A 10-year summary of testing for corn nematodes
click image to zoomFrom Tylka et al. 2011. Testing for Plant-parasitic Nematodes that Feed on Corn in Iowa 2000-2010. Plant Health Progress doi:10.1094/PHP-2011-1205-01-RS. Figure 2. Number of damaging population densities of plant-parasitic nematodes on corn from samples submitted to the ISU Plant and Insect Diagnostic Clinic from 2000 to 2010, by county. Implications of the results
It was not surprising that most samples contained one or more species of nematodes that feed on corn. Most of these nematodes are likely native to Iowa and fed upon native plants before corn was cultivated as a crop. The nematodes are not specific to corn. They are very commonly found at low population densities not thought to be damaging to corn.
The high concentration of damaging populations of needle nematodes in Muscatine County is likely because needle nematode is damaging at very low population densities (basically at the detection level of one worm per 100 cc soil) and because of the high prevalence of sandy soils in that area of Iowa. (Needle nematode occurs only in soils with at least 49 percent sand).
One should not extrapolate the summarized results to counties from which no nematode samples were submitted for testing.
The total number of samples tested for plant-parasitic nematodes that feed on corn from 2000 to 2010 was extremely low considering there are more than 13 million acres of corn grown in the state. There were 77 samples submitted to the ISU Plant and Insect Diagnostic Clinic in 2011 for nematodes that feed on corn.
It is not likely that healthy-looking corn is being damaged by plant-parasitic nematodes. So, not every field in the state needs to be sampled for nematodes that feed on corn. But significantly more cornfields showing symptoms of stress should be checked for plant-parasitic nematodes. The ideal sampling times and methods for nematodes that feed on corn were discussed in an earlier article in ICM News.
Increased sampling for nematodes that feed on corn will lead to a better understanding of the importance of these native nematode pests in corn production in Iowa. And information from such samples will allow farmers and those who advise them make more informed decisions concerning the use of current and future nematode management products.