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With head lettuce harvest a few weeks away, it would be wise to keep a look out
for corn earworm (CEW). These sneaky worms have caused problems for PCAs and growers
on the early fall head lettuce crops in the past few years. Last spring, high CEW
abundance was been reported by PCAs on late head lettuce crops, particularly in
the Dome/Wellton areas. Although CEW pheromone trap catches this fall have been
much lighter than last fall or spring, one never knows what to expect in the field.
Nonetheless, CEW can be very damaging in early fall head lettuce crops where once
head formation begins larvae will usually bore into the head almost immediately
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 virtually 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 or cup over,
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 if heavy pressure is sustained
near harvest. Most contact insecticides recommended for Lep larvae are active against
CEW. In a lab bioassay conducted this past spring, CEW larval mortality was most
rapid when exposed to Lannate, 0.5 lb (>90% mortality in 1 hr after exposure) and
pyrethroids, high rates (>90% mortality in 3 hrs), followed by Radiant, 5 oz and
Coragen, 5 oz (>90% mortality in 6 hrs). By 24 hrs, mortality was 100% for all the
treatments. 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.
These are Sneaky Worms!
Remember, When in Doubt . . . . . “SCOUT”
Click picture to listen to John’s update
To contact John Palumbo go to: jpalumbo@ag.arizona.edu |
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For questions or comments on any of the topics please contact Marco Pena at the Yuma Agricultural Center.
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