Western flower thrips are now beginning to increase throughout the area. They have slowly been increasing in the Yuma Valley, but reports from the Dome Valley area suggest they are occurring in much higher numbers there. With the light rain we experienced last week, we wouldn't anticipate any significant reduction in numbers like we usually see in wet springs. Typically, heavy rainfall will dislodge or even drown adult thrips on plants, and can suffocate larvae in the soil if it remains wet for prolonged periods. Historically in dry, warm winters like we're experiencing this season, thrips numbers have been found in much higher at this point in time. That has not been the situation to date and we're not quite sure why. However, another factor PCAs 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. Each time a lettuce field is harvested and disked, adult thrips populations disperse from these areas into the next available lettuce field. This is generally coincident with higher temperatures that are suitable for thrips development. As the number of lettuce acres become reduced near 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 adults may continually re-infest fields following spray applications. Research Note: Under current population pressures, Radiant (7 oz/ac) and Lannate (0.75 lb) + pyrethroid (high rate) are providing good residual efficacy of thrips in our trials at the Yuma Ag Center. The key to preventing thrips from significant scarring leafy vegetable plants is to prevent immature populations from becoming established. For more information on the identification, biology, ecology and management of thrips on desert produce please visit these links: Thrips Management in Desert Leafy Vegetables - 2012 and Insect Management: Western Flower Thrips

Remember: When in Doubt-Scout.

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.