Fluometuron

Abstract: An experiment conducted at three locations in North Carolina during 1996 and 1997 compared weed control and cotton (Gossypium hirsutumL.) yield, fiber quality, and net returns from glyphosate [N-(phosphonomethyl)glycine]-tolerant cotton treated with various glyphosate and traditional herbicide systems. The standard system of trifluralin [2,6d in i t ro N ,N d i p r opy l -4 ( t r i f luoromethy l ) benzenamine] preplant incorporated and f l u o m e t u r o n { N , N d i m e t h y l N ’ [ 3 (trifluoromethyl)phenyl]urea} preemergence followed by fluometuron plus MSMA (monosodium methanearsonate) postemergence directed 3 to 4 weeks after planting and cyanazine {2-[[4-chloro-6(e thy lamino) -1 ,3 ,5t r iaz in -2-y l ]amino] -2methylpropanenitrile} plus MSMA postemergence directed 6 to 7 weeks after planting controlled large crabgrass [Digitaria sanguinalis(L.) Scop.], common cocklebur (Xanthium strumarium L.), common lambsquarters (Chenopodium albumL.), common ragweed (Ambrosia artemisiifolia L.), Amaranthus species,Ipomoeaspecies, prickly sida ( Sida spinosa L.), and sicklepod [Senna obtusifolia(L.) Irwin and Barneby] at least 98% at late season. Weed control, cotton yield, and net returns were similar when pyrithiobac {2-chloro-6-[(4,6-dimethoxy-2pyrimidinyl)thio]benzoic acid, sodium salt} applied postemergence over-the-top was substituted for fluometuron plus MSMA postemergence directed. Glyphosate applied once did not adequately control most species, and cotton yield and net returns were less than with the standard system. However, weed control, cotton yield, and net returns in systems with glyphosate applied postemergence over-the-top 3 to 4 weeks after planting followed by glyphosate or cyanazine plus MSMA postemergence directed 6 to 7 weeks after planting were similar to those with the standard system. Three applications of glyphosate were no more effective than two. Trifluralin and fluometuron were of no benefit in systems with glyphosate applied twice or glyphosate followed by cyanazine plus MSMA. No treatment affected fiber quality. Soil-applied herbicides such as trifluralin and fluometuron are routinely used to control annual grass and broadleaf weeds in cotton (Wilcut et al., 1995). However, these and other soil-applied herbicides seldomadequatelycontrol weeds seasonlong (Batts and York, 1997; Buchanan, 1992; Culpepper and York, 1997). Consequently, postemergence herbicides are routinely used in conjunction with soil-applied herbicides (Buchanan, 1992). Various herbicides applied postemergence directed can be used to control weeds that escape earlier treatment if a height differential exists between cotton and weeds (Buchanan, 1992; Wilcut et al., 1997). However, growers prefer to apply herbicides postemergence over-the-top rather than postemergence directed, especially on small cotton (Wilcut et al., 1996). Several graminicides can be applied postemergence over-the-top to control grass weeds without adversely affecting cotton (Wilcut et al., 1995). Fluometuron and MSMA can be applied postemergence over-the-top to control broadleaf weeds. However, postemergence-directed application is generally recommended (York and Culpepper, 1998) because postemergence over-thetop application of these herbicides can injure cotton, delay maturity, and reduce yield (Byrd and York, 1987; Guthrie and York, 1989; Snipes and Byrd, 1994). Pyrithiobac was registered in 1996 for postemergence over-the-top application to cotton to control broadleaf weeds (Jordan et al., 1993d; Smith et al., 1997). Cotton is normally tolerant of pyrithiobac applied postemergence over-the-top (Jordan et al., 1993a; Culpepper and York, 1997). Pyrithiobac applied postemergence over-the-top controls many of the commonly occurring broadleaf weeds (Wilcut et al., 1995; York and Culpepper, 1998). However, there are some important broadleaf weeds not controlled by pyrithiobac such 176 JOURNAL OF COTTON SCIENCE, Volume 2, Issue 4, 1998 as common lambsquarters, common ragweed, prickly sida, and sicklepod (Culpepper and York, 1997; Jordan et al., 1993b). Hence, traditional soilapplied herbicides and late postemergence-directed herbicides are generally recommended in conjunction with pyrithiobac (Culpepper and York, 1997; Turner and Allison, 1997; York and Culpepper, 1998). Additionally, grass control by pyrithiobac is inadequate (Ferreira et al. 1995). Graminicides can be mixed with pyrithiobac but reduced grass control may be observed with these mixtures (Jordan et al., 1993c; Tredaway et al., 1998). Glyphosate is recognized as an effective and environmentally benign herbicide (Franz et al., 1997). In susceptible plants, glyphosate inhibits 5enolpyruvylshikimate-3-phosphate synthase (E.C. 2.5.1.19), thus limiting synthesis and regulation of the aromatic amino acids (Devine et al., 1993; Franz, 1985). Glyphosate-tolerant cotton was developed by insertion of a gene coding for express ion of glyphosate-tolerant 5enolpyruvylshikimate-3-phosphate synthase (Nida et al., 1996). Glyphosate can be applied postemergence over-the-top from emergence through the four-leaf stage of glyphosate-tolerant cotton (Welch et al., 1997). After the four-leaf stage, glyphosate must be applied as a directed spray to avoid potential fruit abortion (Kalaher et al., 1997). Glyphosate controls a broad spectrum of annual and perennial grasses, sedges, and broadleaf weeds (Wilcut et al., 1996) and may be a viable alternative to other commonly used herbicides now that glyphosate-tolerant cotton is commercially available. The objective of our research was to compare weed control, cotton yield, and net returns from conventionally tilled glyphosate-tolerant cotton treated with various glyphosate and standard herbicide systems. MATERIALS AND METHODS The experiment was conducted on the Cherry Farm Unit at Goldsboro, NC, in 1996 and on the Central Crops Research Station at Clayton, NC, in 1996 and 1997. Soil at Goldsboro was a Kinston loam (fine-loamy, siliceous, nonacid thermic Typic Fluvaquents) with 2.5% organic matter and pH 5.3. Soils at Clayton included a Goldsboro loamy sand (fine-loamy, siliceous, thermic Aquic Paleudults) with 2.1% organic matter and pH 6.0 in 1996 and a Dothan loamy sand (fine-loamy, siliceous, thermic Plinthic Paleudults) with 2.7% organic matter and pH 6.1 in 1997. Cultural practices, including fertilization, insect management, plant growth management, and defoliation, were standard for North Carolina. Cotton cv. Coker 312-1445RR and Paymaster 1220RR were planted in conventionally prepared seedbeds in 1996 and 1997, respectively. Planting dates were 3 and 9 May at Clayton and Goldsboro, respectively, in 1996 and 16 May 1997 at Clayton. Plots were four 91-cm rows by 11 m. The experimental design was a randomized complete block with treatments replicated four times. Treatments consisted of a factorial arrangement of four soil-applied and five postemergence herbicide options. Soil-applied herbicide options were no herbicide, trifluralin preplant incorporated at 0.6 kg a.i. ha , fluometuron preemergence at 1.4 kg a.i. ha, and trifluralin preplant incorporated plus fluometuron preemergence at 0.6 plus 1.4 kg ha. Trifluralin was incorporated with a powerdriven, vertical-action tiller at Clayton and with two passes of a field cultivator at Goldsboro. Postemergence herbicide options included the following: glyphosate (Roundup Ultra from Monsanto Co., St. Louis, MO) applied early postemergence over-the-top; glyphosate applied mid-postemergence directed; glyphosate applied early postemergence over-the-top and midpostemergence directed; glyphosate applied early postemergence over-the-top, mid-postemergence directed, and late postemergence directed; and glyphosate applied early postemergence over-thetop followed by cyanazine plus MSMA applied mid-postemergence directed. Glyphosate and cyanazine plus MSMA were applied at 0.56 kg a.i. ha and 1.1 plus 2.2 kg a.i. ha , respectively. The postemergence-directed herbicides were applied to the lower 5 to 7 cm of the cotton plants. In addition to treatments within the factorial, the experiment included herbicide systems with trifluralin preplant incorporated plus fluometuron preemergence at 0.6 plus 1.4 kg ha applied alone or in conjunction with the following: pyrithiobac early postemergence over-the-top followed by cyanazine plus MSMA mid-postemergence directed; fluometuron plus MSMA early postemergence directed followed by 177 CULPEPPER & YORK: WEED MANAGEMENT IN GLYPHOSATE-TOLERANT COTTON cyanazine plus MSMA mid-postemergence directed; and cyanazine plus MSMA midpostemergence directed. Pyrithiobac was applied at 0.07 kg a.i. ha, and fluometuron plus MSMA at 1.1 plus 2.2 kg ha was directed to the lower 3 to 5 cm of the cotton plants. A nontreated check also was included. Early postemergence over-the-top and postemergence-directed herbicides were applied 3 to 4 weeks after planting when cotton was 7 to 10 cm tall with two to three leaves. Midpostemergence-directed herbicides were applied 6 to 7 weeks after planting when cotton was 20 to 26 cm with seven to eight leaves. Late postemergencedirected herbicides were applied 10 to 11 weeks after planting when cotton was 60 to 70 cm tall and blooming. Weed species, densities in the nontreated checks, and sizes at time of postemergence herbicide applications are listed in Table 1. A nonionic surfactant (X-77 Spreader, alkylarylpolyoxyethylene glycols, free fatty acids, and isopropanol from Valent USA Corp., Walnut Creek, CA) at 0.25% (v v ) was included with all postemergence herbicides except glyphosate. Herbicides were broadcast, and plots were not cultivated. Soil-applied and postemergence overhe-top herbicides were applied using a CO 2pressurized backpack sprayer equipped with flat fan nozzles and calibrated to deliver 160 L ha -1 at 170 kPa. The postemergence-directed herbicides were applied using a CO2-pressurized backpack sprayer equipped with three equally spaced flat fan nozzles