As yet, there still are more questions than answers on nematodes and what they do. Once thought to be mainly a warm-climate problem, some nematodes now are known to be active in northern parts of the state.
Norton, Dan C. and Worf, Gayle
"We're Learning For About - Nematodes: Hidden Plant Destroyers,"
Iowa Farm Science: Vol. 17
, Article 4.
Available at: https://lib.dr.iastate.edu/farmscience/vol17/iss1/4