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

Winter weather and insects in desert vegetables

By John Palumbo, UA Research Scientist and Extension Specialist

The National Oceanic and Atmospheric Administration’s (NOAA) Climate Prediction Center predicts for the second winter in a row that a moderate to strong La Niña will be the dominant climate factor influencing weather in Arizona and California this winter.

This suggests our local weather should be warmer and drier than average from December through February.

What impact will this have on insect pests normally found on leafy vegetables and melons this winter? It is not certain since predicting insect abundance is like predicting the weather.

The University of Arizona (UA) has collected data over the years which suggests that aphid pressure on lettuce is historically lighter during growing seasons when rainfall amounts are low (less than one-quarter inch). Similarly, seed corn maggot infestations are generally less severe under warm and dry growing conditions during the winter.

In contrast, western flower thrips abundance is historically higher under warm and dry weather conditions. From January through March 2010, we received over four inches of rain in the Yuma Valley. Thrips numbers were very low in UA research trials and seed corn maggots were quite damaging in a number of crops that spring.

If relying on the La Niña predictions, one might assume that aphid and seed corn maggot pressure will be lighter, and thrips numbers much heavier this winter and spring. Keep in mind - there are a number of other abiotic and biotic factors that also influence insect abundance.

To be on the safe side, "When in doubt, scout."

Contact Palumbo: (928) 782-3836 or