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

Thrips management in desert produce

By John Palumbo, UA Research Scientist and Extension Specialist

With the rain experienced over the Feb. 18 weekend, a decline in thrips numbers on leafy vegetables is likely to occur.

Precipitation amounts varied throughout the Yuma area with the highest recorded AZMET levels recorded in the Gila Valley at 0.46 inch, and the least recorded at the Roll station (0.14  inch). The Yuma Valley received at least 0.40 inch of rainfall on Feb. 19.

However, as experienced last year with much heavier and more frequent rainfall, these declines can be short-lived. Typically, heavy rainfall can dislodge or even drown adult thrips on plants and can suffocate the larvae in the soil if it remains wet for prolonged periods. Once the plants dry, adults can quickly move back onto plants.

Another factor that pest control advisers should be concerned with this time of the year is thrips "bioconcentration"which occurs each year in late February and March as lettuce acreage declines in the low desert due to the end of the season. This is coincident with an increase in thrips abundance that occurs due to higher temperatures.

Each time a lettuce field is harvested and disked adult thrips populations disperse from these areas into the next available lettuce field. As lettuce acres are reduced at the end of the season, this creates a bottleneck effect that concentrates high numbers of thrips adults on the remaining fields under production.

This can often make chemical control very difficult, particularly in March, as thrips may continually re-infest fields following spray applications.

Random notes: Radiant (6-8 ounce/acre) and Lannate (0.75 lb) + pyrethroid (high rate) are providing good residual efficacy of thrips in our trials at the Yuma Ag Center.

Remember, the key to good thrips control is to prevent immature populations from becoming established.

For more information on the identification, biology, ecology, and management of thrips on desert produce, read " Insect Management on Desert Produce Crops: Western Flower Thrips" and "Thrips Management in Desert Leafy Vegetables" .

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