Nematodes Nip Corn Yields Now

May 26, 2010 09:17 AM
Corn nematodes are microscopic creatures that can take a chunk out of your corn yield potential and, in the process, escape detection.
Photo by Greg Tylka,
Iowa State University Extension
That's because nematode damage looks similar to damage caused by other issues such as nutrient deficiencies, insect feeding, herbicide injury, disease or compaction, according to Missy Bauer, Farm Journal Associate Field Agronomist.
The timing for nematode damage is similar, too.
"Roughly four to six weeks after planting is when you can first notice a problem,” she says.
Bauer recommends that farmers scout their fields for circular patches of corn plants that are yellowing or stunted.  If nematodes are the culprit, the damage typically is most severe in the center of the circle and then becomes less noticeable around the outside edges.
"Sometimes you'll find ‘hot' spots distributed around your field, too, which simply reflects where the nematodes are present,” she adds.
Yield reductions of less than 10 bu./acre are common, though losses can be extreme.
The needle nematode, which is most easily identified this time of year in corn roots, can cause losses of up to 62%, according to University of Illinois Extension research.
The good news is this parasite is found primarily in only those soils with 70% or more sand content.
The bad news is that there are more than 60 different species of nematodes, of which 12 or so are most damaging to corn, and one or more of these species is present in every soil type across the Corn Belt.
Researchers believe nematode damage is on the upswing due to three factors: increased corn-on-corn acreage, reduced tillage and the use of new pyrethroid insecticides that do not protect against nematodes.
Now is the time to begin checking for nematodes, Extension researchers say.
"Obtaining a good sample is the basis for a reliable diagnosis,” states Terry Niblack, University of Illinois Extension nematologist, in a recent university-distributed news release. "If there are no visible plant symptoms, sample a representative area of a field, perhaps 10 acres in size. Walk a zigzag or W-shaped pattern, and collect 20 to 25 soil cores in a bucket. A one-inch soil probe is the preferred tool to use. Sample as deep as possible, typically 12 inches, from within the rows. The soil should be moist but not wet.
"Treat the soil samples gently, as some nematode species are very sensitive to manipulation. Soil cores should not be dropped or crumbled. Place the soil samples in a plastic bag. Keep the samples cool (place in a refrigerator or cooler) until being mailed or delivered to the laboratory.”
If nematodes are present in your field, there is, unfortunately, little you can do this year to control them, but you can plan ahead for next year.
Avicta Complete Corn, introduced by Syngenta in 2009, is a seed treatment fungicide that offers protection against nematodes during germination and stand establishment.
Bayer CropScience Poncho/Votivo biological seed treatment received EPA approval for farmer use this spring. Bayer representatives say the product protects corn plant roots so nematodes have limited to no ability to feed.
Bauer is evaluating both products in field trials this season. In addition, she is pulling 350 corn nematode samples across 20 Michigan counties. The samples will be analyzed for various nematode species, including: lesion, root knot, lance, needle, spiral, stubby root, stunt, ring and dagger. This research is being funded by a grant provided by the Corn Marketing Program of Michigan. Farm Journal will report on Bauer's research through the growing season and also postharvest.

Learn more about nematode pressures, identification, diagnostics, and ongoing Farm Journal Test Plots research at this summer's Corn College. One-day sessions are still open for registration.



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