Root-infecting fungi cause significant damage to soybeans and corn. Fusarium graminearum is a major stalk rot pathogen of corn. Helminthosporiumpedicellatum, a native soil­ borne fungus, causes root rot of corn. Neither of these fungi is controlled well by plant breed­ ing for resistance or crop rotation. Brown stem rot caused by Phialophora gregata is the most important disease of soybean in Iowa. Again, resistance is not completely successful, and rotation of at least four years to another crop is needed to obtain satisfactory control.