Several reduced-risk insecticides were evaluated for management of three lepidopteran cole crop pests, Plutella xylostella (L.), Pieris rapae (L.), and Trichoplusia ni (Hübner) in central Alabama in 2004 (spring and fall plantings) and 2005 (spring only). The following formulated sprays were evaluated: Dipel® (Bacillus thuringiensis subspecies kursatki), XenTari® (B. thuringiensis subspecies aizawai), Dipel XenTari (a premixed test formulation consisting of both subspecies of B. thuringiensis), Entrust® (a formulation of spinosad for use in organic crop production), and Novaluron (insect growth regulator). Variations in the populations of the three pest species were recorded from season to season with pest pressure being generally higher in both spring seasons than in the fall season. While moderate to high populations of P. xylostella and P. rapae were recorded in all three seasons, T. ni was detected only in spring 2005. An action threshold of 0.5 cabbage looper equivalents (CLE) per plant was used to determine the need for insecticide applications. Insecticide efficacy was determined by comparing densities of larvae and immatures (larvae pupae) of each pest species, crop damage ratings, densities of key non-target arthropods, and number of insecticide applications in plots treated with each material versus untreated control plots. All five reduced-risk insecticide formulations were effective in reducing infestations of the three lepidopteran pests and in providing marketable cabbage and collards in Alabama. Among the treatments, Entrust® consistently produced the lowest mean damage ratings with the minimum number of applications per season. No significant effects of insecticide treatments were recorded in the numbers of spiders and lady beetles found per plant. The results also suggest that the 0.5 CLE action threshold can be used to produce marketable cabbage and collards in Alabama with only minimal applications of reduced-risk insecticides.
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