Legionnaires legionnaires: Stay vigilant in 2022

It’s no secret that farmers saw more crop damage from army worms last fall than in previous years due to intense pest pressure. So what is the forecast for armyworm damage in the 2022 growing season? It’s too early to tell exactly, but you can study what to look for and how to handle it.

First, know your army worms. Six different types of armyworm species exist, says Nick Seiter, an entomologist at the University of Illinois. But only two of the six are generally pests for Illinois farmers: true armyworm and fall armyworm. The two hit at different times of the year.

True army caterpillar

The true armyworm is the first species farmers will see during the growing season. These butterflies start flying as close as the southern tip of Illinois once nighttime temperatures reach around 50 degrees F, or early to mid-April, Seiter says. The damage caused by these insects will begin to be visible in May and will mainly target corn plants.

Look for moths in fields with weeds or cover crop residue. They like to lay their eggs in dense, grassy vegetation. From there, the army worms will move into the corn plants and cause stand problems.

What is the projection of true army worm pressure as spring and summer approach?

“We try to project insect pressure every year, and every time it seems to fail,” Seiter says with a laugh. Last winter was not unusually cold. There haven’t been many ice storms or harsh conditions that could bring insect populations down, but that doesn’t guarantee high insect pressure either.

“The true army worm is an insect that not much is known about because there isn’t much foreshadowing from the south as to when it will arrive,” says Seiter. That’s why Kelly Estes, Agricultural Pest Survey Coordinator at the U of I, leads the Moth trapping network to coordinate with farmers who volunteer to monitor moth traps in their fields from April 1 to May 31. This effort measures the number of moths in Illinois and predicts intensity.

Once the moths have laid their eggs, farmers can have trouble spotting the larvae due to the nature of the insect, Seiter says. Nuisance caterpillars tend to be nocturnal, feeding at dusk and dawn to protect themselves from birds. But farmers can still search for the true army worm.

“If you’re looking for the insect in your field, you have to dig through vegetation and residue. Often you can find them on the underside of a corn leaf,” he says. “But you’re also going to see their damage – little bits of chewing on the leaf tissue.”

Once damage is identified, be sure to apply insecticides accordingly.

“If you get to a point where you have 2% to 3% of the corn stands at risk, then it might be worth spraying the population with a pyrethroid insecticide in 10 to 15 gallons of water volume to make sure that ‘it gets into the soil where the larvae could hide,” says Seiter. It’s an effective control method if farmers spray the fields in time. That’s when data from the traps can help farmers to determine the critical time of application, which generally occurs between mid-May and late May.

fall armyworm

Illinois farmers won’t soon forget the fall armyworm infestation of 2021, when the pest devastated stands of alfalfa and more.

Seiter says farmers in Illinois don’t always deal with fall armyworm damage — sometimes it’s five to 10 years between incidents like 2021. Either way, the armyworm fall moth is a species similar to the true armyworm, damaging corn plants and pastures.

So how do farmers anticipate whether FAW will hit Illinois or not? Fortunately, Illinois farmers have more information about this species because the insects overwinter in southern regions such as Texas, Florida, Mexico and Central America, he adds, adding that typical fall armyworm spots will begin to occur in mid to late August. .

“The Fall Armyworm moves north with each successive generation throughout the year,” says Seiter. “Generally, if it’s going to be a problem in Illinois, it’s already been a problem in states like Arkansas and Tennessee.”

That’s lucky for growers in Illinois because the fall armyworm is hard to spot as the true armyworm, he adds. It’s not impossible, but you have to be prepared.

“The FAW is a sporadic insect, making the vast majority of its diet in a relatively short period of time – typically the last two to four days of its life cycle,” says Seiter. If you’re not there to check the fields frequently, you might not see any damage, then all of a sudden you’ll check the field again, and it will be gone because the FAW took over. above.

Long story short, staying up to date with extension reports from Southern states might be your best tool for knowing when to watch for FAW, he adds. In June and July, crop specialists will have a better projection of FAW pressure in Illinois.

When it comes to FAW management, Seiter says the strategy depends on your economic situation and pressure.

“If you’re about to cut hay, going ahead and cutting early is often an effective management strategy because you’re getting the hay out of the field before the larvae eat it,” he explains. “If you are earlier in the hay season, you can use pyrethroid insecticides.”

You need to react quickly when you see larvae. Applications will be most effective when you find the small larvae early on, whether in a cornfield or pasture, Seiter says.

In addition to pyrethroid insecticides, consider alternatives to non-pyrethroid insecticides such as insect growth regulators and diamide insecticides. These alternatives tend to be more expensive, but the effectiveness of the products is higher.

Helps monitor spring butterflies

Want to help predict army worms? Consider joining the University of Illinois Moth Trapping Network.

The program helps monitor black cutworm and true armyworm to help project the insects’ arrival and predict when damage might occur in Illinois, Seiter says.

Here’s how the program works:

  • Install the traps provided.
  • Monitor the traps regularly from April 1 to May 31. Verifications must take place every other day, or at least on Monday, Wednesday and Friday of each week.
  • Use an identification guide provided to detect moths caught in the traps.
  • Report moths caught in traps via the website or by email.

For more details or to register for the program, email Kelly Estes at [email protected].

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