Spider mites impacting seed corn fields in St. Joseph and Kalamazoo counties

Bruce MacKellar<mackella@msu.edu> , and Jon Zirkle, Michigan State University Extension -

The extreme dry conditions have caused spider mites to invade Michigan seed corn fields. Farmers are encouraged to walk fields to check for infestations.

Michigan State University field crops entomologist Christina DiFonzo was the featured speaker at a field meeting hosted by MSU Extension and Dale and Sally Stuby at their Centreville, Mich., farm on Thursday, August 2, discussing spider mites in soybeans. Following that meeting, we walked several seed corn fields in northern St. Joseph and southern Kalamazoo counties and found significant infestations of spider mites in several areas.

Because of the extreme dry conditions, spider mites, which rarely infest corn at serious levels, have invaded seed corn fields from the dry edges extending into the interior portions of fields. Most pyrethroids and pyrethroid/fungicide application used in seed corn fields to other seed corn pests kill beneficial enemies of spider mites, and thus flare mite populations. Only insecticides containing bifenthrin or an OP, or several selective miticides, are recommended to control spider mites on corn. Growers should watch for the tell-tale yellowish stippling injury on the seed corn leaves, which occurs first in the lower canopy and moves upward. Heavier infestations usually show signs of webbing on the underside of leaves.

Stippling injury
Stippling injury on seed corn leaves (upper canopy of a seed corn
field in St. Joseph County on Thursday, August 2).

Because of the limited number of leaves available in female inbred plants following de-tasseling, preserving green tissue following pollination helps kernel fill and seed corn yield. We encourage growers to walk fields to assess if spider mites are an issue in their areas. As with all pesticide decisions in seed corn production, growers need to visit with their seed company pest managers before making a decision to spray for these pests. DiFonzo will be putting together a comprehensive resource for the spider mite challenges faced in many crops in Michigan.

Mites, eggs and webbing
Mites, eggs and webbing on the underside of a seed corn leaf
from a field in southern Kalamazoo County on August 2.

This article was published by Michigan State University Extension. For more information, visit https://extension.msu.edu. To have a digest of information delivered straight to your email inbox, visit https://extension.msu.edu/newsletters. To contact an expert in your area, visit https://extension.msu.edu/experts, or call 888-MSUE4MI (888-678-3464).

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