Survey of Nematode Populations and Prevalence in Virginia Corn and Soybean Fields.

Reports of nematode damage in eastern Virginia corn and soybean fields have increased in recent years. Shifts in nematode populations are expected with farming practices that include: conversion to continuous no-till; repeated planting of varieties with single-gene resistance to soybean cyst nematode; less wheat in the crop rotation; changes in corn and soybean genetics; conversion from in-furrow insecticide/nematicide treatments to seed-applied treatments in corn. 174 samples (107 soybean/67 corn) were taken from the root zone during the growing season (corn: early July, soybean: mid-August-mid-September) of 2007 in fields with a history of poor growth. Production information, along with GPS coordinates, was gathered and recorded with each sample. Populations high enough to adversely affect yields and warrant control measures were found in over 47% of the soybean fields and in nearly 35% of the corn fields. Another 24% of the soybean and 37% of corn fields were identified with borderline-damaging populations. The most common nematodes found in soybeans were lesion, cyst (SCN), stunt, and root-knot (RKN). The most common found in corn were stubby root, lance and sting. 27% of the soybean samples were found to have SCN. Most current soybean varieties with SCN resistance have that resistance to Races 3 & 14. Further sampling of fields with SCN ensued to determine nematode race; results of those determinations will be forthcoming. In corn, 54% of the samples had stubby root nematode numbers, and 40% had Lance nematode numbers at levels high enough to be considered problematic. This survey suggests that further study is needed to determine the level of susceptibility and tolerance of currently grown soybean varieties and corn hybrids. Of particular concern is the lack of root-knot resistance in corn hybrids and the possible shift from Race 3 and 14 nematodes (current varieties have resistance) to races of nematodes that cannot be controlled with current cyst nematode resistant soybean varieties. The survey was repeated in 2008.