Primary Source of Infection of Curvlaria lunata and Toxicity of some Fungicide to the Fungi

The primary sources of infection of Curvlaria lunata were studied in several methods. The results showed that corn seed is not the primary source of the disease induced by fungi because fungi don′t exist in the interior of and on the surface of corn seed. But fungi in the residue of diseased plant on the surface of soil may become the primary source because they can live through the winter. Fungi in soil, despite the depth where they live, can′t be the primary source due to their short living period. When the isolates of fungi are cultured in PSA medium, its conidia can live though the winter, either on the surface or in soil. This showed that the conidia of fungi may become the primary source. The determination of the toxicity of four fungicides indicated that the most toxic is 50% thiram, with its value of EC 50 being lowest, 11.79 mg/kg. Its toxicity equation is y=3.33+1.56x and the coefficient of correlation is 0.991 2, significantly different at 1%. The other fungicides are sorted out in order as follows: 75% chlorothalonil, with its value of EC 50 being 14.89 mg/kg,its toxicity equation being y=3.78+1.04x and the coefficient of correlation being 0.957 9, significantly different at 1%; 75% zineb, with its value of EC 50 being 36.06 mg/kg, its toxicity equation being y=4.01+0.63x, and the coefficient of correlation being 0.955 5, significantly different at 1%; 75% mancozeb, with its value of EC 50 being 64.95 mg/kg, its toxicity equation being y=2.08+1.61x, and the coefficient of correlation being 0.967 0, significantly different at 1%.