Weed Management in Glufosinate-Tolerant Cotton (Gossypium hirsutum L.)

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Title: Weed Management in Glufosinate-Tolerant Cotton (Gossypium hirsutum L.)
Author: Gardner, Andrew Perry
Advisors: David L. Jordan, Committee Member
David W. Monks, Committee Member
Alan C. York, Committee Chair
Abstract: Glufosinate controls a broad spectrum of weeds. Control of grassy weeds, however, can sometimes be inadequate, especially when grasses are large or under dry conditions. In situations where less than adequate control of grasses by glufosinate alone might be anticipated, growers may consider mixing a postemergence graminicide with glufosinate. Most herbicides mixed with graminicides antagonize grass control. Research was conducted in North Carolina to determine the potential for antagonism with mixtures of glufosinate and four postemergence graminicides and to determine if antagonism could be alleviated by increasing the rate of graminicide in mixtures, by adding ammonium sulfate to mixtures, or by applying glufosinate and graminicides sequentially. Antagonism was noted on johnsongrass [Sorghum halepense (L.) Pers.] and mixtures of the annual grasses broadleaf signalgrass [Brachiaria platyphylla (Griseb.) Nash], fall panicum (Panicum dichotomiflorum Michx.), goosegrass [Eleusine indica (L.) Gaertn.], and large crabgrass [Digitaria sanguinalis (L.) Scop.] when glufosinate was mixed with clethodim, fluazifop-P, quizalofop-P, or sethoxydim. Antagonism was not alleviated by increasing the graminicide rate in the mixture by 50% or by including ammonium sulfate in the mixture. Antagonism was not observed when graminicides were applied 3 or more days before glufosinate or 5 or more days after glufosinate. Amaranthus spp. can also be difficult to control in glufosinate-resistant (GR) cotton (Gossypium hirsutum L.). A field experiment was conducted at six locations to determine the effect of residual herbicides and timing of the initial glufosinate application on control of annual grasses, Palmer amaranth (Amaranthus palmeri S.Wats.), and redroot pigweed (Amaranthus retroflexus L.) in GR cotton. Annual grasses included mixtures of large crabgrass [Digitaria sanguinalis (L.) Scop.], goosegrass [Eleusine indica (L.) Gaertn.], broadleaf signalgrass [Brachiaria platyphylla (Griseb.) Nash], and fall panicum (Panicum dichotomiflorum Michx.). Common lambsquarters (Chenopodium album L.) and mixtures of entireleaf morningglory (Ipomoea hederacea var. integriuscula Gray), pitted morningglory (Ipomoea lacunosa L.), and tall morningglory [Ipomoea purpurea (L.) Roth] were also present. Initial glufosinate application timings were early postemergence (EPOST) to 1- to 2-leaf cotton or mid-postemergence (MPOST) to 3- to 4-leaf cotton. Residual herbicides included fluometuron, fomesafen, pendimethalin, and pyrithiobac applied preemergence (PRE) and pyrithiobac mixed with glufosinate applied EPOST or MPOST. All treatments included glufosinate applied late postemergence (LPOST) to 6- to 7-leaf cotton followed by prometryn plus MSMA postemergence-directed. Weed control and cotton yield were generally greater with glufosinate applied EPOST. Preemergence herbicides increased control of annual grasses and Amaranthus spp. after glufosinate EPOST or MPOST at all locations and at most locations after LPOST application. Greater late-season annual grass and Amaranthus spp. control was noted at four and two locations, respectively, in systems with PRE herbicides. Differences among PRE herbicides were minor except that pyrithiobac was less effective on annual grasses. Pyrithiobac applied postemergence (POST) was less effective than PRE herbicides. Ipomoea spp. and common lambsquarters were controlled well by all herbicide systems regardless of PRE herbicides or pyrithiobac POST. The PRE herbicides increased cotton yield at four of six locations while pyrithiobac POST increased yield at only one location. The results indicate good control of annual grasses, Amaranthus spp., Ipomoea spp., and common lambsquarters can be obtained in GR cotton with herbicide systems that include PRE herbicides and well-timed glufosinate applications.
Date: 2006-07-12
Degree: MS
Discipline: Crop Science
URI: http://www.lib.ncsu.edu/resolver/1840.16/1883

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