Do you have a corn nematode problem? Is your nematicide doing any good?
According to Plant Diagnostic Clinic and IPM coordinator Suzanne Bissonnette, unexplained yield losses or patchy areas of low productivity or vigor may indicate not a herbicide, nutrient, or environment issue but an established corn nematode population. A 2009-2010 survey supported by the U of I National Institute of Food and Agriculture-Extension Illinois Pest Management program showed that corn nematode populations were a bigger issue than had been previously thought.
Corn nematodes include a number of damaging species, such as dagger, lance, lesion, ring, stunt, and occasionally, spiral nematode, which may be found in heavy soils.
“Different nematode situations require different types of product application, so it is best that you send in a sample for analysis before attempting nematode control,” said Bissonnette. “You have no other way of knowing what your initial population is or if the population is being controlled.”
The survey found that about half of the cornfields in Illinois have lesion nematode populations with densities at or above the threshold for moderate to severe risk of injury (yield loss). Lesion nematodes are not only capable of injuring corn roots, but they also frequently act as vectors for the development of root rots.
It is not true that corn nematodes are a problem only in very sandy soils. Sandy soil is a risk factor for only a few species (needle, sting, and stubby-root nematodes throughout Illinois, and southern root-knot nematode in southern Illinois). Although needle nematode can kill corn seedlings, most nematodes will not cause severe injury unless the infestation level is very high.
Bissonnette said, “Consider sampling for nematodes now, especially in corn fields that are at risk.” Some risk factors include corn-on-corn growing, minimal or no tillage, and the absence of nematode-suppressing soil-applied insecticides. The best time to sample for nematode diagnosis is approximately 4 to 6 weeks after planting. The pest management strategy depends on the species involved and how high their numbers are, so it is very important to get a good sample.
Start by examining the physical characteristics of the plants: If there are no symptoms (hot spots) in the field, sample a representative area of the field, perhaps 10 acres or less. Sample in a zigzag or “w”-shaped pattern, and collect 20 to 25 cores in a bucket. If there are hot spots, sample around their edges, not in the centers, and collect a total of 20 to 25 cores. Record the GPS coordinates for the area.