Spider mite infestations in 2012 across the entire Texas High Plains were among the worst producers have had to deal with in a number of years, according to a Texas A&M AgriLife Extension Service entomologist.

Dr. Ed Bynum, AgriLife Extension entomologist in Amarillo, said corn producers primarily saw populations of the Banks grass mite, which “are supposedly easier to control than the two-spotted spider mite.”

But this year many producers had a hard time controlling any mites with a single miticideapplication. In many instances, mites were never controlled with multiple applications.

“As we look back on the season, several factors contributed to the rapid mite infestation development and poor control,” Bynum said.

One factor was the timing of the hot, dry conditions, which provided an ideal environment for mite populations to get out of hand. Daytime temperatures began to reach the high 90sand into the 100sduring the last half of June and again during mid-July into August.

Coupled with the dry conditions, mite populations established across the field in June, he said. Then in July, corn fields were tasseling and starting grain development growth stages, which further enhanced the reproductive capacity of mites.

“Once mite infestations moved up the plant and began causing damage below the ear leaf, the populations reached levels that even a miticide application controlling 60 percent to 80 percent of the mites left sufficient numbers to rebound rapidly,” Bynum said.

The entomologist said one observation this year was that mite populations developed earlier and faster on corn grown under drip irrigation.

Another factor in some fields, he said, was insecticides applied for other insects, such as southwestern corn borers, western bean cutworms and western corn rootworm adults, either eliminated natural predators and/or further stimulated the reproductive capacity of mites.

“Previous research has shown pyrethroid insecticides will flare mites. Even the use of bifenthrin will not control mites, except in a few locations,” Bynum said. “Applications of dimethoate for other insect pests are also ineffective at controlling mites due to their developed resistance to this insecticide, and dimethoate further eliminates the natural predators.”

Bynum said predators important to managing mite infestations include western flower thrips early in the season when migrating out of wheat, and six-spotted thrips, minute pirate bugs, predatory mites and spider mite destroyer beetles later in the season.

Another consideration is spray coverage, which is a key factor to the level of control with any miticide application.

“With the currently registered miticides, spray deposition into the canopy to where mite infestations are located is even more critical for effective control,” Bynum said. “Research has shown that Comite, Oberon, Onager and now Zeal are effective under most situations and conditions.”

This year, even when these products were mixed with crop oil but were sprayed during the heat of the day, many of the droplets may not have made it to the canopy, he said. Also, for these products to be maximally effective, they have to rely on help from natural predators.

“Fortunately, the products are very safe on predators that eat mites,” Bynum said. “The predators act in concert with the miticides to ‘clean up’ any escapees and usually extend control for the remainder of the season. When this balance is disrupted, mite infestations are free to blow up.”