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Vegetable IPM Updates Archive
Cooperative Extension
Corn Earworm in Spring Head lettuce (February 18, 2015)
As the produce season begins to wind down, it would be wise to keep a look out for corn earworm (CEW); they are historically active on spring head lettuce. In the last few years, unusually high CEW abundance has been reported by PCAs on late head lettuce, particularly in the Dome/Wellton areas. Given the CEW trap catches this fall and winter, one might expect to see more CEW than normal, but then again it is impossible to predict. Nonetheless, CEW can be very damaging in spring crops where once head formation begins larvae will usually bore into the head 1-2 days upon hatching. Corn earworm is much more likely to bore into lettuce heads than other Lepidoptera
larvae, rendering the heads unmarketable. Larvae may enter the head from any point on the plants, but can often be found burrowing in from the top half of the head. If fields are not watched closely, infestations may not be noticed until the head is harvested. Once inside the head, it is almost impossible to control the larvae with insecticides. Thus, pay careful attention for newly oviposited eggs (laid singly) on lettuce plants. If you are beginning to find eggs and suspect that CEW are active in the field when plants are beginning to head, it would be a good idea to treat. The UA nominal threshold for CEW in head lettuce from early heading to harvest is 1-2 larvae / 100 plants. Repeated insecticide treatments may be required to maintain low population levels near harvest. Most contact insecticides recommended for Lep larvae are active against CEW. Furthermore, the addition of a pyrethroid with thrips, aphid and/or fungicide sprays may be cheap insurance against larvae infesting heads as you approach harvest. For more information on CEW management and control recommendations see Insect Management on Desert Produce: Corn earworm / Tobacco budworm and the 2015 Lep Control Chart.

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