Managing Diamondback Moths a Parasitoid of Diamondback moth larvae
Diamondback moth larvae
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he diamondback moth (DBM) became a severe problem for Valley growers in the fall of 1986 with control failures due to in secticide resistance occurring through most of the late 1980’s. During the 1990’s, DBM populations experienced a few control failures in the spring with levels reaching 38 larvae per plant while in the fall these levels only reached two larvae per plant. The implementation of a cabbage IPM program in the early 1990’s was successful at reducing the number of sprays as well as controlling the worm complex, including DBM, and producing an acceptable yield of high-quality cabbage. Populations of DBM remained at manageable levels throughout the following decades. However, last year was a tough one for controlling this pest. There was significant pressure and some reports of insecticides not providing adequate control. The diamondback moth is renowned for its ability to develop resistance to insecticides, sometimes within just a few years. Prophylactic or “calendar spraying” using conventional/synthetic insecticides has led to frequent, repeated exposure to many effective insecticides, resulting in decreased efficacy. In South Texas we can have multiple generations of this pest throughout the growing season, which favors the development of resistance. Insecticides select individual DMB that can tolerate exposure to a toxin and survive to pass this trait on to future generations. Generally, tolerance to one insecticide results
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in tolerance to all insecticides with the same mode of action (MOA), categorized by IRAC group numbers. Each MOA has a designated IRAC number and all insecticides with the same MOA will have the same IRAC number. To restore the efficacy of current insecticides and extend the usefulness of new, novel insecticides, it is incredibly important to use them judiciously, rotate between IRAC groups, and include non-chemical methods whenever practical. In other words, employ an integrated pest management plan. Biological/natural control for DBM already present in the Valley include two larval parasitoids. Diadegma insulare and Microplitis plutellae, which have been found to reach between 20 and
