There continues to be lots of questions about whether plant-parasitic nematodes are causing damage to Iowa’s corn crop. This varied group of microscopic worms has some species that cause damage to corn at very low population densities (numbers) and other species that are not harmful until population densities reach many hundred or more per 100 cm3 (a little less than a half cup) of soil.

It is common for several different species of plant-parasitic nematodes to occur in Iowa cornfields at low numbers. But if numbers increase to damaging population densities, symptoms of injury will appear.

What are symptoms of nematode damage to corn?

Nematode damage symptoms on corn include stunting of plants, yellowing of leaves and mid-day wilting or leaf curling. Roots may be stunted, fine roots may be lacking and there may be discrete areas of black, dead tissue – called lesions – on the roots. Also, some nematodes cause roots to swell.

When do symptoms of nematode damage appear during the season?

It would be very unusual for symptoms of nematode damage on corn to occur in the first month of the growing season - except in fields with very sandy soil. For fields with medium and fine textured soils, the aboveground symptoms caused by nematode feeding likely will appear more in the middle of the growing season.