Oct 28, 2020Time for Seasonal Aphid Movement into the Desert
Now that worm pressure has slow down a bit, you’re probably thinking about what’s next. With the seasonal transition to cooler temperatures beginning to occur, along with shorter days and consistent N-NW winds, you will likely begin to see an increase in winged aphids showing up on desert produce crops. Winged aphid numbers on yellow sticky traps were noticeably higher in the Bard, North Gila and Yuma Valleys over the past week. This is not a surprise; experience tells us that this is an annual occurrence. The key aphid pests found on winter produce (i.e., green peach aphid, foxglove aphids, cabbage/turnip aphids) do not over-summer here, rather they migrate into our cropping system from mountainous regions of southern California via wind currents during the fall. They can also hitch a ride on transplants originating from the coast. We’ve already seen a little of that this fall. Once the aphids reach our desert valleys, they typically land on native vegetation and then into produce fields, moving among weeds and crops until they find a suitable host to feed and colonize on. They might show up earlier this year given how dry the surrounding desert is. No need to panic if you suddenly find a few winged aphids on a lettuce plant. But it is important that you correctly identify the aphid species present. This time of the year it’s not uncommon to find winged aphids on lettuce that do not colonize the crop. For example, in the past couple of weeks PCAs have been reporting winged cowpea aphids on their lettuce and Cole crops. Not surprising given the high numbers infesting alfalfa this fall. Once the weather really cools off, they should disappear. Other examples of winged aphids that can be found on produce crops would include aphids that colonize small grains (i.e., oat bird-cherry 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, turnip aphid). Proper aphid ID can also influence your choice of insecticide, but more on that in a later update. Don’t be surprised if you start finding small colonies of cowpea aphids or melon 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 a close watch out for these early aphids in your crops. Bottom Line: 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. If you want to make fast and accurate IDs, you might use the attached publication Aphid Identification in Desert Produce Crops that can assist you in identifying winged and wingless (apterous) aphids important in leafy vegetables and cole crops.
Name that pest
To contact John Palumbo go to: jpalumbo@ag.Arizona.edu