Corn yield loss to nematodes generally has not been a major consideration in eastern Virginia. However, there are some indications nematode populations are shifting and/or increasing, and injury to corn might be increasing.
Increases in nematode populations are possible with farming practices that include: Conversion to continuous no-till, changes in corn genetics, and the conversion from in-furrow insecticide/nematicide treatments to seed-applied treatments in corn.
The Virginia Corn Board provided funding to Virginia Cooperative Extension to conduct a nematode survey in 2007 and 2008, and 150 samples from fields with some type of production problem from 21 counties in eastern Virginia were submitted.
Over the two years, based on current nematode thresholds and recommendations, 45 (30 percent) of the samples indicated a nematode problem, while 38 (39 percent) samples indicated a possible nematode problem.
Stubby root and lance were the most common nematode species found. Lesion nematodes were fairly common, while root-knot and dagger were less common.
Damaging levels of sting nematode, a species that can cause significant yield loss in sandy soils, were found in several samples from Southampton County.
Given our current nematode thresholds, our survey indicates that nematodes are causing some yield loss in some corn fields.
We hope to conduct more work in 2009, including the evaluation of seed-applied nematicides, tracking nematode populations in identified problem fields, and root assays. Producers who suspect a nematode problem are encouraged to contact their local Extension agent or agricultural supplier so that soil samples and/or root samples can be submitted for a definite diagnosis.
The best time to take soil samples for diagnostic assays in corn is June and July.
If you are interested in a copy of the complete results from either survey, please contact Keith Balderson at the Essex County Extension Office at 804 443-3551 or email@example.com.