COMPARING PARTIAL RESISTANCE TO PUCCINIA-SORGHI AND APPLICATIONS OF FUNGICIDES FOR CONTROLLING COMMON RUST ON SWEET CORN

Common rust, caused by Puccinia sorghi, can be controlled on sweet corn (Zea mays) by host resistance or fungicides. Different levels of partial rust resistance in sweet corn hybrids and levels of fungicidal control were compared in field trials from 1987 to 1992. The level of control provided by partial resistance depended, in part, on the effectiveness of fungicides. In the absence of fungicidal control, rust severity on the resistant, moderately resistant, and moderately susceptible hybrids was 15, 40, and 60%, respectively, of the amount of rust on the susceptible hybrid. When fungicide applications reduced rust severity on the susceptible hybrid by half, severity on the resistant, moderately resistant, and moderately susceptible hybrids was about 20, 55, and 80% of that on the susceptible hybrid. Thus, there was an interaction between fungicidal control and partial resistance. These relationships and previously derived yield loss models are used in a hypothetical example which compares the value of various methods of control.