Managing lepidopteran pests in cabbage with herbicide‐induced resistance, in combination with a pyrethroid insecticide

Abstract

AbstractS‐ethyldipropylthiocarbamate (EPTC) applied as a soil treatment or over‐the‐top spray on cabbage plants (Brassica oleracea L.) caused the leaves to turn ‘glossy’ for as long as 30 days. EPTC‐induced glossy plants were damaged significantly less than untreated plants by diamondback moth, Plutella xylostella (L.), imported cabbage worm, Pieris rapae (L.), and cabbage looper, Trichoplusia ni (Hbn.). Reductions in damage were equivalent to those obtained from treatment with permethrin. When used in combination with permethrin, EPTC provided additive control of damage by these pests. Our calculations show EPTC‐induced resistance to be cost‐effective. This use of EPTC has several limitations, however. Younger plants (<9 leaves) were killed or injured by the herbicide. The growth of older plants was not affected, but plants did not become glossy for ca. 10 days after they were treated with EPTC. The crop must be protected with insecticides until the plants are mature enough to treat with EPTC, and until treated plants become glossy. In addition, since the glossy trait is only effective against first instar larvae, populations of later instars on glossy plants must be reduced with an application of insecticide. Finally, EPTC formulations are water‐soluble and can be washed away from the plants by heavy rains and irrigation, which may make this use of EPTC impractical in some situations. Where its use is practical, and the indicated precautions are taken, EPTC‐induced resistance could reduce dependence on chemical insecticides and reduce selection for insecticide resistance in diamondback moth.