Evaluation of potential relay strip crops for predator enhancement in Texas cotton

A two-year study was conducted at the Texas Agricultural Experiment Station farm at Munday, Texas to evaluate different relay strip crops for predator enhancement in cotton. The study evaluated eight relay strip crop treatmen ts, including three fall crops (fall planted canola, Brassica rapa L., hair y vetch, Vicia villosa Roth, and wheat, Triticum aestivum L.), three spring crops (spring planted canola, forage sorghum, Sorghum bicolor L., and grai n sorghum, Sorghum bicolor L.), a relay crop system comprised of canola pla nted in the fall and grain sorghum in the spring, and cotton planted adjace nt to cotton as control. Each treatment consisted of four rows of the relay crop planted on both sides of an 8-row x 23-m cotton plot, replicated thre e times. Predator abundance was monitored weekly in strip crops and cotton throughout the crop season by taking a 15 s D-vac sample from each plot. Go tten aphids, Aphis gossypii Glover, and bollworm-budworms, Helicoverpa tea (Boddie) and Heliothis virescens (F.) combined, were monitored in cotton pl ots only. Aphid abundance was estimated during the peak aphid period by cou nting the number of aphids on 10 upper and 10 lower leaves of cotton plants within each plot. Bollworm-budworm abundance was estimated by counting the number of larvae per 4 row-m of cotton in each plot. Predator species comp osition varied significantly among strip crops, but it did not significantl y vary among cotton plots. Overall, strip crops significantly enhanced pred ator numbers in adjacent cotton plots during the first half of the growing season, but this effect dissipated after mid-July. Average aphid abundance in cotton was significantly affected by the adjacent strip crop, with the h ighest average number of aphids per leaf in control plots compared with num bers in plots adjacent to strip crops. A significant effect of strip crops on bollworm-budworm abundance was not detected, but the average bollworm-bu dworm larval abundance in our experimental plots remained below the economi c threshold, whereas the rest of the 83 ha of cotton in the same experiment al farm which employed the standard cropping system suffered from a severe bollworm-budworm infestation in both years. Average lint yields did not sig nificantly vary among strip crop treatments, but average yields in the stri p crop study plots were similar (1996) or significantly higher (1997) than in the plots where strip crop strategy was not employed. All the cover crop s evaluated in this study enhanced the predator numbers and suppressed the aphid abundance in cotton in both years. However, wheat and spring canola w ere the two candidate cover crops that significantly suppressed aphid numbe rs in cotton both years, indicating a higher relay strip crop potential tha n the other cover crops evaluated. Although strip cropping of wheat or spri ng canola significantly suppressed aphid populations in cotton, a relay sys tem consisting of canola planted in the spring adjacent to wheat planted in the fall might be more efficient than using a single strip crop in a pesti cide-free cotton production system.