Spider mites a new problem for beet growers

Published online: Jan 08, 2014

NAMPA, Idaho-Sugarbeet growers in Idaho have had to deal with significant numbers of two-spotted spider mites recently and no one's sure whether the insect will become an annual pest for that crop.

While the mites have been a problem for other Idaho crops such as corn, dry beans, hops and alfalfa for years, they only started showing up in large numbers in sugarbeet fields two years ago.

"No one was too concerned about this beast until 2012," said Erik Wenninger, an entomologist at University of Idaho's Kimberly research and extension center. "It has only recently become a problem in sugarbeets."

Two-spotted spider mites, which have two distinctive spots on their body, appear as pinhead-size spots on the underside of leaves.

Growers will typically see signs of the insects-webbing, discoloration and yellowing of foliage, dying leaf tissue-before they see the mites themselves.

The feeding damage the mites cause sugarbeet foliage interrupts the transport of water and nutrients to the plant.

Wenninger said the insects do well in the hot, dry conditions that Idaho growers faced during the 2012 and 2013 growing seasons. Before that, the area had a stretch of relatively cool, wet springs.

Two-spotted spider mites can have multiple life cycles during one season and the hotter the temperature, the more life cycles they have.

There is a possibility the insect has developed some resistance to insecticides and the growing number of corn acres in the region might also be a factor in their increase, Wenninger said.

The cause of similar outbreaks in sugarbeet fields in California is unknown, he added.

"We've seen high levels of spider mites the last couple of years," said New Plymouth, Idaho, farmer Galen Lee. "Whether that's a fluke or not, I don't know."

The spider mites are typically found in weedy areas, along ditch banks or areas of the field with heavy dust deposits. Sprinklers reduce dust deposits that accumulate on plant leaves.

"If you have surface-irrigated fields, they may be more likely to have spider mite issues than sprinkler-irrigated fields," Wenninger said.

Keeping weed populations down can also help producers control spider mites, he said.

A lot of beneficial insect predators can help control two-spotted spider mite populations and the predatory mite does the best job, Wenninger said. Farmers with spider mites should reduce insecticide spraying to when really necessary because of the impact the chemicals can have on beneficial insects, he added.

Wenninger encouraged growers to scout for signs of mites on the edge of fields or in adjacent fields.

"Those guys can move around quite a bit," he said. "A problem in one adjacent field one day can be a problem in your field tomorrow."

Source: www.capitalpress.com