Studies on Spatial Distribution of Northern Leaf Blight and Gray Leaf Spot of Maize in Changchun Region

The spatial distribution of northern leaf blight and gray leaf spot of maize in Changchun region. The results showed that spatial distribution pattern of northern leaf blight of maize was random at the beginning of the disease developing, and evenness at the last stage. Spatial distribution pattern of gray leaf spot of maize was aggregation. The optimum sampling number of the two diseases were determined under different density according to the optimal sampling formula was built up as n=t2/D2×[(α+1)/-X+β-1].