Feb 9, 2022Don’t Forget Corn Earworm in Spring Head Lettuce
With local temperatures expected to increase in the next few weeks, insect activity should also start to pick up. Even though worm pressure has been light in the field for the past month or so, it would be wise to keep a look out for corn earworm (CEW). In the past, unusually high CEW abundance has occurred on late head lettuce, particularly in the Dome/Wellton areas. Our latest trap catches indicate that moth counts have been nearly bottomed out for some time. However, we did see a slight increase in CEW trap captures in the Dome and Yuma Valleys last week (~ 0.5 moths/trap/night). This is typical for February (Areawide Trap Network) and could be the calm before the storm. In the spring seasons where larvae were heavy (2014-2016), trap catches started to increase in late February-early March and peaked by mid-to-late March. These increased trap numbers should be used as an early indicator that moths are actively flying at night at higher abundance and PCAs should start to scout more aggressively for eggs and larvae. CEW can be very damaging in spring crops 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. If fields are not watched closely, infestations may not be noticed until the head is harvested. Once inside the head, control of larvae with currently available insecticides is not possible. 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 at regular spray intervals (~ 7days). The UA nominal threshold for CEW in head lettuce from early heading to harvest is 1-2 larvae / 100 plants. Essentially, you find one you spray. 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 Corn Earworm Management on Desert Produce and the 2022 Lep Control Chart.
To contact John Palumbo go to: jpalumbo@ag.Arizona.edu