Nov 11, 2015
Aphids in Desert Vegetables 2015
With the changing weather patterns (wind actively blowing out of the north and west), PCAs can anticipate an increase in winged (alate) aphids showing up on desert produce crops. Based on my observations over the past two decades, this is an annual occurrence with our key aphid pests on produce. Aphids that typically infest leafy vegetables do not over-summer in the desert. Rather, winged adults migrate into our cropping system from mountainous regions of California via wind currents during November/December. Once the aphids reach our desert valleys, they typically move from crop to crop until they find a suitable host to feed and colonize on. But don’t panic just because you suddenly find a few winged aphids on the plant. It is not uncommon to find winged aphids on lettuce or broccoli that do not colonize on the crop. An example of these would be cabbage aphid which will colonize and infest cole crops but not lettuce, spinach or celery. Other examples would include aphids that colonize small grains (i.e., corn leaf aphid) or alfalfa (i.e., blue alfalfa aphid). Because these aphid species will not colonize produce crops, it is important to be able to distinguish them from the aphids that do colonize and require management to prevent problems at harvest (i.e., green peach aphid, foxglove aphid, lettuce aphid, cabbage aphid). Proper aphid ID can also influence your choice of insecticide, but more on that in a later update. As mentioned in the last update, PCAs have been finding small colonies of cowpea aphids showing up on frame leaves in lettuce. That is a common occurrence every fall. Not to worry, experience has shown us that although small cowpea aphid colonies may be found on lettuce, the populations generally stay low on the plant on the frame leaves and rarely increase to levels causing contamination issues. But you never know. So keep an eye for these guys, as our El Nino weather this year may be more conducive to their development than normal. Local research has shown that aphids tend to be more abundant at harvest in lettuce in years with higher winter rainfall than average (see
Impact of Lettuce Planting Date on Aphid Contamination). Also, don’t forget that proper aphid identification is important; it can save a PCA time and money, and prevent unnecessary insecticide applications. If you find an unusual aphid in your produce, don’t hesitate to drop it by the Ag Center and we’ll get it identified for you. But if you want to be fast and accurate you might use the attached publication
Aphid Identification in Desert Produce Crops that may assist you in identifying winged and wingless (apterous) aphids important in leafy vegetables and cole crops.
To contact John Palumbo go to:
jpalumbo@ag.Arizona.edu
To contact John Palumbo go to: jpalumbo@ag.Arizona.edu
