Evaluation of Glufosinate-Tolerant Cotton and the Effects of Cotton Cultivar Development on Boll Distribution

Glyphosate resistant (GR) weed biotypes, especially Palmer amaranth ( Amaranthus palmeri S. Watson) and Giant ragweed (Ambrosia trifida L.) have caused shifts in postemergence (POST) and preemergence (PRE) herbicide use programs. Greenhouse and field experiments were conducted in 2013 and 2014 to determine the effects of POST herbicides, chloroacetamide herbicides, acephate, and tank mix combinations of these pesticides on cotton (Gossypium hirsutum L.) cultivar FM1944GLB2, thrips ( Frankliniella spp.) control, and weed control. Cotton injury from either POST herbicides or chloroacetamide herbicides were reduced 8 to 20% by acephate in both greenhouse and field experiments. Cotton biomass in greenhouse trials and lint yields in field experiments were not affected by any herbicide treatment. Interactions of these pesticides were not observed for control of Palmer amaranth, entireleaf morningglory (Ipomoea hederacea Jacq.), large crabgrass (Digitaria sanguinalis L.) and common ragweed (Ambrosia artemisiifolia L.).;The loss of aldicarb has caused a shift in thrips management in cotton. Neonicotinoid seed treatments are effective; however, 85% of cotton hectares in 2013 required a foliar insecticide application. Four field experiments were conducted to determine the effects of aldicarb, acephate and glufosinate plus acephate on thrips injury, plant heights, white flower production, lint yield and fiber quality with two cotton cultivars. Although thrips injury was not observed at any location, aldicarb increased plant heights 30-35 days after planting (DAP) at two of the four locations, while the acephate plus glufosinate applied early POST increased plant heights at one location. No cultivar and treatment interactions were observed on mid-season plant heights and white flower counts at early and late bloom. Treatments increased lint yields an average of 130 kg lint ha-1 at one of the four locations, while cultivar affected yield at two locations. ST4145LLB2 yielded 160 and 300 kg lint ha-1 more than FM1845LLB2 in 2012 and 2013, respectively.;Experiments at dryland and irrigated locations were conducted with two LibertyLink cotton cultivars to determine the effects of glufosinate on plant development and lint yield. Drought stressed cotton will have increased leaf cuticle thickness and increased total wax content which may affect responses to POST herbicides. Applications of glufosinate at early, mid and late POST emergent did not affect plant heights or white flower counts. Irrigated locations yielded 19% and 21% more than the dryland locations in 2011 and 2012, respectively. Glufosinate did not affect lint yield or fiber quality.;Field experiments were conducted at high and normal soil-available nitrogen locations to compare first position boll weights and subtending leaf dry weights for the 7th, 9th, 11th and 13 th sympodial node with modern and obsolete cotton cultivars. Cultivar effected seedcotton weights from the first fruiting site on the 7th sympodial node and lint yield on the 13th sympodial node; however, these effects did not correlate with cultivar release date. Regressional analyses of lint percentage from the 9th and 13 th node versus cultivar release date resulted in r2 values of 0.60 and 0.36, respectively. Soil-available nitrogen affected subtending leaf dry weights, but cultivar did not.