The widely held belief that damaging levels of nematodes rarely occur in fine-textured soils may be proving wrong.
According to a recent northwestern Illinois survey, nematodes can cause early season problems irrespective of soil type. So say integrated pest management and crops educators from University of Illinois extension.
“The educators teamed with commercial fertilizer dealers and other extension personnel to be part of the team collecting soil samples,” says 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.”
With 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% or more, depending on soil and environmental conditions,” Feltes says. “The results indicated that 79% of the samples were positive for soybean cyst nematode.”
He notes that 90% of the samples were positive for spiral nematode, 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% of the samples were positive for lesion nematodes, with 5% of the samples rated very severe or severe in the amount of damage they could cause to a corn crop,” Feltes adds. “About 52% of the samples were positive for stunt nematodes and all levels rated as causing minimal damage to a corn crop.”
The samples also showed lesser amounts of lance and dagger nematodes. Only a small portion were 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 says. “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. They include crop rotation, moldboard plowing, and soil-applied insecticides or nematicides, for which only a very limited number of products remain available” Feltes says.