By Greg Tylka, Department of Plant Pathology and Microbiology
Most Iowa cornfields harbor one or more species of these
microscopic, plant-parasitic worms. At least 28 nematode species
have been found associated with corn in Iowa. Most are not
thought to cause damage at low population densities (numbers).
The estimated damage threshold for most nematodes that feed on
corn in Iowa ranges from 100 to 1,000 worms per half-cup (100
cc) of soil (see August 2009 ICM News article). Only dagger,
needle and sting nematodes are considered damaging at low
numbers. The results of Iowa State University testing, from 2000
to 2010, for nematodes that feed on corn in the state were
summarized in a recent ICM News article. Sample timing is key
Knowing the types and numbers of nematodes present in a field is
useful in gauging the possible benefits of nematode-protectant
seed treatments or soil-applied nematicides. Unfortunately, most
nematode numbers will be low in spring soil samples, even though
they can develop to higher, da