Yields can plummet by 6-10 tons/acre when spider mites infest silage corn. To add insult to injury, these tiny creatures also harm quality, according to recent University of California (UC) Extension research.

Silage-corn yield was compared on field plots treated with miticides vs. untreated check plots in 2010 and 2012. Quality wasn’t an original objective of the study, said Carol Frate, Tulare County farm advisor. She spoke at the Forage Seminars at World Ag Expo in February.

“But uncontrolled spider mites reduce quality,” said Frate. The untreated control plots had higher fiber, lower total digestible nutrients (TDN), and in one trial lower protein and lower starch in the other.


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In one of her trials, she counted more than 1,000 spider mites on a leaf from an untreated control plot.

“If you see any spider mites at all when the corn is still small enough to get in by ground, spray by ground,” she said. “It’s more effective than aerial application because the mites are on the undersides of leaves.”

Frate also advised switching use of labeled miticides to prevent resistance, as they have different modes of action. Brown midrib hybrids are more susceptible and dry, dusty conditions attract mites, she added.

For more on the trials and to view her presentation, visit the UC Tulare County's Pest and Weed Information.