Methods for maize top rot sampling and its economic loss assessment.

The field survey on occurring rate of maize top rot of 24 varieties(lines) and the evaluation of their resistance with cluster analysis methods were conducted.The results showed that all varieties could be clustered into 5 disease-resistant groups,which was similar to the field survey.The disease occurring rate of diseases which do not cause no harvest(including maize top rat) could not be directly used as the crop loss rate or to calculate the economic loss.It was proper to sample and determine the theoretical yield according to the disease level of crop varieties with different disease resistant levels.The correlation between the theoretical yield and actual yield was not significant by χ2 test and this suggested that the methods for the survey sampling and assessment of crop yield loss were practical.