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Usually by late July field crops entomologists are getting pretty busy with corn rootworm (CRW) damage reports and getting the word out about their management. It’s not a usual year, however! Very low numbers of the first CRW adults were caught in our traps last week and the first roots that we dug out show little CRW damage. We called it: this is unlikely to be a good year for the CRW.
Back in late winter/early spring we talked about the effects of the extremely cold winter on egg survival. Predictions were cautiously optimistic as most entomologists in the region estimated significant mortality of the eggs owing to the deep freeze in much of the Midwest and Great Plains. Add to it abundant moisture and field flooding around hatch time earlier this summer that probably killed a lot of CRW larvae and the recipe for CRW population disaster is complete: many of them never made it to summer.
It’s too early to start a full-fledged celebration just yet. Scout cornfields for adults, both to monitor their potential impact on corn silks and to account for next year’s management decisions. Moreover, because a lot of corn went in the ground late this year owing to high precipitation during the planting season, pay special attention to the late-planted corn. It will be very attractive to CRW females as an egg-laying site since it will still be an excellent carbohydrate food source for them after most of the other corn will have finished pollination.
However, we may not see corn rootworm populations equally low along the I-29 corridor. Not all areas were under equally severe and prolonged cold spells last winter, or received flooding rains this spring and summer. Scouting and root ratings are important in determining if CRW management strategy needs to be modified. The most powerful CRW management strategy is rotation to a non-host crop such as soybean. The second best management option is rotation of Bt corn hybrids. The figures included in this article highlight elements of CRW biology that are relevant to their management and several options for growing continuous corn while managing CRW populations in a sustainable way. Visit iGrow.org and type in ‘corn rootworm’ in the search bar to find more resources.
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