Corn rootworm egg hatch in Iowa typically occurs from late May to the middle of June, with a peak of hatching around June 6th. This year the peak hatching date is ahead of schedule. Development of the hatching is driven by the soil temperatures and measured by growing degree days. About 50% of egg hatching occurs between 684-767 growing degree days. As you can see in the below map most of Iowa has already reached that.
A severe corn rootworm larval infestation can destroy nodes 4-6; each node has approximately 10 nodal roots. Roots pruning can interfere with water and nutrient uptake and make the plant unstable. A recent meta-analysis showed a 15% yield loss for every node that is pruned. Regardless of crop rotation, Bt rootworm corn traits, or applied insecticides, every field should be scouted for corn rootworms and injury to the roots. Looking at the corn roots 10-14 day after peak egg hatch is suggested because this is when the feeding will be fresh. Assess corn rootworm feeding and adjust management strategies.
