Economic effectiveness of resistant varieties and duter/dithane M-45 foliar spray for the control of Philippine corn downy mildew.
All treatments gave a significantly lower percentage infection of maize by Sclerospora philippinensis compared with the controls, but usually the use of resistant cvs. was better than duter/dithane M-45 sprayed on a susceptible cv. No significant differences in infection were obtained between 3 sprays of duter + 5 of dithane M-45 and 2 sprays each of duter and dithane M-45 except during the 1972 dry season at Laguna. Significant increases in yield were obtained in all treatments except 4 and 8 sprays of duter/dithane M-45 during the dry season of 1973. Eight sprays resulted in higher increased income than 4 sprays during the dry season but not during the wet season. The use of resistant cvs. gave the highest additional income.<new para>ADDITIONAL ABSTRACT:<new para>Three maize varieties resistant to Sclerospora philippinensis and one susceptible variety were grown in the field for four years at one site and for one year at a second site, and the effect on yield of spraying with a combination of Duter and Dithane M45 was determined. In most trials the resistant varieties had less infection than the susceptible UPCA1 sprayed with Duter/Dithane M45. When the yields had been corrected to take the varying yield potentials into account, the yield of the resistant varieties did not differ from that of sprayed UPCA1, but the use of resistant varieties was more economical than spraying.