Development of plant diseases which can be ruinous to high-value crops such as potato, onions or green beans, depends strongly on temperature and duration of foliage wetness. In potato crops (a $120 -$150 million/year crop in Wisconsin), repeated fungicide sprays are needed to control devastating foliar diseases. In the past, applications were made at regular time intervals (5-7 days).
The prediction of foliar wetness in canopies is so difficult that when plant pathologists developed a potato blight prediction model, they required growers to measure humidity in potato canopies rather than attempt prediction. The inconvienience and expense associated with this humidity measurement discourages growers from participating in the potato blight prediction program.
Foliage wetness can arise from rainfall, irrigation or dew formation. Canopy wetness can be predicted from a model that uses data from grower-measured irrigation and rainfall, GOES-8 satellite radiation estimates, measurements of temperature, humidity and wind speed from weather service locations and agricultural measurement networks, and forecasts from a mesoscale model of the atmosphere.
Our predictions of conditions leading to leaf wetness will be combined by farmers with local information about irrigation and rain, to derive an estimate of how long leaves have been wet. This wetness duration can then be used with existing disease prediction models to determine if a fungicide spray is needed.
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