The development of a risk assessment method to identify wheat crops at risk from eyespot

Abstract

The aim of the project was to develop a risk algorithm allowing growers to accurately determine the need for eyespot treatment in their wheat crop. Over three seasons, commercial crops and detailed fungicide trials were evaluated to test the influence of agronomic factors on eyespot development and to judge the cost effectiveness  of treatment. Many factors affected disease outcome. Soil type, sowing date, previous crop, presence of eyespot at stem extension, spring rainfall and tillage were identified as being significant influences, independent of other factors. For development of the risk algorithm, an additive measure of risk was adopted to form a single explanatory variable, incorporating elements of the individual risk factors identified as useful predictors of the probability of eyespot, scaled according to their contribution to overall risk. To facilitate calculation by users, these values were scaled as follows:

The maximum risk score a crop could be assigned was 50. Two treatment thresholds were set, a risk-sensitive threshold and a risk-tolerant threshold. The risk-sensitive threshold treatment was set at 20 points, predicting a final disease incidence of 30%. Using the risk-tolerant threshold, treatment would not be triggered until 29 risk points were accumulated which would predict a final disease incidence of 45%. This approach allows flexibility on the part of the user in determining what level of risk is acceptable to them.

This is the final report of a 43-month project that started in August 2001. The work was funded by a contract of £241,055 from HGCA (project no. 2382).