Robert J. Richardson

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.

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.

Aquatic Plant Management and The Impact of Emerging Herbicide Resistance Issues

Aquatic plants provide many benefits to the environment, but must be managed when growth reaches nuisance levels or when invasive plant species are released. Management tactics include biological, chemical, cultural, mechanical, and physical tools. Each specific management technique has advantages and disadvantages. In addition, the implementation of these techniques can become complicated because of the multiple users, managers, and stakeholders that may be present on large bodies of water. As an example, hydrilla is the most economically damaging aquatic weed in the United States. It reproduces through fragmentation, turions, and occasionally seed and can colonize a wide variety of aquatic environments. The most common management tactics for hydrilla include biological, chemical, and mechanical tools. Triploid grass carp have been the primary biological control agent, whereas fluridone has been the only systemic herbicide used. Because of heavy utilization of fluridone, biotypes have developed resistance to this herbicide in Florida. Although several acetolactate synthase-inhibiting herbicides are in development, herbicides with additional modes of action are needed for resistance management. Other aquatic plant management needs include additional control tactics for algae and additional extension resources for public education. Nomenclature: Fluridone, hydrilla, Hydrilla verticillata (L.f.) Royle, triploid grass carp, Ctenopharyngodon idella Val

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’

Mesotrione Combinations for Postemergence Control of Horsenettle (Solanum carolinense) in Corn (Zea mays)

Field and greenhouse studies were conducted near Painter, VA, in 1999, 2000, and 2001 to evaluate mesotrione postemergence for control of horsenettle in corn. Mesotrione at 105 g ai/ha controlled horsenettle at least 80% in all studies, and in 2001, after two consecutive annual applications, mesotrione controlled horsenettle up to 91%. Additions of primisulfuron, dicamba, and 2,4-D to mesotrione did not increase horsenettle control. Occasionally, combinations of dicamba with mesotrione controlled horsenettle less than did mesotrione alone, and primisulfuron combinations with mesotrione delayed or reduced development of bleaching symptoms associated with mesotrione. Initial horsenettle response to mesotrione was increased by addition of 280 g ai/ha atrazine; however, late-season horsenettle control was not improved by atrazine. Two consecutive annual applications of mesotrione alone decreased horsenettle biomass > 89%. Treatments of primisulfuron plus dicamba, primisulfuron plus CGA 152005 plus dicamba, and 2,4-D plus dicamba provided similar horsenettle control and biomass reductions as did 105 g/ha mesotrione alone. Nomenclature: Atrazine; CGA 152005 [1-(4-methoxy-6-methyl-triazin-2-yl)-3-[2-(3,3,3-trifluoropropyl)-phenylsulfonyl]-urea]; dicamba; halosulfuron; mesotrione; primisulfuron; 2,4-D; horsenettle, Solanum carolinense L. #3 SOLCA; corn, Zea mays L. Additional index words: Bleaching herbicides, perennial weeds, triketone herbicides. Abbreviations: COC, crop oil concentrate; POST, postemergence; PRE, preemergence; UAN, urea ammonium nitrate; WAT, weeks after treatment; YAT, years after treatment.

Influence of Adjuvants on Cotton (Gossypium hirsutum) Response to Postemergence Applications of CGA 3626221

Studies were conducted in 1999, 2000, and 2001 to evaluate cotton response to CGA 362622 applied postemergence with various adjuvants. In field studies, CGA 362622 was applied at 3.8 or 7.5 g ai/ha with nonionic surfactant, crop-oil concentrate (COC), or a urea-based adjuvant. A nontreated control was maintained weed free for comparison. Crop injury over all years at 1 wk after treatment (WAT) was 27 and 34% from 3.8 and 7.5 g/ha CGA 362622, respectively, when rates were pooled over adjuvants. At 4 WAT, injury was 6 to 14% with 3.8 g/ha and 10 to 21% with 7.5 g/ha CGA 362622 during the 3-yr study. Cotton heights at 2 WAT were reduced by 16 to 31% of nontreated cotton heights by CGA 362622. Heights of treated cotton did not differ and were generally equivalent to the nontreated control at 8 WAT. Cotton injury and height reduction were greatest when CGA 362622 was applied with COC. Cotton lint yields and fiber quality were not affected by CGA 362622 rate or adjuvant treatment. Cotton injury from CGA 362622 in the greenhouse was similar to that in the field. Initial cotton injury and subsequent reduction in leaf area or shoot dry weight were generally lowest when CGA 362622 was applied with no adjuvant or UBA in the greenhouse. 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; cotton, Gossypium hirsutum L. ‘SureGrow 125.’ Additional index words: Sulfonylurea herbicide. Abbreviations: ALS, acetolactate synthase enzyme (EC 4.1.3.18); COC, crop oil concentrate; MSO, methylated seed oil; NA, no adjuvant; NIS, nonionic surfactant; OSS, organosilicone surfactant; POST, postemergence; UBA, urea-based adjuvant; WAT, weeks after treatment.

Absorption, Translocation, and Metabolism of Aminocyclopyrachlor in Tall Fescue (Lolium arundinaceum)

Abstract Synthetic auxin herbicides are commonly used in forage, pasture, range, and turfgrass settings for dicotyledonous weed control. Aminocyclopyrachlor (AMCP) is a newly developed pyrimidine carboxylic acid with a chemical structure and mode of action similar to the pyridine carboxylic acids—aminopyralid, clopyralid, and picloram. Injury to sensitive dicotyledonous plants has been observed following exposure to monocotyledonous plant material previously treated with pyridine compounds. The absorption, translocation, and metabolism of AMCP has been documented in susceptible broadleaf weeds; however, no information is available, to our knowledge, regarding AMCP fate in tolerant Poaceae, which may serve as the vector for off-target plant injury. Based on this premise, research was conducted to characterize absorption, translocation, and metabolism of AMCP in tall fescue. 14C-AMCP was applied to single tiller tall fescue plant foliage under controlled laboratory conditions at North Carolina State University (Raleigh, NC). Radiation was quantified in leaf wash, treated leaf, foliage, crown, roots, and root exudates at 3, 12, 24, 48, 96, and 192 h after treatment (HAT). 14C-AMCP was rapidly absorbed by tall fescue, reaching 38 and 68% at 3 and 48 HAT, respectively. Translocation of 14C-AMCP was limited to the foliage, which reached maximum translocation (34%) at 96 HAT. Most of the recovered 14C-AMCP remained in the leaf wash, treated leaf, or foliage, whereas minimal radiation was detected in the crown, roots, or root exudates throughout the 192-h period. No AMCP metabolism was observed in tall fescue through the 192 HAT. These data suggest AMCP applied to tall fescue can remain bioavailable, and mishandling treated plant material could result in off-target injury. Nomenclature: Aminocyclopyrachlor; tall fescue, Lolium arundinaceum (Schreb.) S.J. Darbyshire.

Strategies for Control of Horseweed (Conyza canadensis) and Other Winter Annual Weeds in No-Till Corn

Abstract Field studies were conducted to determine if mesotrione alone or in combinations with other corn herbicides would control horseweed and other winter annual weeds associated with no-till corn. Mesotrione alone controlled horseweed 52 to 80% by 3 wk after treatment (WAT); however, by 7 WAT control diminished to between 37 to 68%, depending on mesotrione rate. Mesotrione at 0.16 kg ai/ha plus atrazine at 0.28 kg ai/ha controlled 99% of horseweed and annual bluegrass and 88% of yellow woodsorrel. Combinations of mesotrione at 0.16 kg/ha plus acetochlor at 1.79 kg ai/ha plus 1.12 kg ai/ha glyphosate (trimethylsulfonium salt of glyphosate) or 0.7 kg ai/ha paraquat provided 93% or greater control of all three weed species. Glyphosate alone also controlled all weed species 97 to 99%, while paraquat alone provided 99% control of annual bluegrass, 72% control of horseweed, and 36% control of yellow woodsorrel. Mixtures of paraquat plus acetochlor improved control of horseweed (93%) and yellow woodsorrel (73%) over control with either herbicide applied alone. Nomenclature: Acetochlor; atrazine; glyphosate-Tms (trimethylsulfonium salt); mesotrione; paraquat; annual bluegrass, Poa annua L. POAAN; horseweed, Conyza canadensis (L.) Cronq. ERICA; yellow woodsorrel, Oxalis stricta L. OXAST; corn, Zea mays L.

Mesotrione Combinations with Atrazine and Bentazon for Yellow and Purple Nutsedge (Cyperus Esculentus and C. Rotundus) Control in Corn

Field and greenhouse studies were conducted to evaluate mesotrione alone and in combinations with low rates of atrazine and bentazon for control of yellow and purple nutsedge. Mesotrione alone at rates of 105 to 210 g ai/ha controlled yellow nutsedge 43 to 70%. Mixtures of mesotrione with atrazine at 280 g ai/ha did not always improve yellow nutsedge control over that by mesotrione alone, but increasing atrazine to 560 g ai/ha in these mixtures generally provided more consistent control of yellow nutsedge. Mesotrione at 105 g ai/ha mixed with bentazon at 280 or 560 g ai/ha controlled yellow nutsedge 88% or greater which was similar to control from the standard halosulfuron at 36 g ai/ha. Mesotrione, atrazine, and bentazon alone did not control purple nutsedge. Mixtures of mesotrione plus bentazon, however, did improve control of purple nutsedge over either herbicide applied alone, but this control was not considered commercially acceptable. Nomenclature: Atrazine; bentazon; halosulfuron; mesotrione; yellow nutsedge, Cyperus esculentus L. CYPES; purple nutsedge, Cyperus rotundus L. CYPRO; corn,Zea mays L