AMES, Iowa –University entomologists and plant pathologists are advising farmers to monitor their fields for invasive insects this upcoming planting and growing season, including scouting and soil sampling.

“We have the ‘usual suspects,” said Erin Hodgson, Iowa State University professor of entomology and extension entomologist. “Western and northern corn rootworm populations seemed to be higher this past year than the last couple of years. Some fields experienced severe root injury, and storms caused stalks to lodge in some fields,” she added.

She said potato leafhoppers, which are migratory insects, also showed up in big numbers last summer.

“Some alfalfa and soybean fields had notable feeding injury; drought likely made the stress more visible,” she said.

She said fall armyworm is another migratory insect from the southern U.S. that arrives at harvest.

“A mild winter, combined with violent storms in the south, generated a large number of moths moving to the Midwest,” she said.

She said unprecedented caterpillar activity was observed in field crops, pastures, and turf.

“The moderate fall temperatures allowed caterpillars to be persistent well into October,” she said. “Fall armyworms can’t survive in Iowa, so we will have to wait until this next growing season to see if they show up in the same numbers.”

According to Purdue University Entomologists Christian Krupke and John Obermeyer, reports last August of denuded (stripped) forage crops – especially alfalfa – from large numbers of fall armyworms have been shared from throughout Kentucky, and southern counties of Indiana and Illinois.

“It’s an outbreak pest,” said Kevin Rice, University of Missouri Extension entomologist during the university’s annual crop management conference last November. He said farmers should expect an influx in armyworms every 30 to 50 years, with many wondering if there will be a repeat in 2022.

Chris Hicks, University of Tennessee Extension Smith County director, said fall armyworms devastated fields in West Tennessee and parts of lower Middle Tennessee last summer, and made their way to Smith County last fall.

“Fall armyworms can be identified by the damage they leave behind, as well as the presence of a prominent, light-colored inverted “Y” on their relatively dark head,” he said. “They are ferocious eaters that feed on grass, fresh sod, soybeans, and several uncultivated plants.

“An armyworm’s life span is about twelve days, with the last couple of days being the period where armyworms eat the most,” he said. “Overnight, they can turn a beautiful green lawn or freshly seeded pasture into a barren, brown field of destroyed grass.”

Another crop pest that is likely to show up in 2022 is the soybean cyst nematode. It reproduces best in hot, dry soils, said Greg Tylka, Iowa State University professor of plant pathology and microbiology.

“Obviously, soils in much of Iowa were very dry in 2021, so I expect that the dry weather, coupled with the loss of effectiveness of common soybean cyst nematode resistance (PI 88788) resulted in very large increases in soybean cyst nematode numbers in infested fields throughout Iowa in 2021,” he said.

He said fall soil samples are a great way for farmers to check fields for soybean cyst nematode.

“Fields in which soybeans will be grown in 2022 should be sampled in the fall or in early spring of 2022 – after the snow melts and the soil drains a bit – for the presence of soybean cyst nematode,” he said.

Once the soybean crop is planted, adult soybean cyst nematode females can be seen as small, round, white objects on the roots of infected soybean roots, he said.

“To check for soybean cyst nematode this way, roots should be dug from the soil, and the soil should be carefully crumbled away from the roots to reveal the soybean cyst nematode females, if present,” he said. “This can be done as soon as five or six weeks after planting, all the way through mid-August.”

He said field research experiment results revealed very high numbers in soil samples collected at the time of harvest in 2021.

Katie Parker, University of Illinois Extension local foods and small farms educator, said entomologists determined fall armyworm numbers last year were the highest they had been in Illinois in 30 years.

“Scouting in the cool part of the day when the caterpillars are actively feeding will allow farmers to determine the size and number of fall armyworms, which will help decide control strategies,” she said.

“If you are not scouting when caterpillars are actively feeding, you will need to look deeper into the canopy either by parting grass, or using a sweep net,” she added.

She said insecticide applications are not usually economical for control of fall armyworms; however, infestations of three or more caterpillars per square foot may justify an insecticide application.

“Fall armyworm is best controlled when caterpillars are 1/2” or smaller,” she said. “Pyrethroid insecticides provide effective control. If used, it is best to make applications early in the morning or later in the evening when larvae are most active.”