EFFICACY AND PERSISTENCE OF BEAUVERIA-BASSIANA AND OTHER FUNGI FOR CONTROL OF DIAMONDBACK MOTH (LEPIDOPTERA, PLUTELLIDAE) ON CABBAGE SEEDLINGS

The diamondback moth, Plutella xylostella (L.), is a key pest of cruci fers worldwide. Resistance by diamondback moths to chemical insecticid es and Bacillus thuringiensis Berliner toxins highlights the need for alternative controls. Crucifer growers often depend on seedlings produ ced in screenhouses and later transplanted to the field. Commercial se edlings can be contaminated with pesticide-resistant P. xylostella, le ading to control problems in the field. We evaluated the efficacy of B eauveria bassiana (Balsamo) Vuillemin applied as conidia in Mycotrol(R ) WP in three experiments by evaluating insect control, damage reducti on, and fungus persistence on treated leaves of cabbage seedlings. In one experiment, we also evaluated Metarhizium anisopliae Metschnikoff (Sorokin) applied as conidia in Bio-blast(R) and Paecilomyces fumosoro seus (Wize) Brown & Smith applied as freshly-cultivated unformulated b lastospores. We observed significant reductions, compared to controls, in insect populations and damage ratings when Mycotrol was applied on ce-or twice-weekly. Mycotrol treatments were as effective as a B. thur ingiensis product in preventing damage when three spray nozzles were u sed to insure adequate pesticide coverage. Mycotrol persisted on treat ed leaves in screenhouses for more than 2 wks, and mycosis of larvae r eared on these leaves was >50% 7 d after a single application of fungu s. Treatment with either M. anisopliae or P. fumosoroseus resulted in no significant reduction in insect numbers or damage, but each fungus persisted on leaves and caused mycosis in lab-reared larvae more than 2 wks after treatment. Mycotrol can provide an option for control of P . xylostella larvae on seedlings, and may be especially useful in a re sistance management program.