Studies on Damage Caused by Spring Maize Curvalaria Leaf Spot and its Economic Threshold in Liaoning Province

[Objective] The propose was to study on the damage caused by spring maize Curvalaria leaf spot and its economic threshold in Liaoning Province from the view of disease level and disease index of maize Curvalaria leaf spot.[Method] With maize variety Shendan 16 as the tested material,5 gradients(5.0×104,1.0×105,2.5×105,5.0×105,1.0×106 spores/ml)were set up for artificial inoculation of maize Curvularia leaf spot fungi and the CK treatment was also set up in the field test with the completely randomized block design.After the fungi were inoculated for 7 d,the investigation on the disease level number was conducted and their disease severity was divide into 6 levels according to the national standard.[Result] With the increase of maize Curvularia disease levels,the grain number,grain weight,yield showed the decreasing trend.The maize Curvularia leaf spot disease level and disease index had a very significant positive correlation with the loss rates of the grains of ear,weight of hundred grains and the yield.If the disease-level was taken as the economic threshold level of controlling maize Curvularia leaf spot,the disease-level was average of 0.45;if the disease index was taken as the controlling index,the disease index was 14.10.[Conclusion] The study provided the reference basis for the scientific establishment of economic thresholds for controlling Curvularia leaf spot of spring maize in Liaoning.