Corn Earworm – Vegetable Crops Hotline

Corn Earworm

After a season of relatively low corn earworm activity, pheromone trap catches have taken a dramatic turn upward, especially in the northern half of the state. Catches of 100-200 moths per night in the trap are not uncommon currently. Keep in mind that the threshold for treatment is 10 moths per night, so these catches would be 10-20X the threshold. At this point, growers with late sweet corn should be beginning treating when about 30-50% of the plants are showing silks. Sprays should be applied every 2-3 days until silks turn brown. It takes 3 days for eggs to hatch so a reasonable question would be, why spray every 2 days?  Really what it becomes at this point is a numbers game. Even the best insecticide applied at the highest rate with excellent coverage will not provide 100% control. When counts are near the threshold the number of escapes is relatively low and tolerable. When you multiply the number of hatching eggs by 10 or 20-fold, the number of escapes is likely increased by a similar amount and that becomes intolerable. Spraying a little more frequently will help to reduce the number of escapes. The best products we have seen in our trials, since the development of resistance to the pyrethroids, are Coragen®, Radiant®, and Belt®. If you use the high rate of these products, and you should, you cannot stick to a single product because of limitations on the total amount that can be used per acre per season. So that means you will need more than one of these products. Some growers have asked if tank mixing a pyrethroid is useful during this late surge of activity. While I wouldn’t recommend that during the early season, I think that may be beneficial now because the pyrethroids will provide control of earworms that do not exhibit resistance.

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