When producers are buying certified wheat seed months ahead of when it will be seeded, they are never sure what the actual planting conditions will be – and/or what pests might be lurking in their fields.
In spring of 2020, as well as in other recent years, one of the main pests found in high numbers throughout Montana wheat were wireworms, the larvae of click beetles.
“When the wheat crop is first getting established is when wireworms do the greatest damage, including significant stand loss,” said Dr. Ruhiyyih Dyrdahl-Young, entomologist and nematologist, and the regional technical rep at BASF.
Wireworms find it easier to move in the soil when the soil is moist in the spring. Stand loss can happen, which leads to missing stalks and lower yields at harvest.
“If the soil is really dried out and crested over, a big worm like a wireworm has a hard time moving through the soil profile,” Dyrdahl-Young said.
But when the soil is moist, the larvae don’t have that problem.
The wireworm has a long life cycle of 5-7 years, and that can increase problems in the field.
“The larvae that hatch out are going to have to survive our harsh Northern Plains winters,” she said.
To survive the winter, wireworms move way down low in the soil to find moisture and warmth.
“These larvae are opportunistic feeders and like to feed on germinating seedlings,” she said, which is why they can be so dangerous to new wheat seedlings.
When the wireworms are in the soil, they are attracted to the CO2 that is put off from a germinating seed.
“The wireworms smell that and move up toward that. They eat the germinating seedlings and attack the roots throughout their growing season,” Dyrdahl-Young explained.
Later on, when wheat starts to tiller, and wireworms attack that growing tiller.
“You will actually see it yellow and die off,” she said
Once wireworms are detected at high densities, the field will remain at high risk for several years.
Wireworms are common in many crops, including winter and spring wheat, particularly when there has been excessive moisture.
More than 80 percent of input salespeople in the Pacific Northwest say wireworms are the biggest pest problems in their area.
“Two adult click beetles in a field in year one grow to more than 200 adults and 1,000 wireworms by year three,” she said. “It is a huge issue in spring wheat and winter wheat in the Pacific Northwest and in Montana, as well.”
Of course, wireworms are found all over the Northern Plains.
Using neonicotinoid seed treatments for wireworms
For crop protection, producers have usedneonicotinoid seed treatments to fight wireworms.
“Neonicotinoids are a systemic insecticide and are in the soil surrounding it, as well, and the insecticide moves up to the foliar part of the plant during the growing season. That doesn’t leave any insecticide down with the seed,” she said.
Dyrdahl-Young called it more of a repellant that briefly repels.
“The coating on the seed repels the wireworm, but the wireworm is still present in the soil. It doesn’t kill the wireworm,” she said.
Using rotations, traps to control wireworms
Other ways producers have controlled wireworms is through rotations and the use of solar bait traps.
To use a solar bait trap:
- Place several traps in the field, both in low spots and high spots.
- Bury 1-2 cups of a 1:1 mixture of corn and wheat to a depth of 4-6 inches.
- Presoaking the whole grain bait one day prior to baiting will increase the bait’s attractiveness to wireworms by promoting seed germination and release of CO2.
- Mound the soil over the top in a dome shape so rainwater runs off.
- Cover the mound with a piece of black plastic (3 square-feet) to promote warming of the soil, so the grain quickly sprouts.
- Wireworms are attracted to the bait grain and will collect to feed.
- Solar bait traps do work, but they are very labor intensive.
New seed treatment coming in 2021
In 2021, BASF is bringing the product Teraxxa, a new type of insecticide seed treatment through the active ingredient, Broflanilide, to Montana, and other states (and Canada).
It will be labeled for use on wheat and other small grains.
“Teraxxa insecticide seed treatment will have a novel mode of action, and only a small amount will kill wireworms, total mortality,” she said. “It is a new weapon to fight wireworms.”
Teraxxa will be released as an insecticide seed treatment, and Teraxxa F4 will be released as an insecticide plus fungicide seed treatment. Teraxxa F4 is currently awaiting EPA registration.
Dyrdahl-Young has several cooperator farm fields in the regions the product will be selling in. While in past years, BASF could take out farmers to the fields, with COVID-19, tours will be different.
“BASF is looking into what we can do for digital plot tours so farmers can see how Teraxxa is working in small grain fields,” she said.
In addition, North Dakota State University is conducting studies on Teraxxa.
For more information on Teraxxa, see your local BASF dealer, or for more information on wireworms, see https://agresearch.montana.edu/warc/research_current/WirewormMgmt.html.