Performance and economics of cotton weed management systems for the Texas Southern High Plains

In the United States, approximately 30 plant species that infest cotton fields are economically important weeds. Nearly three-fourths of the losses m cotton can be attributed to 10 types of weed species: momingglory species (Ipomoea spp.), common cocklebur (Xanthium strumarium), pigweed species (Amaranthus spp.), Johnsongrass (Sorghum halepense), nutsedge species (Cyperus spp.), bermudagrass (Cynodon dactylon), prickly sida (Sida spinosa), silverleaf nightshade (Solanum elaeagnifolium), croton species (Croton spp.), and sicklepod (Cassia obtusifolia). AU of these weeds except prickly sida, croton species, and sicklepod are found in the southwest United States (Frans and Chandler 1989). Without herbicides, United States cotton producers could face a 32% yield reduction due to weed competition (Abemathy 1981). Current preplant and preemergence herbicides control many small-seeded broadleaf weeds and annual grasses, but weeds not effectively controUed by current herbicides are an increasing problem. The development of transgenic cotton varieties and the registration of a new postemergencetopical (FT) herbicide offer improved potential for effective and economical control of many troublesome weeds on the Texas Southern High Plains.

Weed management systems utUizing glyphosate(Roundup Ultra) along with existing herbicides provide options to control weeds in conventional and reduced tillage, make applications during a wide window of cotton development, economically control a broad spectmm of weeds, and control weeds m an environmentally sound manner (Vidrine et al. 1996). Glyphosate is a non-selective herbicide that wiU control both annual and perennial grass and broadleaf weeds. Roundup Ready cotton varieties, which are resistant to glyphosate, were first available for wide-spread commercial planting in 1997. These new transgenic varieties aUow fanners to apply glyphosate PT through the 4-leaf stage and postemergence-duected (PD) until 20% open bolls.