Now that the weather is beginning to break in the desert and worm pressure has slowed down, PCAs can finally take a breath and look forward to the winter and spring seasons. However, it is important that you not forget about leafminers, particularly as the first produce fields approach harvest. Leafminer numbers have been light-moderate thus far this season, but we have recently observed high numbers (both adults, larvae and mines) showing up on melons and lettuce here at the Yuma Ag Center. 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, these traps have been located near or adjacent to fall melons, cotton or alfalfa. With temperatures forecasted to be in the 70-80s 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 they are currently present. They 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 the tender growing leaves. The good news is that they can be effectively controlled with currently available products. 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 they cause significant damage. Similarly, Agri-Mek at 8-12 oz can provide long residual control. Be sure to include a penetrating adjuvant with these products to enhance larval control. For more information on leafminer biology and management please go to Insect Management: Leafminers.

Leafminer Adults and Damage to Lettuce

To contact John Palumbo go to: jpalumbo@ag.arizona.edu

For questions or comments on any of the topics please contact Marco Pena at the Yuma Agricultural Center.
College of Agriculture, The University of Arizona, Tucson, AZ.