Dekalb 5863RR’. Additional index words: IPOHE, IPOLA, Ipomoea hederacea (L.) Jacq., Ipomoea lacunosa L., Ipomoea purpurea L. Roth, IPOPU, total postemergence, transgenic crops, triketone herbicide. Abbreviations: DAT, days after treatment; POST, postemergence; WAT, weeks after treatment.

Preemergence Herbicides Followed By Trifloxysulfuron Postemergence In Cotton

Field studies were conducted in 1999, 2000, and 2001 to evaluate weed control and cotton response from PRE herbicides followed by (fb) trifloxysulfuron POST. In the first study, trifloxysulfuron at 3.8, 7.5, or 15 g ai/ha was applied POST with or without pendimethalin at 690 g ai/ha applied PRE in a factorial treatment arrangement. Visible crop injury occurred after all trifloxysulfuron applications, but injury was not affected by application of pendimethalin PRE. Cotton injury was 19 to 22% 7 d after POST treatment (DAT) from trifloxysulfuron at 3.8 to 15 g/ha but was 5 to 12% 28 DAT. Trifloxysulfuron controlled smooth pigweed, common ragweed, and common cocklebur, but spurred anoda, large crabgrass, goosegrass, and stinkgrass were not controlled by trifloxysulfuron. Morningglory species (tall morningglory, ivyleaf morningglory, and pitted morningglory) control with trifloxysulfuron at 7.5 and 15 g/ha was at least 79%, whereas velvetleaf was controlled 66% over all years. In a second study, clomazone, pendimethalin, pendimethalin plus fluometuron, pyrithiobac, or flumioxazin were applied PRE fb 7.5 g/ha trifloxysulfuron POST. Cotton injury from PRE herbicides fb trifloxysulfuron was 13 to 39% 7 DAT. Spurred anoda control exceeded 54% only with treatments that included flumioxazin or pyrithiobac PRE. Common lambsquarters, common cocklebur, and morningglory species were controlled at least 75% with all treatments that included trifloxysulfuron POST, whereas pendimethalin and clomazone usually controlled annual grasses. In both studies, the application of pendimethalin PRE controlled annual grass species and improved control of smooth pigweed and common lambsquarters over that controlled by trifloxysulfuron POST without a PRE herbicide. Nomenclature:Clomazone, flumioxazin, fluometuron, pendimethalin, pyrithiobac, trifloxysulfuron, common cocklebur, Xanthium strumarium L. XANST, common lambsquarters, Chenopodium album L. CHEAL, common ragweed, Ambrosia artemisiifolia L AMBEL, goosegrass, Eleusine indica (L.) Gaertn. ELEIN, ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. IPOHE, large crabgrass Digitaria sanguinalis (L.) Scop DIGSA, pitted morningglory, Ipomoea lacunosa L. IPOLA, smooth pigweed, Amaranthus hybridus L. AMACH, spurred anoda, Anoda cristata (L.) Schlecht. ANVCR, stinkgrass, Eragrostis megastachya (Koel.) Link, tall morningglory, Ipomoea purpurea (L.) Roth IPOPU, velvetleaf, Abutilon theophrasti Medicus ABUTH, cotton, Gossypium hirsutum L. ‘SG 125’

Comparison of Mesotrione Combinations with Standard Weed Control Programs in Corn1

Field experiments were conducted in 2002 and 2003 to evaluate total POST weed control in corn with mixtures of mesotrione, atrazine, and the commercial mixture of nicosulfuron plus rimsulfuron plus atrazine at registered and reduced rates. Treatments were compared with nicosulfuron plus rimsulfuron plus atrazine POST, and S-metolachlor plus atrazine PRE alone and followed by (fb) nicosulfuron plus rimsulfuron plus atrazine POST. All treatments controlled common lambsquarters 8 wk after the postemergence treatments (WAPT). Common ragweed control with POST mesotrione plus nicosulfuron plus rimsulfuron plus atrazine combinations was greater than 89%. Mesotrione plus the registered rate of nicosulfuron plus rimsulfuron plus atrazine POST controlled common ragweed more effectively than the PRE treatment alone. Addition of atrazine to mesotrione improved common ragweed control by at least 38 percentage points over mesotrione alone. Nicosulfuron plus rimsulfuron plus atrazine at the registered rate and in mixtures with mesotrione controlled morningglory species (pitted and ivyleaf morningglory) 89 to 91%. Large crabgrass control varied between 2002 and 2003. In 2002, large crabgrass control was 58 to 76% with all POST treatments, but in 2003, nicosulfuron plus rimsulfuron plus atrazine POST alone controlled large crabgrass greater than 86%. Large crabgrass was more effectively controlled by treatments with S-metolachlor plus atrazine PRE than by the total POST treatments in 2002. Giant foxtail was controlled at least 97% with nicosulfuron plus rimsulfuron plus atrazine treatments. S-metolachlor plus atrazine PRE fb nicosulfuron plus rimsulfuron plus atrazine POST controlled all weed species greater than 85%. Corn yields by total POST treatment combinations of mesotrione plus either rate of nicosulfuron plus rimsulfuron plus atrazine were comparable to S-metolachlor plus atrazine PRE alone or fb nicosulfuron plus rimsulfuron plus atrazine POST. Nomenclature: Atrazine; mesotrione; nicosulfuron; rimsulfuron; S-metolachlor; common lambsquarters, Chenopodium album L. #3 CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; giant foxtail, Setaria faberi Herrm. # SETFA; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA; morningglory species, Ipomoea spp. # IPOSS; pitted morningglory, Ipomoea lacunosa (L.) Roth # IPOLA; corn, Zea mays L. ‘Dekalb DKC60-09 (RR2)’, ‘Pioneer 33B51’, ‘Pioneer 33G56’. Additional index words: Reduced herbicide rates, total postemergence, sulfonylurea herbicides, triketone herbicides. Abbreviations: DAP, days after planting; fb, followed by; WATP, weeks after treatment with POST herbicides.

Mixtures of Glyphosate with CGA 362622 for Weed Control in Glyphosate-Resistant Cotton (Gossypium hirsutum)1

Field studies were conducted in 1999, 2000, and 2001 to evaluate broadleaf weed control in glyphosate-resistant cotton by glyphosate plus CGA 362622 applied postemergence. Treatments included 560 and 1,120 g ai/ha glyphosate-isopropylamine alone or in mixtures with CGA 362622 at 3.8 and 7.5 g ai/ha, and CGA 362622 at 7.5 g/ha alone. Cotton injury 7 d after treatment (DAT) was 3 to 11% from glyphosate alone and 16 to 24% from glyphosate plus CGA 362622. Injury 28 DAT with CGA 362622 or herbicide mixtures did not exceed 6%. Broadleaf weed control by herbicide mixtures was generally more consistent than control from either herbicide applied alone. Glyphosate plus CGA 362622 controlled common cocklebur and smooth pigweed better than glyphosate alone. In most instances, the mixtures also controlled common ragweed, common lambsquarters, ivyleaf morningglory, pitted morningglory, and tall morningglory better than glyphosate applied alone. Common cocklebur and smooth pigweed were controlled at least 85% by all treatments. CGA 362622 did not control spurred anoda or jimsonweed. Cotton yields generally reflected weed control. According to these results, glyphosate plus CGA 362622 mixtures can consistently control many broadleaf weeds in cotton. Nomenclature: CGA 362622 (proposed common name trifloxysulfuron sodium), N-[(4,6-dimethoxy- 2-pyrimidinyl)carbamoyl]-3-(2,2,2-trifluoroethoxy)-pyridin-2-sulfonamide sodium salt; glyphosate; common cocklebur, Xanthium strumarium L. #3 XANST; common lambsquarters, Chenopodium album L. # CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE; jimsonweed, Datura stramonium L. # DATST; pitted morningglory, Ipomoea lacunosa L. # IPOLA; smooth pigweed, Amaranthus hybridus L. # AMACH; spurred anoda, Anoda cristata (L.) Schlecht. # ANVCR; tall morningglory, Ipomoea purpurea (L.) Roth # IPOPU; cotton, Gossypium hirsutum L. ‘PM 1220 RR’, ‘PM 1218 BG/RR’, ‘SG 521 RR’. Additional index words: Herbicide mixtures, morningglory species. Abbreviations: DAT, days after treatment; POSD, postemergence directed; POST, postemergence.

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

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.

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

Response of Potato (Solanum tuberosum) and Selected Weeds to Sulfentrazone1

Field experiments were conducted in 2000 and 2001 near Painter, VA, to evaluate the potential of sulfentrazone for use in potato. Sulfentrazone was applied at 0.11, 0.14, 0.21, and 0.28 kg ai/ha preemergence (PRE) alone or in combination with metolachlor or metribuzin, or at emergence (AT EMERG) of potato to simulate a delayed PRE application where the herbicide would come into contact with potato foliage. Potato injury from sulfentrazone PRE at rates of up to 0.21 kg/ha was generally similar to injury from metribuzin, metolachlor, or metribuzin plus metolachlor PRE. However, AT EMERG applications resulted in excessive injury that ranged from 60 to 86%. AT EMERG applications also caused decreased potato height and alterations in potato-flowering patterns. Sulfentrazone at either application timing controlled common lambsquarters at least 98% even at the lowest rates and was more effective than metribuzin or metolachlor alone. Higher rates of sulfentrazone (0.28 kg/ha) also controlled goosegrass and large crabgrass. However, sulfentrazone at 0.28 kg/ha controlled common ragweed only 58%. Total potato yield and grade with sulfentrazone PRE applications were similar to those of potato treated with metribuzin, metolachlor, or metribuzin plus metolachlor in both years. Potato injury from AT EMERG applications of sulfentrazone plus metolachlor decreased total potato yield and caused changes in the grade distribution of B-size, small A–size, and extra-large potato in 2000. Nomenclature: Metolachlor; metribuzin; sulfentrazone; common lambsquarters, Chenopodium album L. #3 CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; goosegrass, Eleusine indica (L.) Gaertn. # ELEIN; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA; potato, Solanum tuberosum L. ‘Superior’. Additional index words: Degree-days, potato flowering, potato injury, potato yield and grade, rainfall, sulfentrazone, weed control. Abbreviations: AT EMERG, at emergence; POST, postemergence; PRE, preemergence; protox, protoporphyrinogen oxidase; WAT, weeks after treatment.