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Published June 25, 2012, 09:38 AM

Hop to it

Their numbers aren’t dangerously high yet, but Gary Adams continues to worry about grasshoppers.

By: Jonathan Knutson, Agweek

Their numbers aren’t dangerously high yet, but Gary Adams continues to worry about grasshoppers.

“There may not be fewer of them (than feared). They may just be later,” says Adams, the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service’s state plant health director in Montana.

He and other experts across the Upper Midwest say it’s too early to predict how much damage grasshoppers might do this summer. Young grasshoppers frequently drown in heavy rains, so substantial precipitation in the next few weeks would reduce their numbers.

But a 2011 APHIS survey of adult grasshoppers found that the pests could be a threat this summer in much of the Upper Midwest, particularly Montana. Warm, dry conditions across the region last fall extended the grasshoppers egg-laying season, and the unusually mild winter also favored the insects.

Current grasshopper counts in Montana aren’t particularly troubling. But the extended egg-laying season means many grasshoppers will be born later than usual, which could push up their numbers substantially in coming weeks, Adams says

The survey says …

About 550 million acres in the United States could be at risk for grasshoppers this year, according to the APHIS survey.

Of that number, 35.6 million acres — most of them in east-central Montana and west-central Nebraska — face the threat of 15 or more adult hoppers per square yard. An area with that level of infestation, the equivalent of roughly 72,000 or more grasshoppers per acre, is dangerous, especially in years when vegetation is relatively scarce.

A grasshopper can eat about half its body weight in vegetation each day. Thirty pounds of grasshoppers can eat roughly as much grass as one 600-pound steer.

Parts of North Dakota and South Dakota potentially could be hit with up to eight adults per square yard, while a few areas of South Dakota could face eight to 15 adults per square yard.

Get out and scout

Though it’s too early to determine how big a problem grasshoppers will be, farmers and ranchers should be scouting their land for the insects, says Jonathan Nixon, entomology field specialist with South Dakota Extension’s Rapid City regional office.

He recommends that producers use sweep nabs to determine the number of nymphs (young grasshoppers) in potentially troublesome fields or field margins: take 40 sweeps (one sweep followed by a one-yard step), then count the number of nymphs collected and divide by 10.

A count of 25 to 35 nymphs in a field margin or 15 to 25 nymphs in a field is considered light.

A count of 50 to 75 in a field margin or 30 to 45 in a field is considered threatening.

A count of 100 to 150 in a field margin or 60 to 90 in a field is considered severe.

A count of more than 200 in a field margin or more than 120 in a field is considered extremely severe.

Keep in mind that the number of nymphs in early summer will be higher than the number of adult grasshoppers later in the summer. At least a few of the nymphs will be killed by weather and natural predators.

In general, field crops or margins should be treated when the nymph count reaches the threatening stage, according to information from SDSU Extension.

Sweep nets can be purchased online and at some farm stores, Nixon says.

Grasshoppers aren’t a problem yet in North Dakota, says Janet Knodel, North Dakota State University Extension entomologist.

But the insects have the potential to be a threat in some areas of North Dakota, particularly the western part of the state, and producers should be vigilant, she says.