Soybean Insect Pests Brought About By Drought

Soybean Insect Pests Brought About By Drought

Dry weather conditions and insect infestations have played a significant role in Iowa soybean production this year.

Weather conditions have played a large role in soybean production in 2012. With an unusually warm winter followed by an unprecedented drought, farmers across the Midwest faced a multitude of challenges this growing season.

In Iowa, spider mites emerged as the most prominent pest, and the drought was largely to blame for this potentially crop-crippling pest, notes Erin Hodgson, Iowa State University Extension entomologist. "This year we've seen an increase in spider mite populations compared to most years and usually drought, stress and high temperatures are perfect for spider mites to thrive," she says.

Drought and insects have pestered Iowa's soybean crop this year, lowering yield prospects statewide. Japanese beetle (pictured) and spider mites have shown up in many Iowa fields.

The drought conditions aren't the only factor that contributed to this year's insect and mite conundrum. While the hot, dry weather brought spider mites to many Iowa soybean fields, the unusually warm weather this past winter is to blame for other insect pests that invaded soybeans this season.

Japanese beetles also showing up--why the increase in Japanese beetles?
"We had more Japanese beetles this year, and I think that's because we had an exceptionally warm winter," says Hodgson. "The overwintering grubs had a higher likelihood of surviving and a kind of nice and easy warm-up in the spring. It was just ideal for them to complete their development into the adult stage."

Bean leaf beetle populations also increased this year due to the unusually warm winter weather. "Frost can kill insects, and an example would be bean leaf beetle, which is very susceptible to cold temperatures. They overwinter as adults in cracks and crevices, and we had a slightly higher number this year compared to the last couple of years," says Hodgson. "I think that's because the adults are able to survive more easily compared to most years where we've had a lot of frost."


In addition to increased insect pressure thanks to unfavorable weather conditions, extreme drought will contribute to lower soybean yields. However, Hodsgon has a positive outlook. "All things considered, I think our soybean crop in 2012 in Iowa looks pretty good. Soybeans generally compensate fairly well to drought stress. The soybean plant has the ability to abort pods or not fill as many seeds per pod if it is under stress, and still look relatively healthy above ground."

Yields will vary considerably this year, you won't know for sure until harvest
"I would expect yields to be lower than normal just because the soybean plants aren't getting enough water to fill grain as they normally could under normal rainfall and soil moisture conditions," Hodgson says.

While the drought itself can significantly impact soybeans, spider mites may prove to be most devastating. According to Troy Griess, Syngenta agronomic service representative in northwest Iowa, this pest can wipe out bean yields if soybeans are left untreated.

"If growers have a significant infestation of spider mites and don't do anything to control them when it's hot and dry, that could impact yields very dramatically," Griess says. "If growers let spider mites go unchecked and they actually spread throughout the plant, they'll basically shut the plant down. You already have a plant that's under stress from lack of water and too much heat. This spider mite pressure is just one more thing soybean plants are trying to compete with and that's going to make it really difficult for the soybean plant to yield."

Spider mites also having an impact on soybean yields in many fields in 2012
Soybean yields in some fields have been hurt by spider mites—especially those fields that had significant infestations but weren't sprayed with an insecticide. How much of an impact will spider mites have on yield? Griess says if the infestation is bad enough, growers can lose up to 100% if it kills the plants.

Griess provides updates on insects through a pest alert system offered by Syngenta. The Pest Patrol program allows growers to access weekly updates made by local agronomists on existing and prospective pest problems in their areas. Growers can opt in via text message, or visit the Pest Patrol website to receive information.

This system can alert growers about what pests are active, thresholds for treatment, and how current crop, weather and pest pressure conditions may affect that application.

While weather and pest conditions have been unusually strenuous this year, Griess says growers and retailers can avoid crop devastation by using his reports for Pest Patrol. "For most people, it's really easy to get a text. They just click on the link or call the number. They don't have to be at the computer."

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