This plant disease model has been developed by Weather INnovations Consulting LP, called WHEATcast™. The purpose is to provide wheat farmers advice on when to more intensely scout their wheat fields for the presence and severity of septoria tritici leaf spot and powdery mildew foliar diseases.
The model begins on January 1 of the year of harvest, rating each day on a scale of 0-7 based on a proprietary hourly temperature/leaf wetness/relative humidity algorithm where the actual daily disease severity values are accumulated and graphed.
The base site-specific graph identifies two threshold lines. Whenever the actual accumulative disease severity values fall below the yellow threshold line the amount of disease appearing on the wheat foliage is not considered sufficient to cause any loss in yield or seed quality. Whenever the actual location accumulative DSVs rise above the red threshold line, the level of disease has been shown to reduce yields and a fungicide spray application is warranted. It is essential, of course, that the spray application be applied before the accumulative DSVs go much above this line or better still a corrective measure should be considered BEFORE this line is reached. Whenever the actual accumulative DSVs are between these two threshold decision lines it is suggested that the grower needs to inspect the field and determine the degree of infection. A map will be available for a regional assessment of these diseases.
A spray threshold is NOT a fixed value but a decision each grower must make for themselves.