Several environmental factors can have a significant influence on population development of western flower thrips in lettuce. For instance, the mild temperatures we have been experiencing the past month have been shown to promote thrips build up in winter lettuce. Rainfall can also impact thrips population growth. In dry years, thrips can increase rapidly and cause significant damage to lettuce if not properly controlled. In contrast, heavy rainfall can have a negative impact on thrips populations by submerging larvae in wet soil and washing adults from plants. Prior to the heavy rainfall we received last week ( 3.12 inches at the Yuma Ag Center ), populations of western flower thrips were quickly reaching damaging levels in untreated romaine and head lettuce plots. Samples taken several days following the storms showed that populations of thrips adult and larvae on untreated romaine plants were reduced by greater than 60% Figure 1 (PDF, 104KB). However, experience has shown us that thrips populations can quickly rebound to high levels if dry and warm weather conditions prevail.
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.