Nematodes are microscopic worm-like soil organisms that, depending on the species, can either benefit or harm the growth and development of corn. Their effect on corn roots are garnering more attention as the harmful species are being discovered in more cornfields throughout the Midwest, says Terry Niblack, a nematologist and chair of Ohio State's Department of Plant Pathology.
Plant-parasitic nematodes can be a problem for corn yields because they feed on corn roots and reduce root growth. Their root feeding reduces the plants' ability to uptake nutrients and water, and can also encourage bacterial and fungal pathogens to enter the plant, she says.
"When present and in high numbers, these worms that feed on the roots of the corn plant can indeed cause considerable yield loss," says Niblack. "However, losses due to nematodes often may go undetected or may be attributed to other causes.
"In corn, nematode problems are usually very difficult to detect because these pathogens usually cause uneven growth, without any clear above-ground symptoms."
While it is unclear if there is a nematode problem in Ohio corn, surveys done in other Midwest states have found the organisms to be numerous and problematic in some cases, depending on the species.
Niblack, who was a professor in the Department of Crop Science at the University of Illinois until last summer, conducted one such survey of more than 550 cornfields in Illinois. She found nematodes in every field at populations ranging from 100 to more than 4,000 nematodes per 100 cubic centimeters of soil.
Even if researchers discover similar findings in Ohio cornfields, Niblack cautions that studies need to be done to determine population levels and damage thresholds under conditions in Ohio.
"However, even without a survey, several of our current crop management practices favor potential nematode problems," she says.
That includes the widely used no-till or conservation tillage, corn-on-corn cropping systems, and the abandonment of soil-applied insecticides, which in the past provided the added benefit of controlling nematodes, Niblack says.
"So, while we wait for resources to conduct field surveys across the state of Ohio, we can use our understanding of the biology of these pathogens to make a projection as to where nematodes are most likely to be a concern and start using management practices for minimizing losses caused by these organisms," she says.
Nematodes are most likely to cause problems in no-till, corn-on-corn fields, so crop rotation and tillage might be the best approaches for minimizing problems. Because reasonable recommendations depend on identifying which nematodes are present, decisions about management should be based on the results of a soil sample analysis.
Farmers can send soil samples to the C. Wayne Ellett Plant and Pest Diagnostic Clinic at Ohio State (http://ppdc.osu.edu), where experts can identify the nematodes, Niblack says.
"Further research is needed in order to provide other management recommendations, such as seed treatments and hybrid resistance or tolerance," she says. "The effect of seed treatment nematicides on nematode population is unknown, and trials from other states have shown variable yield responses to these products among locations and hybrids."