Spread of Corn Anthracnose from Surface Residues in Continuous Corn and Corn-Soybean Rotation Plots

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Abstract
The development of anthracnose [Colletotrichum graminicola] leaf blight was monitored at 14-day intervals to determine disease spread from corn residues on the soil surface in plots maintained under continuous corn or a corn-soybean rotation during 1984 and 1986. The number of infected leaves per plant was negatively correlated (P < 0.01) with distance from the residue area in both plots from 28 to 70 days after planting. No net increase in the number of infected leaves per plant was detected after this period (70-112 days). Among-group regression analysis indicated a significant difference (P < 0.01) between within-row and across-row spread of leaf blight in the corn-soybean rotation and the continuous-corn plots. The difference in slopes of the regression lines indicated that leaf blight spread more rapidly within rows than across rows. The percentage of plants with anthracnose stalk rot at the end of the season was negatively correlated (P < 0.01) with distance from the residue area in both plots in 1984, but only the corn-soybean rotation plot in 1986. Stalk rot incidence was higher in the continuous-corn plots than in the corn-soybean rotation plots, and incidence was higher at greater distances from the residue area. Results indicate that surface corn residues are an important source of inoculum for anthracnose and the rate of disease spread may depend on the orientation of corn rows in relation to the inoculum source and cropping history of the field.