Corn nematode survey results

by Deborah Jeanne Sergeant

Corn nematodes negatively affect corn yields. Mike Stanyard, Cornell Cooperative Extension Northwestern New York Team, presented “Corn Nematode Survey Results: Management Implications?” at the recent Corn Congress, presented virtually by Cornell University.

A nematode is a microscopic roundworm. Of them, 15% are plant-parasitic. Most are not beneficial and a few can be detrimental.

Plant-parasitic nematodes have a spear-like stylet. “It can shoot out like a mosquito or how an aphid would feed on a plant,” Stanyard said.

Just rotating crops will not always deplete their numbers to safe levels. Sufficient levels to harm crops depend upon the species of nematode.

While the damage of many pests is easy to spot, that’s not always the case with harmful nematodes. “It’s very hard to look at a field and say ‘I have corn nematode damage,’ as you can’t see them,” Stanyard said. “Perception is reality. It’s not like you can pull up a plant and see seed corn maggot.”

Nematode damage can resemble insect, disease or herbicide injury, fertility issues or soil factors. Stanyard said nematode damage often manifests with patchiness, as nematodes spread through soil movement. “Tillage, harvest and planting is how they spread,” Stanyard said. The damage can “look like compaction, herbicide injury or drift issues,” he added.

The nematodes that predominantly feed on corn in Iowa are Pin, Ring, Root-knot, Spiral and Stunt (low levels of potential damage); Dagger, Lance, Root-lesion and Stubby-root (moderate levels of potential damage); and Needle, Sheath and Sting (high levels of damage).

“Needle and Sting I was worried about finding in New York,” Stanyard said. “These are the largest of the nematodes. One per half cup of soil is the threshold. These like highly sandy soils and we have some of these in New York.”

Stanyard said current production practices that favor nematodes include increased use of GMOs to manage insects instead of chemicals that may have suppressed nematodes; an increase in no-till acres; and an increase of corn-on-corn planting. “I think we’ve seen more prominence of this pest because of the cultural and planting things we’re doing,” Stanyard said. “These things feed on other green tissue than corn which helps them survive corn-to-corn and corn-to-soybeans.”

Farmers should also be wary of equipment coming from different farms, as their equipment must be cleaned properly to avoid transferring nematodes through machinery.

Since there were no surveys on nematodes done in New York, Stanyard undertook the project across nine counties, from Niagara to Seneca.

Stanyard took 20 samples per plant in the vegetative state up to tassel (V6 – V12) from among 45 sites. The soil probe was angled beneath the plant roots eight to nine inches.

What he found was Dagger, Lesion, Pin, Root-knot, Spiral and Stunt. “All six were on the list,” Stanyard said. “I was also worried we’d find a new one they didn’t have in the Midwest, but these are the same old players. The worst two on this list are Dagger and Lesion and these are the moderate damage potential. The rest are low in their impact on corn.”

He found Lesion in 38 fields, Spiral in 29, Stunt in 18, Root-knot in seven, Pin in four and Dagger in one. Every soil sample had at least one nematode, but not all were at concerning levels. He said the survey confirmed the presence of corn nematodes in New York. A few fields were above established threshold. Sixty-four percent of the fields had more than one species and 38% of them had more than two. But Stanyard did not find the worst species.

“We definitely have corn nematodes in northwestern New York, and I suspect if my colleagues did this in other parts of New York they’d find the same species,” Stanyard said. “We do have these nematodes – six were above the established thresholds. They can get to a point where something will have to be done in subsequent years.”

He said the next questions that require answering include: What is the cumulative effect of multiple nematode species feeding in corn? Is nematode feeding yield limiting? Are nematode treatments effective?

“We want to look at nematode treatments, if they’re effective,” he said. “We need to do some field trials. What kind of yield loss are we seeing? If anyone’s interested in doing field trials, let me know.”

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