CONTROL OF TAR SPOT OF MAIZE AND ITS EFFECT ON YIELD

The tar spot disease complex of maize and the effects of fungicides on disease development were examined during the November-April 1988 crop ping season in Mexico. The disease is caused by two fungi, Phyllachora maydis Maublanc and Microdochium maydis Muller & Samuels (teleomorph = Monographella maydis Muller & Samuels). The ascostromata of P. maydi s can be observed on the lower leaves of the plants generally 10-18 da ys before silking. M. maydis, the second fungus involved in the comple x, was found in infected tissues 10-14 days after ascostromata formati on. Lesions subsequently enlarged, appeared water-soaked, and coalesce d to cause leaf blight. Application of the fungicides Captan, Fenpropi morph, Carbendazim, Mancozeb, and Propiconazole significantly reduced the area under the tar spot disease progress curves, which in turn sig nificantly increased grain yields. Fenpropimorph resulted in the lowes t overall disease severity but not the highest yield. Disease severity in plants sprayed with Mancozeb was not significantly different from that in plants sprayed once with Fenpropimorph, but the former treatme nt resulted in higher yields and a lower incidence of Fusarium stalk r ot.