Caterpillars for the painted lady butterflies have caused crop damage for farmers this summer.

Drivers might be finding themselves paying for car washes after a few days to weeks of driving Washington County roads through kaleidoscopes of bright orange butterflies.

But if cleaning a car of bug splatter seems an extra burden, ask a soybean farmer what dealing with those butterflies and their caterpillar stage means to them.

Washington County farmers have seen crop damage due to higher than normal numbers of painted lady butterflies this season. More specifically, they've seen crop damage due to the butterfly's caterpillars, often called thistle caterpillars, feeding on their soybeans.

"It's pretty widespread in the Dodge and Washington County area," said Nathan Mueller, an Extension agronomist in Dodge and Washington counties. "This is actually the second generation of caterpillars. We already had the first generation earlier this year, and that hit harder more in the southeast."

Mueller said he recently met with a group of 15 farmers and growers from Dodge and Washington counties. Mueller said the group, and many others who've called him, have reported the butterflies and caterpillars in their soybean fields. Some have even met the recommended threshold for spraying, which is 30 percent defoliation in soybean pre-flowering stages or 20 percent defoliation in pod-forming stages.

Farmers are currently seeing the second generation of caterpillars, Mueller said.

"The second generation is already forming its chrysalis, it's cocoon," he said. "That's why we're seeing so many butterflies again ... It may be next we'll start seeing caterpillars again."


A few of the painted lady, or "thistle," caterpillars Extension agronomist Nathan Mueller has seen in the Dodge and Washington County areas.

It's the brown-black, yellow-striped caterpillars, which grow up to 1.5 inches, who are the culprits for crop damage. Extension Entomologist Robert Wright said the caterpillars feed on thistles, sunflowers and legumes, such as soybeans.

Nebraska has seen thistle caterpillars on soybeans in the past, Wright said, but this year is more problematic for the crop because of the higher than normal number of butterflies that arrived about a month earlier than normal. The butterflies overwinter in Mexico and migrate north in the spring and summer.

"When they have a wet winter, spring, as they did this year, there are a lot of host plants for the caterpillars to grow on," Wright said.

He said the crop growing season usually sees two generations of caterpillars and butterflies. Though Wright said recent rain and cold weather encouraged development of disease in caterpillars, the county and eastern Nebraska is likely to see a third generation.

Mueller said the third generation of caterpillars means farmers should continually monitor their fields for the bug.

"For growers that sprayed maybe a week, week and a half ago, it is possible they might have to spray again two weeks from now," he said. "It's pretty uncommon to have to spray a soybean field twice in one season."

Farmers shouldn't spray for butterflies, however, Mueller cautioned. It's not the butterflies that are the biggest threat to crops, he said, and they might fly away to another area before they lay larvae.

Referencing painted lady butterfly articles written by Wright on the cropwatch section of the UNL Extension website, Mueller said spraying for butterflies, or before defoliation thresholds have been reached, can hurt economic return because of unnecessarily using the product. In addition, spraying can reduce beneficial insects that help control other pests.

In dealing with the butterflies and caterpillars, Mueller said it's just one more problem for farmers after an already tough planting season due to rain and flooding.

"That's what I'm hearing," he said. "It's been a tough year and now one more thing."

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