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As summer progress, the pest profile in your corn crop can change, be aware for scouting purposes.

July 13, 2016

2 Min Read

Field studies at Colorado State University show that spider mites can be serious corn pests in the state, especially during hot and dry years, causing significant dry matter and grain loss, according to Assefa Gebre-Amlak, extension specialist, CSU.

In a pest notice released recently, Gebre-Amlak explains that there are two species of spider mites that attack Colorado - Banks grass mite, or BGM and two spotted spider mite, TSM. "Most corn growing areas are affected by BGM alone but north central Colorado, especially Weld and Larimer counties and production areas along the South Platte River are prone to serious mixed-infestations," Gebre-Amlak explains. "Spider mites feed on the undersides of leaves, eventually killing the leaf and leaving it with a scorched or burned appearance."

The Banks grass mite is found in corn from mid-whorl through the grain filling growth stages, while the two-spotted mite is usually not found on corn until after flowering. Key factors that can boost mite populations of the BGM include drought stress on the crop, elevated temperatures, low rainfall and low humidity.

Gebre-Amlak explains that most BGM problems occur in the drier corn growing areas and always associated with grasses. "For example, many problems in corn start when adjacent wheat fields dry down," he says. The two-spotted mite occurs in more humid growing areas, such as river bottoms.

The first signs of an infestation would be webbing on leaves and discoloration of plants. Initially, the BGM is most abundant on the lower third of the plant and density declines as the infestation moves up in the plant. Mites damage corn and small grains by piercing plant cells with mouthparts and sucking the plant juices.

"Proper irrigation to avoid drought stress is the key cultural practice for avoiding mite outbreaks, but once mite infestations are established, irrigation cannot reduce mite densities in corn," Gebre-Amlak says.

Use of an insecticide is justified when there is visible damage in the lower third of the plant and small colonies are present in the middle third of the bland before the hard dough stage. Check out the High Plains IPM guide for effect product for both species of spider mites management, and details economic threshold information. Learn more at the IPM site.

Source: Colorado State University

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