If you think you have a nematode problem, dig some plants and study the roots. Then have your soil and roots analyzed, advises Missy Bauer.
You can manage them, if you know what to look for
Drought across much of the Corn Belt in 2011 might have allowed nematodes to make a bigger-than-usual impact in some corn fields.
"Due to dry conditions, in spots where we knew nematodes were present, the damage was more visible than usual," says Farm Journal Field Agronomist Ken Ferrie. "Nematodes damage a plant’s root system and reduce its ability to respond to stress. So, instead of the usual 5 bu. to 10 bu. yield loss caused by nematodes, some fields suffered a 40 bu. to 50 bu. loss."
About 25 to 30 species of nematodes that feed on corn have been identified in Midwestern U.S. surveys, suggesting that the populations of such nematodes might be increasing, perhaps in
response to more continuous corn and reduced use of organophosphate and carbamate soil insecticides.
"In recent Illinois surveys, we found lesion nematodes in 80% of corn fields," says Ohio State University plant pathologist Terry Niblack (formerly with the University of Illinois). "About two-thirds were at population densities that would be considered harmful."
Not everyone agrees on how serious a threat nematodes pose to corn growers. However, pest authorities do agree that if nematodes are a problem in your fields, they can be managed.
Control measures, they add, must be tailored to your soils, crops and nematode species and grounded on advice from local experts.
|Damaged roots might have a stopped-off or club-shaped appearance. The tips might turn brown and stop growing. You may also see root rotting.
What’s the risk? No one disputes that, under the right circumstances, nematodes can trim corn yields. Farm Journal Associate Field Agronomist Missy Bauer has documented 70% yield loss in hot spots under severe nematode pressure.
But Iowa State University nematologist Greg Tylka believes the most severe losses are limited to isolated areas, when nematode feeding is compounded by other stresses such as drought or soil compaction. An exception involves sting and needle nematodes, which occur only in soils with at least 70% sand and almost always cause yield loss.
Bauer, who says she finds nematode damage (often misdiagnosed as something else, such as herbicide injury) on many field calls, is more concerned. "Even if you don’t farm sandy soil, there are other species, such as lesion and dagger nematodes, which can reduce yield," she says.
Bauer works in southern Michigan, northeastern Indiana and northern Ohio. Tylka emphasizes that his observations are limited to Iowa—and he notes that his predecessor, Don Norton, did document corn yield losses from nematodes present in loam and silt loam soils.
"Because there are so many species, and so many conditions, which affect the species in various ways, nematode biology and management is much more localized than most other aspects of crop production," Tylka explains. "Any measures a farmer takes must be based on advice from local experts."
Southern nematodes. For Southern corn growers, the nematode situation differs from the Midwest because of different weather, soils and nematode species, says University of Arkansas nematologist Terry Kirkpatrick. In many areas, nematode species and populations are changing, in response to an increase in the amount of corn acreage in recent years.
"In the Southeast, where there is more sandy soil, and more hot, dry weather, nematicides produce a yield response pretty consistently in corn," Kirkpatrick says. "We don’t see as much response in the mid-South, where we have more silt loam soils.
- January 2012