Comparative analysis of the four formulas commonly used for calculating the control efficacy of fungicides on disease in field trials

Field efficacy trials are an indispensable part of pesticide registration management. The applicability, accuracy and effectiveness of the formulas for calculating the control effect of fungicide on plant disease are crucial for the scientific and reasonable evaluation of the field control efficacy of fungicides on plant diseases. At present, the commonly used calculation formulas are different in applicability and calculation errors, but there was no systematic study on the comparison between the commonly used formulas. In this work, four formulas commonly used in field efficacy trials were selected for comparative research. The range of application of the commonly used formulas and the stability of the calculation results were accurately evaluated, and the condition indices observed in the disease index after the treatment were corrected. These results showed that for given disease indexes of the treated groups and the control groups, the four formulas had different sensitivity to the initial difference of disease index between the treated groups and the control groups. When the change of the disease index was extremely small, the results calculated by formula (1), (3) and Yang Xindong's formula (4) were not dependence the disease index of the control groups. When the disease index in the treated groups was reduced after treatment, the results from calculated by formula (1) and (3) were out of the range of corrected efficacy. While Henderson-Tilton formula, namely formula (2) in the paper, was used to calculate the control effect based on the rate of change of the disease index before and after treatment, which could effectively avoid the result deviation or the overflow of the range of corrected efficacy. When the initial disease index was higher in the control groups and disease epidemic occurs rapidly, Yang Xindong's formula was recommended for calculating the control effect, which could reduce errors caused by the difference in disease index after treatment between the treated groups and the control groups. A comprehensive consideration of various influencing factors before and after treatment in field trials indicated that formula (2) was more applicable under the application of fungicides at the early stage of disease development in field.