Grasshopper population is still hopping

News
Jul 9, 2010

Imagine an area that is 3 feet by 3 feet square. Now, imagine a grasshopper in it. Imagine 14 grasshoppers in it. Imagine 50 grasshoppers in it. Imagine 100 grasshoppers in it. The square with 14 grasshoppers indicates there may be a need for control. The square with 50 grasshoppers is how some areas of Wyoming looked last year. The 100-grasshopper square is how many areas look this year.

"We’re seeing grasshopper numbers that are just through the roof in some areas," said Slade Franklin, weed and pest coordinator with Wyoming Department of Agriculture in Cheyenne. The grasshopper numbers predicted by the number of egg-laying adults last year have been pretty accurate, he says. "The late moisture and cool temperatures got some people’s hopes up that we wouldn’t have the outbreak that was predicted, but if anything, it delayed and prolonged it," he said.

Grasshoppers require soil temperatures of 50 degrees Fahrenheit or above to hatch. The air temperature must also be warm enough for the cold-blooded young grasshoppers to warm themselves sufficiently to move around and eat, building up fat stores. Cool, wet springs are conducive to the growth and spread of pathogens and parasites that feed on grasshopper eggs and nymphs, said Jeff Bradshaw, assistant professor and extension specialist with the University of Nebraska-Lincoln, who is stationed in Scottsbluff.

The cool, wet weather that persisted well into May in many areas of the West wasn’t enough to quell the outbreak of grasshoppers. Bradshaw said producers in Nebraska, especially the northwestern panhandle, weren’t seeing grasshoppers as early as expected, but are still seeing numbers that indicate control is necessary.

Spraying

Franklin recommends that producers start considering chemical control when grasshopper numbers reach 14 adults per square yard. Bradshaw says he considers 25 grasshoppers per square yard to be the threshold at which he recommends chemical control, but that varies by rangeland condition and species of grasshopper. "It’s sort of a complicated beast to really pin down the threshold on, but I guess we do our best," Bradshaw said.

The state of Wyoming gave assistance to four counties last year with their grasshopper outbreak problems. This year, 16 of the 23 counties in Wyoming implemented a grasshopper control program at some level with financial assistance from the state.

The governor of Wyoming set aside $2.7 million for grasshopper control this year. Seven hundred thousand dollars of that was for grasshopper control on state-owned lands. The rest was allocated to Emergency Insect Management Grants that were awarded to weed and pest control districts to help landowners with the financial aspects of grasshopper management. The weed and pest control districts also coordinated landowners with adjoining land so they could aerially spray larger blocks of land, giving landowners a cost break.

Another strategy commonly used in many western states to reduce the amount of spray—and therefore cost—for grasshopper control is reduced area/agent treatments (RAATs). The RAATs program uses a strip-spraying technique, alternating 100- to 150-foot wide swaths of treated and untreated rangeland. Applicators usually mix a pesticide with an attractant, such as canola oil. This lures the grasshoppers from the untreated areas to the treated areas. Most large areas are treated aerially, but some smaller tracts are effectively treated with ATVs, Bradshaw said.

The most commonly used pesticide for grasshopper control is Dimilin, which works by preventing young grasshoppers from molting, or shedding their exoskeleton, killing them in the process. Dimilin is essentially ineffective against adult grasshoppers, so the earlier in the grasshoppers’ life cycle they are sprayed, the more effective it will be, Bradshaw said. "I can’t stress enough the importance of treating grasshoppers while they are still developing," he said. Dimilin is sprayed on foliage that is affected by grasshoppers and must be eaten to affect the insects. This reduces the impact of the pesticide on many beneficial insects, like honeybees, Bradshaw said.

Bradshaw said the best way to tell if it is too late for Dimilin to be effective is to look for flying grasshoppers. "Identifying adults is pretty easy—they have wings. If it’s flying, it’s an adult. There are some species of locusts that don’t have wings as adults, but most western pest species—especially economically important ones—have wings as adults."

He also said that many other insecticides are ineffective against adult grasshoppers and that anything that will kill adult grasshoppers will also kill most other insects it comes into contact with, including beneficial and endangered insects.

Bradshaw says cost, effectiveness and impact are the biggest factors for producers to consider when deciding what pesticide to use for grasshopper control. Some producers may be limited in their control options by the presence of an endangered species or by neighboring agriculture endeavors, such as sunflower or alfalfa fields that rely on beneficial insects and attract honey bees. Some states, he said, encourage honey and fruit producers to register on a website where aerial pesticide applicators can check to see where to avoid when spraying.

Above all, Bradshaw stresses, if producers are making pesticide-related decisions themselves, they should carefully read the labels. The labels tell how long the pesticides are effective, how long animals should be kept off treated rangeland, and other precautions and mixing instructions. Bradshaw also suggests producers talk to their local cooperative extension office for specific information about the grasshoppers and recommended treatment in their areas.

Rangeland health

Sometimes it seems that drought and grasshoppers go hand-in-hand. While warmer, drier weather conditions are beneficial to the health of grasshoppers, sometimes it is simply a case of the grasshoppers having more impact in dry years, Bradshaw said.

"Rangeland has been in pretty good condition this year," Bradshaw said. "That’s going to help a lot in terms of grasshoppers having limited impact on rangeland. Producers really run into trouble when drought or overgrazing cause poor rangeland health. In those situations, you get a lot of competition between grasshoppers and cattle. A lot of the impact the grasshoppers will have depends on the amount of grass you have available and the number of grasshoppers you have to eat it."

Some studies have explored the use of grazing for grasshopper control. Variations in the results correlated with different range type, forage types and grasshopper species, but in general, grazing techniques that encourage healthy, diverse rangeland are most detrimental to grasshopper populations. Removing the foliage that shades the soil—which occurs in overgrazed areas—increases the soil temperature, allows more air movement at ground level, and reduces the relative humidity—all factors that are beneficial to grasshopper emergence and development. Producers can implement grazing plans that take these factors into consideration, and while they may not eliminate a grasshopper problem, they may significantly reduce the impact the grasshoppers have on their bottom line.

Treatment impact

Franklin said the Weed and Pest Districts in Wyoming started spraying with Dimilin at the end of May. They based the decision to do so on field surveys, which are done by going into the fields and counting grasshoppers. As of the first week of July, he estimated that about 90 percent of spraying that was scheduled for grasshopper control in Wyoming had been completed. He said they were seeing some grasshopper numbers drop and were planning to reapply the pesticide in some areas where the application didn’t seem to be effective. "We have definitely seen a reduction in all of the counties that have been treated. Dimilin has a 45-day residual so we hope to continue to see the effects for another month or so in some areas. We are looking at a pretty high success rate right now," Franklin said.

In spite of the success he and landowners all over the West are hoping for, Franklin expects similar grasshopper programs to be necessary again next year. "What we are doing now will help for next year, but there were some areas where we had hatches that were not treated. I think we’re going to see a reduction in eggs laid because of the program. If we do have this program again next year, I expect to see many of the landowners who didn’t sign up for the spray assistance program this year get involved next year."—Maria E. Tussing, WLJ Correspondent

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