Now that spring has officially arrived, one question I've been contemplating is how did the cold weather this past winter impact pest pressure on our 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 Ag Center, I would say that 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. These 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, and with the cooler temperatures and multiple freezes experienced this winter, both lettuce plant growth and aphid activity were likely negatively influenced. Thrips numbers are beginning to rapidly increase now, but during Jan and Feb, their numbers remained very low. Although we saw less rainfall this winter, the cooler temperatures clearly suppressed population growth. In addition, it appeared to be a little windier this winter, but average wind speeds varied within Yuma County. Wind can influence insect movement, several abiotic/biotic factors, and of course, the ability of PCAs to spray crops. Finally, the hard freezes we experienced this winter certainly impacted plant growth, quality and insect management. This was especially evident in the Gila Valley for instance where the AZMET weather station recorded 7 days when temperatures dropped below 32°F for an average of about 5 hours per freeze. This is significant when you consider that no freeze events were recorded all of last growing season. In contrast, Roll had 30 days of below 32°F temperatures, compared to 19 last year. Looking forward, what impact these freezes have had on key pests of spring melons (i.e., whiteflies, cabbage loopers) remains to be seen. For a detailed summary of the winter weather data described above, please go to Winter Weather Conditions Yuma. For a more detailed discussion on the impact of weather on insects refer to the article Weather and Insects.

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.