Digging the plants carefully at this time can reveal the swellings on the roots called galls or knots that form around the developing female root knot nematode. Little can be done after galling is seen. Frequent irrigation can help minimize the damage to the infected root systems. Check for root knot by soil sampling fields to be planted to susceptible vegetables in the fall before planting the crop. Picture taken from Disease and Pests of Muskmelons and Watermelons, Richard Latin, Extension Specialist Plant Pathology, Purdue Univeristy Cooperative Extension Service, West Lafayette, IN, BP-44 Sweet corn.
Common rust is present in some plantings of susceptible sweet corn.
If rust is seen before whorl stage, fungicide control may be beneficial. Scouting young sweet corn for rust is highly recommended. If Pythium is the only concern apply Ridomil Gold EC in a 7-in. For early blight susceptible varieties the high rate of a protectant fungicide is recommended. Disease pressure from foliar diseases is very low at the present time.