It is quite common to find nematode species that feed on corn in low numbers throughout the Corn Belt, says Tylka. Much is still unknown about how much yield loss they cause and what population levels trigger measurable yield loss. Better early season weed control might help to prevent parasitic nematodes from ever reaching damaging levels in corn.

“In Iowa, if you harvest an area with only 160-bu. corn when you were expecting 180 bu., you wouldn’t know whether nematodes were the problem without scouting and sampling soil and roots earlier in the year,” says Tylka. “For nematodes that feed on corn, all but needle and sting species are more yield nibblers than yield chompers. So, these nematodes haven’t been on most people’s radar screen yet.”

 Bird advises keeping a year-by-year record of what your corn yields are and where problem areas of the fields are located. “Then, sample soil and root samples for nematodes there.”

In Michigan, one particular root-lesion nematode, Pratylenchus penetrans, causes the most concern to overall corn yields, says Bird. “Root-lesion nematodes probably take 5 bu./acre off the top of all the corn grown in the state,” he says. “They are present in all soil types but are more of a problem on sandy, coarse soils.”

Root-lesion nematodes have a very wide host range, so they’re also difficult to control through crop rotation, he adds. “In four decades, I haven’t found a non-host crop,” says Bird.

Since root-lesion nematodes live inside the roots, include some root material with soil-core samples when sending them to a lab for analysis, he says.

There are different recommendations on when to scout for nematodes that feed on corn, and what samples to take, says Tamra Jackson, University of Nebraska-Lincoln (UNL) Extension plant pathologist. “Check with your local nematology lab.

“In Nebraska, we have documented areas with problems from sting and needle nematodes, which is why we recommend soil sampling in spring, rather than later in the year when some nematodes may have traveled deeper in the soil, beyond our soil probes,” says Jackson. “For most other nematodes, it’s okay to sample later in the season.”

Root-lesion nematodes are present in 93% of Nebraska fields, says Jackson. “Cumulatively, they are the most common and probably cause the most damage,” she says.

If soil and root samples show a significant problem with parasitic nematodes that feed on corn, you’ll have to wait until another year begins to start a control program, Tylka says. “There are no in-season tactics to mitigate yield loss in the current growing season,” he states. “Primary management strategies for future years are soil-applied Counter 15G and 20G nematicides and/or seed treatments such as Avictaand Votivo.”

Nebraska has limited results from studies on nematicidal soil and seed treatments for corn, which have been published on the UNL Plant Disease Central website under Management Trials for Corn, Jackson says.

Control products have had the greatest return in areas of greatest nematode pressure,” she says. “However, none of these products will entirely eliminate the problem. Once you have nematodes in corn, it becomes a chronic problem because we don’t have a way to eradicate them.”