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Published July 13, 2010, 07:53 AM

Grasshopper threat dims, for now

The region’s cool, wet weather has helped to hold down a predicted grasshopper outbreak.

By: Jonathan Knutson, Agweek

The region’s cool, wet weather has helped to hold down a predicted grasshopper outbreak.

But it’s too soon to declare victory over the insects, especially since they’re causing big problems in some areas.

“They really haven’t been a problem (in North Dakota). But we could see more of them if the weather turns warmer in July,” says Janet Knodel, North Dakota State University Extension Service entomologist in Fargo.

Producers should continue to scout ditches and field edges for nymphs, which are young grasshoppers without wings, experts say.

Though most of the region so far has escaped a major outbreak, several counties in west-central South Dakota are being hit hard.

“We’ve got a mess. It’s not pretty,” says Maurice Lemke, extension agent in South Dakota’s Ziebach County.

Grasshopper numbers have been building for several years in Ziebach and surrounding counties.

“They’ve just really taken off this year,” he says.

Surveys have found more than 50 grasshoppers per square yard at some locations in the county.

To put that in perspective, the federal government says grasshopper suppression treatment is warranted when grasshopper density exceeds 15 per square yard.

The alfalfa harvest in Ziebach County already has suffered, and grasshoppers are beginning to damage corn and other field crops, too, Lemke says.

Damage on some rangeland might prevent cattle from grazing on it this winter, possibly forcing ranchers to sell some cattle, he says.

The pesticide Dimilin is being sprayed to fight the insects, he says.

The South Dakota Department of Agriculture in mid-June issued an emergency exemption allowing the use of Dimilin to control grasshoppers in alfalfa hay and alfalfa mix fields west of the Missouri River.

USDA predicted problems

Late last year, USDA’s Animal and Plant Health Inspection Service forecast heavy outbreaks of grasshoppers across much of the western U.S. — potentially the worst in the past two or three decades.

A grasshopper can eat about half about its body weight in vegetation each day, so crops and pastures can be damaged badly during an outbreak.

One measure of how livestock producers can be hurt: Thirty pounds of grasshoppers eat roughly as much plant material as one 600-pound steer.

Recognizing the threat, the federal government set aside an extra $11 million this year to combat grasshoppers on rangeland.

The heaviest outbreaks were projected for Montana, North Dakota, South Dakota, Wyoming and Nebraska, with lesser outbreaks predicted for Idaho, Nevada and Utah.

The prediction was based on the unusually high number of adult grasshoppers found in 2009 in those states, which indicated that a large number of eggs had been laid.

September 2009 was unusually warm, leading to more grasshopper eggs in the ground.

APHIS estimated that 47.8 million acres in the western United States, primarily Nebraska and Montana, could be hit with 15 or more grasshoppers per square yard this summer.

In the Northern Plains, grasshopper eggs usually begin to hatch in late April to early May, with the peak hatch in the middle of June.

This year, however, frequent rains have killed many of the young grasshoppers. All the moisture also has led to disease that killed many of them, Knodel says.

Averted? Or just delayed?

Frequent rains in Montana appear to have held down grasshoppers in the state, says Kevin Wanner, entomologist with the Montana State University Extension Service in Bozeman.

He says he’s heard few complaints about grasshoppers so far this summer from farmers and ranchers.

Vegetation is relatively lush in much of the state, so grasshoppers could be doing damage without attracting much attention, he says.

Farmers with lentils should be particularly careful because grasshoppers can do major damage to flowering lentils, he says.

Drawing conclusions about weather and its affect on grasshoppers is tricky, he says.

It’s possible that wet, cool conditions have simply delayed grasshopper problems, rather than defuse them, particularly if the weather turns hot and dry, Wanner says.

“It’s still wait and see,” he says.

Female grasshoppers get bigger and produce more eggs in hot, dry weather, he says.

Typically, grasshopper outbreaks occur in two- to four-year cycles. This is the second year in the current cycle, and it’s much too early to predict if the cycle is over, Wanner says.

Reaction from APHIS

APHIS continues to survey grasshopper conditions in 17 western states, including Montana, South Dakota and North Dakota, says Charles Brown.

Brown, based in Maryland, is rangeland grasshopper and Mormon cricket suppression manager for APHIS.

The wet spring clearly has hampered grasshoppers, he says.

But there are hundreds of grasshopper species, and the weather has had more affect on some species than others, he says.

Ag producers with concerns about grasshoppers should check first with their county extension agent, APHIS says.

APHIS also offers its plant protection and quarantine program to help ag producers combat grasshoppers.

Information: www.aphis.usda.gov or grasshopper-program@aphis.usda.gov.

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