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

Management tips for 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 a moderate to strong La Niña will be the dominant climate factor influencing weather in Arizona and California this winter. This suggests that local weather in the Yuma County area should be warmer and drier than average from December through February.

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

However, like NOAA, we have 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 .25 inches). Similarly, seed corn maggot infestations are generally less severe under warm and dry growing conditions during the winter.

In contrast, western flower thrips abundance has historically been higher under warm and dry weather conditions. Last winter (January - March) we received over four inches of rain in the Yuma Valley and thrips numbers were very low in our research trials. Seed corn maggots were damaging in a number of crops last spring. 

If one chooses to rely on the La Niña predictions, one might predict 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. Historical trends in insect abundance on desert crops and guidelines for management were presented at the 21st annual Fall Desert Crops Workshop in Imperial, Calif. last week.

A copy of that presentation can be found at this link.

Contact Palumbo: (928) 782-3836 or