There's no getting around it: A wide variety of corn nematodes exist and each have their quirks.
Some burrow in the roots and can only be found there during sampling, while others live in the soil. Some leave evidence of their destruction above ground, some only leave a trail on roots.
Tim Todd, a research nematologist with Kansas State University, told attendees at the Conservation Tillage Conference in Morton, Minn., recently that growers need to understand nematodes to manage them.
There is no commercial resistance, he says. Crop rotation is a good choice to control populations, but plants in a rotation could be a good host. In general, a corn-soybean rotation is preferable to continuous corn and will give the grower some management control.
Weeds and cover crops could also be a good host to nematodes.
"You have to be concerned about host status," he says.
Growers can focus their defense strategy on fertility maintenance. Healthy crops have a higher tolerance.
Reduced tillage may spread other pests, like soybean cyst nematode, but that's not a concern with corn nematodes. They are in every field already. However, reduced-tillage producers should be aware that some corn nematodes are sensitive to soil movement and research suggests no-till or strip till may actually increase corn nematode populations.
"No-till is not going to help you. It could make things worse," he says.
But this shouldn't be a great concern. He says the agronomic benefits of reduced tillage outweigh the problems it could cause in nematode numbers.
Soil type will affect which nematodes are in a field. The types of nematodes that cause the most severe damage, the sting and needle nematodes, only occur in soils with 80% to 85% sand. They can be found in the sand hills of Nebraska and Kansas. Todd couldn't recall any sting nematodes ever reported in Minnesota.
Still, the nematodes that live in moderate, heavy or textured soils can cause yield losses, so sampling is important, he says.
Those capable of moderate damage, such as stubby-root or lesion, are more prevalent than the severe-risk nematodes. Lesion nematodes are the most common group in Midwest corn fields. He also classified some nematodes as "low or undetermined risk."
He recommended producers monitor fields on a regular basis to keep a recorded history of population levels. His favorite sampling time is early in the growing season, within 4 to 6 weeks of planting. This is when sampling can diagnose whether or not a nematode problem exists.
Harvest is the most popular sampling time, but Todd warns nematode damage will already be done by then and population levels may not tell the whole story of how many nematodes were in the field that year.
Damage and economic threshold levels aren't set for corn nematode species because it varies with different conditions. He suggests producers compare their population to nearby areas.
If producers see plant damage, laboratory testing on root zone samples can determine if nematodes are the culprit. It's important to sample around a damaged area, not in it, because the nematodes will have moved on.
Advisory sampling is a tool growers may use to factor in their nematode number in management decisions. This requires collecting soil core samples. Todd told producers to take samples in a systematic way by using patterns, such as a zig-zag, to get reliable results. Growers should find a lab they like working with and stick with it to get consistent data.
He notes that beneficial nematodes exist that feed on bacteria and fungi while contributing to the soil ecology. The old nematicide compounds affected both good and bad nematodes, but he doesn't know how new compounds will affect the beneficial roundworms.