Interference and control of sharppod morningglory (Ipomoea cordatotriloba dennstedt) in glyphosate-resistant cotton.
Steele, Gregory Lee
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Sharppod morningglory is a perennial vine commonly found infesting croplands in Texas and the southeastern United States. Previous research regarding morningglory competition and control primarily focused on annual Ipomoea. Interference, control, and herbicide translocation of sharppod morningglory could differ from that of other morningglories because of differences in growth and resource allocation. Therefore, field and laboratory experiments were conducted from 2001 to 2004 to: 1) determine the effects of seed-propagated and root-sprouted sharppod morningglory on cotton economic value, yield, harvest efficiency, and fiber quality; 2) evaluate sharppod morningglory control with cotton herbicides, and determine the effect of diuron rates on glyphosate absorption and translocation; and 3) assess the impact of cotton herbicide program and cotton-corn rotation on weed species composition over three years. A relatively large proportion of sharppod morningglory biomass was accumulated belowground during the first 8 wk of growth in the greenhouse. Consequently, up to 6 plants 10-m row-1 did not significantly reduce cotton lint yield. Sharppod morningglory density impacted color grade more than any other classification parameter. Through combined effects on yield and quality, cotton lint value was reduced by approximately 85% in the presence of 8 sharppod morningglory 10 m-1. Glyphosate alone did not completely control sharppod morningglory. The use of glufosinate, bromoxynil, or a combination of glyphosate plus diuron provided acceptable control. Sharppod morningglory absorbed up to 75% of glyphosate when applied alone, but most glyphosate was retained in treated leaves and did not translocate well. Diuron decreased absorption, increased leaf retention, and inhibited glyphosate translocation to roots. Rotation to corn and the use of preemergence herbicides in cotton improved control of grass and broadleaf weeds during the year of treatment. In the season following the 3-yr rotation, there were no lasting effects of crop rotation on density or control of grasses and broadleaves. However, hand-hoed and herbicide treated plots resulted in weed densities 2- to 3-fold lower than the untreated. Preemergence herbicides and/or crop rotation can reduce weed density and improve weed control, but these strategies must be employed long-term to reduce density of problematic weeds through depletion of the soil seedbank.