Nematodes

Plant-pathogenic nematodes and nematode-management products potentially threaten the long-term sustainability of corn production in Ohio

New problems with plant parasitic nematodes may inadvertently arise with changes in corn production practices, such as no-till, phase-out of several soil-applied insecticides, and continuous corn without crop rotation.  Researchers are providing critically-needed research to address gaps in information and guide cost-effective, environmentally sound nematode management decisions.

Situation

Corn is the most economically important crop in Ohio and the U.S.  In the past 20 years, production practices have changed in ways that promote populations of parasitic nematodes, increasing the potential for yield losses.  Three widespread changes have occurred: the switch to no-till, which favors one class of plant-pathogenic nematodes sensitive to soil disturbance; the removal of soil-applied insecticides that had the added benefit of suppressing parasitic nematodes; and increased corn acreage that is not rotated.

This has led to the development and sale of nematode products, and farmers have become the target of marketing designed to sell products in the absence of unbiased data demonstrating the identities and population densities of nematodes potentially pathogenic to corn.  We don't know the extent of nematode problems, but promoting products without demonstrated need is unwarranted.  Unnecessary chemical use could also harm communities of beneficial nematodes in corn fields.

Response

Research is needed to determine the species and distributions of plant-pathogenic nematodes that occur in corn fields and may be responsible for yield losses under current practices.  Very little research has been done in this area for two related reasons: first, nematodes that attack corn are native species (compared with the soybean cyst nematode, an introduced species on an exotic crop); and second, typical traditional corn production practices such as rotation and tillage kept plant-feeding nematode populations from increasing to damaging levels.  However, very sparse literature suggested that certain species of known pathogenic nematodes had been found in Ohio.

The first step in determining the extent of the nematode threat to corn production statewide, therefore, is to discover the identities and population densities that currently exist.  In 2010, we asked a number of cooperators to submit soil samples from different locations in Ohio to collect the preliminary data for further study.

Impact

Preliminary surveys found plant-parasitic nematodes all samples tested (39 soil and root samples).  The most frequently identified were lesion, spiral and stunt nematodes.  Many lesion and stunt nematode species are pathogens of corn and population densities were high enough to cause yield loss.  Spiral nematodes are generally not threats to corn production, but are anecdotally associated with increased occurrence of non-specific root rots.  Less frequently observed but potentially very damaging were dagger, root-knot, stubby-root, and lance nematodes.  Needle nematodes were extracted from sandy soils at population densities lethal to corn seedlings.

Results document that plant-pathogenic nematodes are ubiquitous in Ohio cornfields and warrant further study to: 1) determine factors affecting nematode population density; 2) establish quantitative relationships between these factors and nematode population densities; 3) model the relationships between nematode populations and yield to develop damage thresholds; and 4) evaluate seed treatments and develop management recommendations.  A key tenet of integrated pest management is that treatment should only be used when there is a documented need, i.e., identification and quantification of the target pest.

This is very important for nematode-management products because of the potential for deleterious effects on beneficial nematodes, with implications for sustainable corn production.

Terry L. Niblack, Anne E. Dorrance, Pierce A. Paul, Department of Plant Pathology