The latest Arizona Vegetable Integrated Pest Management Update from the University of Arizona (UA) Cooperative Extension in Yuma, Ariz., released Aug. 9, 2011.

IPM guidelines for beet armyworm in lettuce

By John Palumbo, UA Research Scientist and Extension Specialist

The beet armyworm, Spodoptera exigua, is a major pest of leafy vegetables grown in the Desert Southwest. Typically, beet armyworm populations infest newly planted fields soon after plants emerge in early September and can remain heavy through early November under favorable weather conditions.

Fortunately for local pest control advisers (PCAs), several insecticide alternatives are available that provide excellent residual activity on this pest. Many products have different modes of action (MOA) that can be alternated throughout the growing season. The rapid development of resistance by beet armyworm to insecticide compounds should not readily occur.

However, if an insecticide compound, or products with the same MOA, are used repeatedly for beet armyworm control in the same field, the risk of resistance increases significantly.

This is particularly important with the Diamide group of insecticides (IRAC group 28) because the products can be applied as foliar sprays and soil injections, and because there are currently six Diamide products labeled in leafy vegetables with the same MOA (Coragen, Durivo, Voliam Xpress, Voliam Flexi, Synapse and Vetica).

Applying these Diamide products to the soil at planting, and applying them as foliar sprays in the same field, can expose multiple generations of beet armyworm to the same MOA. That is not a good way to use these products to remain effective for more than a couple of years.

Since the Diamides, as well as the other products currently available (Radiant, Proclaim, Intrepid, Avaunt), are critical to effective management of beet armyworm and other Leps in leafy vegetables, PCAs should consciously avoid the overuse of these compounds.

The most effective way to delay the onset of resistance by beet armyworm in leafy vegetables is to consider the recommendations provided in the guidelines recently prepared entitled Insecticide Resistance Management Guidelines for Beet Armyworm in Lettuce.

Contact Palumbo: (928) 928-782-3836 or jpalumbo@ag.arizona.edu.