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

Winter weather: impact on produce pests this year

By John Palumbo, UA Research Scientist and Extension Specialist

Spring has officially arrived and one question I've been contemplating is how did the cold weather this past winter impact pest pressure on winter vegetables?

There is no doubt that temperatures throughout Yuma County were considerably cooler this winter relative to last year, particularly during January and February. Based on my observations at the Yuma Agricultural Center, I would say aphid and thrips numbers were lower than what we typically see during this period.

It is quite reasonable to assume that the lower winter temperatures, coupled with lower rainfall amounts, likely kept aphid numbers relatively low.

The cooler temperatures may also explain why, in some cases, Movento appeared to provide inconsistent activity against aphids. The systemic activity of the compound is influenced by the growth of the plant. With the cooler temperatures and multiple freezes experienced this winter, lettuce plant growth and aphid activity were likely negatively influenced.

Thrips numbers are beginning to rapidly increase now, but during January and February the numbers remained very low. Although we saw less rainfall this winter, the cooler temperatures clearly suppressed population growth.

In addition, it appeared to be windier this winter but average wind speeds varied within Yuma County. Wind can influence insect movement, several abiotic-biotic factors, and the ability of pest control advisers to spray crops.

Finally, the hard freezes experienced this winter certainly impacted plant growth, quality, and insect management.

This was especially evident in the Gila Valley where the AZMET weather station recorded seven days when temperatures dropped below 32 degrees F. for an average of about five hours per freeze. This is significant since no freeze events were recorded in the last growing season. In contrast, Roll had 30 days of below 32 degree F. temperatures, compared to 19 last year.

Looking forward, the impact these freezes will have on key pests of spring melons (i.e., whiteflies and cabbage loopers) remains to be seen.

For a detailed summary of the winter weather data described above, click on this link -  Winter Weather Conditions Yuma. For a discussion on the impact of weather on insects, click on this link - Weather and Insects.

Contact Palumbo: (928) 928-782-3836 or