4.9.1
LATE BLIGHT PREDICTION AT THE GROWER LEVEL

S JOHNSON

University of Maine, Presque Island, USA

Background and objectives
Potato late blight, caused by Phytophthora infestans, is one of the most destructive foliar diseases on potatoes and has been around for over 150 years. Most potato-growing areas have developed prediction schemes to schedule fungicide application to control this pathogen. The traditional approach of centralized late blight prediction from remote weather stations removes the grower from the process. Involving growers in the prediction process provides information on the basis of which more knowledgeable decisions can be made. The purpose of this effort was not to take the advisors out of late blight prediction, but to put late blight prediction into the hands of the users. Growers and advisors have roles that need to be filled.

Personal computers can easily handle the data analyses required for late blight prediction. Good quality automated weather stations are available and reasonably priced. Automated weather stations connected to grower-owned and -operated computers can do a credible job of weather data collection. The final need is for computer software to analyse the weather data collected for late blight prediction. The computer program NoBlight was developed specifically for this purpose. Severity values [1] and spray interval recommendations are determined using current on-site weather data.

The initial network consisted of seven weather stations covering 25,000 ha of potatoes grown on nearly 475 farms. The weather stations and the late bight prediction software were on site and operated by the growers. Twice weekly during the growing season, information was electronically sent to a central location. The information was interpreted and put onto a Late Blight Hotline. This was a voice-mail system operating on a toll-free telephone line available on a 24-hour basis.

Results and conclusions
The backbone of the Late Blight Hotline system is the automated weather stations and the NoBlight computer program operated on grower sites. After brief initial training, the growers with the weather stations and NoBlight on their computers were able to handle the weather data downloading, late blight prediction and internet transfer of data to a central location with a minimum of assistance. The growers operating the weather stations and NoBlight developed improved decision-making skills with respect to late blight control. An average of three applications of late blight protectant were saved on each site. The number of weather stations in the system will double in the coming year, these being purchased by interested growers. The Late Blight Hotline received more than 14 calls per day and over 40 calls per day at the peak of the growing season. This was widely popular and has been requested for the coming season.

The interpretation of the weather data and the skill of the forecaster are still critical factors in late blight prediction. With practice, growers can interpret weather data and become better forecasters. The more information available to the grower, the better the decision becomes. A decentralized weather network and late blight prediction network actively involves the producers in their own decisions. On-site late blight prediction by the growers is proving a successful approach and is increasing in Maine.

References
1. Krause RA, Massie LB, Hyre RA, 1975. Plant Disease Reporter 59, 95-98.