Surprised is the word that best describes Leon Knirk’s reaction when he saw the results from 22 soil samples he pulled from his corn fields this past summer.
Every sample contained the microscopic pests known as corn nematodes.
"They can take a chunk out of your corn yield potential without you knowing it," says Knirk, who farms near Quincy in south-central Michigan.
Yield reductions of less than 10 bu. per acre are typical of corn nematode pressure, though losses can reach 100% in extreme cases.
Based on the laboratory risk index used, 68% of the samples from Knirk’s corn fields contained nematode levels and/or species presenting moderate risk levels; only 32% of the samples were low-risk.
Farm Journal Associate Field Agronomist Missy Bauer adds that 100% of Knirk’s soil samples contained lesion nematodes and 64% contained dagger nematodes. Both species can cause low to moderate levels of damage to corn.
Of the 60-plus nematode species, about 12 are damaging to corn. The needle nematode can cause yield losses exceeding 60%, according to University of Illinois Extension research.
One or more nematode species is present in every soil type across the Corn Belt. Damage appears to be on the upswing, notes Bauer, who serves as Knirk’s Ultimate Farm Quest agronomic specialist. This trend is due to corn-on-corn rotation, reduced tillage and the use of new pyrethroid products that don’t control nematodes.
Knirk’s history of using manure to boost fertility levels and the fact that his soils are light and sandy are additional reasons Bauer believes all his samples were positive for the pest.
"I’d caution farmers that we have seen damaging levels of nematodes in heavy soils, too," she notes.
Of the 366 soil samples Bauer took from corn fields across 20 Michigan counties in 2010, 97.5% contained corn nematode species. The research was funded by a grant from the Corn Marketing Program of Michigan.
Bauer says that nematodes go undetected in corn fields because the damage they cause looks similar to nutrient deficiency, insect feeding, herbicide injury, disease or compaction.
The timing for visible nematode damage is similar, too.
"Roughly four to six weeks after planting is when you can first notice a problem," Bauer says. "At that point, farmers have no course of action to control the pests."
Start now. To get ahead of nematodes, Bauer tells farmers, address potential infestations during winter.
"Touch base with the laboratory you want to work with now; they may have some specific directions for you to use this spring when taking samples to establish base levels," she says.
If you have a known history of corn nematodes in fields, take pre-emptive measures for control this spring.
Avicta Complete Corn from Syngenta is a seed treatment fungicide that offers protection against nematodes during germination and stand establishment.
Bayer CropScience Poncho/Votivo biological seed treatment protects corn plant roots so nematodes have limited or no ability to feed.
Take note that if your product label does not spell out that it controls corn nematodes, it probably doesn’t.
Iowa State University Extension offers additional recommendations to minimize the impact of corn nematodes: Maintain good fertility levels; know that nutrient-deficient plants are more susceptible to injury; and control weeds because some of them host various nematode species.