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Keep on the lookout for colonizing aphids (January 7, 2015)
Prior to the cold snap that occurred in the low desert last week, green peach aphid populations were steadily colonizing untreated lettuce plots here at the Ag Center. Very few winged forms were found, but small colonies of 5-6 nymphs could be found on about 10% of the plants. However, temperatures in the Yuma Valley dropped below 32° F several nights during that period. Past experience has shown that aphid populations tend to significantly slow down under these “cold” desert temperatures. That is essentially what we observed this weekend; population growth had stalled out and aphid numbers were the same as they were 2 weeks prior. However, past experience has also shown us that aphid population growth begins to increase again once the weather warms up. Our local
forecast suggests that temperatures will be in the mid-70’s for the next 10 days. Assuming the weather service is correct, these conditions may be ideal for aphid population growth. Thus far, in the Yuma Valley we have been finding mainly green peach aphid nymph colonies, and we have been picking up winged aphids on our yellow sticky traps. However, we have found winged Foxglove aphids in our celery. As temperatures increase foxglove may become more abundant (they tend to be more biologically active under warmer temperatures; that is when avg. temps > 60 F). If the field has been treated with imidacloprid at planting, then chances are you are in pretty good shape. But, continue to monitor as imidacloprid doesn’t generally last all season, and the neonicotinoids are marginally effective against foxglove and lettuce aphids. Regardless of whether you find green peach aphid or foxglove aphid the key to effective aphid management with foliar insecticide is to initiate sprays at the time apterous (wingless) aphids begin to colonize. Of course, this requires diligent scouting and sampling. On older lettuce, make sure you thoroughly examine developing heads/hearts. Fortunately, PCAs have alternatives for foliar aphid control. For more information on insecticide alternatives and Aphid Identification please visit Aphid Management in Desert Produce Crops – 2015 and Aphid Identification in Desert Produce Crops So keep your eyes open for new aphid colonies and plan accordingly. As Thomas Edison once said “Good fortune is what happens when opportunity meets with planning”.
Remember, When in Doubt . . . . . “SCOUT”

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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.

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