The latest Arizona Vegetable Integrated Pest Management Update from the University of Arizona (UA) Cooperative Extension in Yuma, Ariz., released Nov. 1, 2011.

Leafminer management on fall lettuce

By John Palumbo, UA Research Scientist and Extension Specialist

Now that the hot weather is beginning to break in the desert and worm pressure has slowed, pest control advisers can finally take a breath and look forward to the winter and spring seasons.

It is important to not forget about leafminers, particularly as the first produce fields approach harvest. Leafminer numbers have been light to moderate so far this season, but we have recently observed high numbers (both adults, larvae and mines) on melons and lettuce at the University of Arizona (UA) Yuma Agricultural Center (YAC).

Furthermore, an increase in adult flies has been observed on yellow sticky traps used for monitoring whiteflies throughout the area over the past week or so. In most cases, the traps were located near or adjacent to fall melons, cotton, or alfalfa.

With temperatures forecast in the 70s to 80s for the next week, leafminer adult movement should subside, but larval activity could easily cause damage if left uncontrolled in lettuce or baby leaf fields where currently present.

This can cause significant damage to older, pre-harvest lettuce by feeding and damaging wrapper leaves of head lettuce and romaine. Pupae collecting within the leaf margins can also be considered contaminants.

In addition, baby leaf lettuces, spring mixes, and spinach are susceptible to larval feeding (mining) on tender growing leaves.

The good news is effective control is available with products on the market. Radiant (5-7 oz.), Coragen (5-7 oz.), and Voliam Xpress (9 oz.) applied at higher rates can effectively kill developing larvae in the leaves before causing significant damage. Similarly, Agri-Mek at 8-12 oz. can provide long residual control.

Include a penetrating adjuvant with these products to enhance larval control.

For more information on leafminer biology and management, click on this link: Insect Management: Leafminers.

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