As Iowa’s corn crop gets slowly planted and established in 2019, it’s time to turn thoughts towards pests. Plant-parasitic nematodes that feed on corn can cause damage and yield loss. Some nematode species are damaging to corn at very low population densities (numbers). But most species are not harmful until population densities reach many hundreds or more per 100 cm³ (a little less than a half-cup) of soil. And then there are some nematode species that are not thought to be harmful to corn at all. It is very common for Iowa fields to have several different species of plant-parasitic nematodes present at low numbers. A summary of results of testing for nematodes that feed on corn in Iowa from 2000 to 2010 is available online.