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Insect Poses Unusual Threat
May 7, 2012
By Jonathan Knutson, Agweek Magazine

Aster leafhoppers are uncommon in North Dakota -- so uncommon that Janet Knodel, North Dakota State University Extension Service entomologist, is drawing on a 1932 paper for information on how to fight them.

The mild winter of 2011 to 2012 has made this an uncommon spring. The insects are popping up in spring and winter wheat fields in North Dakota and western Minnesota, and producers need to check their crops to see if the insects are present, Knodel says.

Early identification and treatment is crucial, she says.

"Real young plants are more susceptible than mature plants," she says.

The insects will threaten other crops, too, when they emerge from the soil, she says.

Aster leafhoppers attack more than 300 species of plants, including sunflowers, canola, flax, potatoes, wheat, barley and oats.

Normally, aster leafhoppers aren`t much of a threat on the Northern Plains; they pose more danger to crops in states to the south. But this past winter was so mild that more of the insects were able to overwinter successfully as eggs in North Dakota, Knodel says.

Also, an unusually large number of aster leafhoppers overwintered successfully in South Dakota because of the mild winter there. Typically, the insects overwinter much farther south. Many of the South Dakota aster leafhoppers are moving into North Dakota, she says.

South Dakota State University Extension reports that unusually large numbers of the insects are popping up in the eastern part of the state.

Area gardeners also should be watching for the insect, SDCS extension says.

An aster leafhopper is about one-eighth of an inch in length, wedge-shaped, green to yellow, with three pairs of spots on its face, Knodel says.

She describes the insect as "mobile. It`s always moving."

The insect gets its name because it leaps from one leaf to another when disturbed.

Disease symptoms

Aster leafhoppers feed on plant sap and inject aster yellows, a pathogen, into the plant with its saliva during feeding. One example of the damage from aster yellows: wheat infected by it at the seedling stage won`t produce kernels.

Disease symptoms are similar to barley yellow dwarf virus. First comes a yellowing appearance, followed by leaves turning reddish-purple with brown edges, Knodel says.

She`s optimistic that early identification and proper application of insecticide will stop the insect from doing serious damage.

But there`s no recommended threshold of when wheat should be treated for the insect, she says.

According to the 1932 paper, "insecticide treatment should be considered when disease symptoms are noticeable and leafhopper numbers are high (clouds when you walk in fields)."

"I just wish we had more research" Knodel says.
Copyright 2012 Agweek Magazine
Story image: Photo of an aster leafhopper. Courtesy of Whitney Cranshaw and Wikimedia Commons
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