Spider Mites in Corn and Sorghum

General spider mite pressure

Spider mite pressure overall has seemed to declined, probably a result of recent showers. Spider mites are very small, 1/32 inch or less, and are difficult to see without magnification unless colonies are well developed. Eggs are very small pearly white spheres. Mites will migrate into corn from wheat or native grasses with the aid of wind. They will lay eggs on the underside of corn leaves which will hatch in 3-4 days. Larvae/nymphs will mature and begin laying eggs in 5-10 days. There may be 7 to 10 overlapping generations per growing season. Hot dry conditions favor rapid development of mite populations particularly after tassel.

Banks grass mites typically infest lower leaves first then move up the plant while two spotted mites may infest any leaf at any time. Banks grass mite and two spotted mite infestations of similar densities will result in similar damage. 

In fields with established mite colonies and a history of spider mite infestations a preventive miticide application should be considered. There are several foliar miticides which can be applied early season to reduce risks associated with spider mites. Remember current miticides are not systemic and will only protect the leaves which are sprayed and any subsequent growth will not be protected. Some of these pesticides are soft on beneficial organisms and may allow natural enemy populations to become established which will result in a more stable production system.