Every effort has been made to provide correct, complete, and up-to-date pesticide recommendations. Nevertheless, changes in pesticide regulations occur constantly, and human errors are still possible. These recommendations are not a substitute for pesticide labeling. Please read the label before applying any pesticide.
Northern Corn Rootworm is green.
Western Corn Rootworm is yellow with distinct black stripes.
The female Western is slightly larger and more distinctly striped.
Eggs are laid in the previous season and begin attacking corn as larvae in June the following season.
Eggs are laid in corn fields, so corn must be following corn for a threat to exist.
Damage can result in physiological yield loss or harvest loss as a result of lodging.
Adults begin emerging in late July and feed on the silks.
Although rare, heavy silk feeding by the adults can interfere with pollination.
If some silk clipping does occur, as long as there is 1/2 in. of silk showing pollination may occur.
Late planted fields (relative to other area fields) are at a possible higher risk for damage.
Corn Rootworm Larva 1/2"
Western Corn Rootworm 5/16"
Northern Corn Rootworm 1/4"
All corn fields that will be planted to corn the following year should be scouted for egg-laying adults from late July until frost. Count beetles per plant and follow the sequential sampling plan shown below. Remember that each Northern counts as 0.5, while each Western counts as 1.0.
Sample weekly until you have three consecutive below-threshold samples, or you have above threshold numbers.
If you choose not to scout, remember that the following fields are considered high risk for damage next year:
Corn planted late this year, especially if it will be planted early next year.
Fields that seem to have high numbers, but no exact count was taken.
Fields with evidence of silk clipping and pollination interference.
N=Not at Threshold, T=Threshold reached, RT=Running Total for all Samples
Sample until a decision is reached (N or T).
Use of the sequential sampling plan will indicate the presence of an economic threshold.
Crop Rotation is the best way to control corn rootworm.
Chemical control is sometimes necessary when economic populations occur in a field that cannot be rotated out of corn. Consult the current Cornell recommendations for corn rootworm larval control.
Evaluate your harvest last season. Were there lodged fields?
Review your crop plan for the previous and coming year to ascertain potential problem fields.
Consider a plan to scout your fileds during egg-laying time to determine the need for rootworm management in 1996.
For more information contact your local Cornell Cooperative Extension agent.