URBANAThe search for the cause of early season damage to a corn crop rarely includes submitting a soil sample for nematode analysis since it is widely believed damaging levels of nematodes rarely occur in fine-textured soils.
But, according to a recent survey in northwestern Illinois by integrated pest management and crops educators from University of Illinois Extension, nematodes can cause early season problems irrespective of soil type.
The educators teamed with commercial fertilizer dealers and other Extension personnel to be part of the team collecting soil samples, said Dave Feltes, IPM educator at the East Moline Center. Forty-eight composite samples were collected from Whiteside, Henry, Brown, Bureau, Henderson, Menard and Hancock Counties and submitted for analysis. Both sandy and
fine-textured soils were sampled.
For all soil samples, the population of each nematode species was rated as insignificant, minimal, moderate, severe, or very severe in terms of the amount of damage they could cause to a corn crop.
Ratings of severe and very severe can cause corn yield losses of 50 percent or more, depending on soil and environmental conditions, Feltes said. The results indicated that 79 percent of the samples were positive for soybean cyst nematode.
He notes that 90 percent of the samples were positive for spiral nematodes with three of the 43 positive samples rated severe and four of the samples rated moderate in the amount of damage they could cause to a corn crop.
In addition, 54 percent of the samples were positive for lesion nematodes with 5 percent of the samples rated very severe or severe in the amount of damage they could cause to a corn crop, Feltes said. About 52 percent of the samples were positive for stunt nematodes with all levels rated as causing minimal damage to a corn crop.
The samples also showed lesser amounts of lance and dagger nematodes, with only a small portion at levels that would cause moderate or severe damage. Many of the samples showed the presence of more than one species of nematodes.
This survey clearly points out that when damage to a corn crop occurs early in the season on coarse- or fine-textured soils, nematodes should not be discounted as the cause of damage, Feltes said. Nematode damage can be additive, meaning that if a farm has more than one species of nematode present, the amount of damage caused would be increased.
Feltes points out that soil sampling and nematode analysis are necessary for a grower to determine which nematode species are present and at what levels.
Once a nematode problem is recognized, there are several options that growers can employ to help manage damaging nematode populations, including crop rotation, moldboard plowing, and soil-applied insecticides or nematocides, for which only a very limited number of products remain available Feltes said.