How to Manage Nematodes in Corn
So what’s wrong with this field? Compaction? Herbicide damage? Early-season cutworms? Could be all three. In this case, though, the culprits were nematodes that feed on corn.
You may think corn nematodes are a new pest, but they aren’t. Most are native to the United States, and long resided in soils before European settlers arrived. These roundworms, of which there are thousands of species, are survivors. “The last thing to die off this planet will be cockroaches and roundworms,” says Glen Dappen, a retired professor of biology at Nebraska Wesleyan University.
Nematodes infest about anything, including corn. Many nematodes are benign. In corn, though, there are species that can inflict heavy yield damage. “In corn, nematode damage is frequently misdiagnosed,” says Dappen. Besides stunted plants shown in this slide, afflicted plants often show small ears and kernels later in the season. “The ears will not fill out,” says Dappen. “It’s just like the corn plant ran out of gas.”
The seemingly sudden rise in nematodes in corn, like the lesion nematode pictured, is tied to three factors:
- More conservation tillage.
- Few carbamate and organophosphate insecticides.
- More continuous corn
Carbamate and organophosphate insecticides kill nematodes, in addition to corn rootworm. Meanwhile, more conservation tillage and continuous corn mimic the undisturbed prairie in which nematodes thrived.
Most species of nematodes are not damaging to corn until they reach a certain number. That’s referred to as a damage threshold, says Greg Tylka, Iowa State University Extension nematologist. Damage thresholds vary between species. Lance nematodes (pictured) have damage thresholds from 300 to 400 per 100 cubic centimeters of soil. Others, like needle, have a damage threshold of 1 per 100 cc of soil.
Knowing what type of nematodes you’re dealing with is key to managing corn nematode. Sampling can start in mid-season (now), as that is when most corn nematode populations are peaking. Spring sampling isn’t recommended.
That’s because you can’t predict if nematodes will increase to damaging levels if you sample early in spring. Sample 12 inches deep, as some nematodes only being showing up in the bottom 8 to 10 inches. Collect up to 20 cores from a field and include root samples, too, says Tylka.
There are a couple exceptions to this sampling time, though—needle and sting nematodes, says Tylka. These are the largest and most damaging of all nematodes that feed on corn. They’re found only in soils with more than 70% sand. Sampling should occur in spring and fall, rather than mid-season. That’s because they migrate deep in the soil during the growing season.
Suppose your samples come back showing you have nematodes above damage thresholds. Unlike soybeans resistant to SCN, no corn hybrids resistant to nematodes exist, says Tylka. Counter, an organophosphate insecticide aimed at corn rootworm, is also labeled for nematodes in corn.
A couple new seed treatments have recently appeared on the market, says Tylka. They are Avicta Complete Corn from Syngenta and Poncho/Votivo from Bayer Crop Science. Avicta Complete Corn contains a nematicide that kills nematodes. Poncho/Votivo contains a biological compound that forms a protective barrier across corn roots that helps halt nematodes from feeding on corn roots.