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 cor n (Zea mays) by host resistance or fungicides. Different levels of par tial rust resistance in sweet corn hybrids and levels of fungicidal co ntrol were compared in field trials from 1987 to 1992. The level of co ntrol provided by partial resistance depended, in part, on the effecti veness of fungicides. In the absence of fungicidal control, rust sever ity on the resistant, moderately resistant, and moderately susceptible hybrids was 15, 40, and 60%, respectively, of the amount of rust on t he susceptible hybrid. When fungicide applications reduced rust severi ty on the susceptible hybrid by half, severity on the resistant, moder ately resistant, and moderately susceptible hybrids was about 20, 55, and 80% of that on the susceptible hybrid. Thus, there was an interact ion between fungicidal control and partial resistance. These relations hips and previously derived yield loss models are used in a hypothetic al example which compares the value of various methods of control.