Date of Award


Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)


Plant, Soil, and Environmental Sciences


Gregory Porter

Second Committee Member

David Lambert

Third Committee Member

George Criner


When left unchecked and under the right conditions, late blight can destroy a crop of potatoes in days. Fungicides remain the easiest and most important method of control for late blight, but fungicide costs can be significant when weather conditions favor late blight. Reducing the amount of fungicide used would help improve farmer profits. Research in other regions has shown that late blight resistant potato varieties (LBRV) do not need as much fungicide as is currently recommended for susceptible varieties and can provide greater protection against crop loss in the event of an epidemic.

LBRV potatoes from the University of Maine breeding program were tested in two fungicide schedules during the 2011 and 2012 growing seasons. A schedule based on UMaine Extension recommendations was the standard program and a reduced schedule that skipped every other weekly application was compared to the standard program. Two late blight resistant breeding program clones were grown under these management programs and compared to susceptible and resistant checks (Katahdin and Defender, respectively).

Foliar late blight was not observed in the research plots during 2012. In 2011, late blight was observed and there was no significant difference in foliar late blight incidence in the new LBRV potatoes compared to Defender. Katahdin had a much higher severity of foliar disease than the resistant varieties and foliar disease severity of Katahdin was much higher in the reduced schedule than in the full schedule. Fungicide program had no effect on total yield or marketable yield in any of the growing seasons and surprisingly did not even affect yield of Katahdin during 2011 under heavy disease pressure. Storage rot incidence was not consistently affected by the fungicide program; however there was a trend toward greater rot incidence in the reduced fungicide program. The potential for increased storage losses under this type of management program will need further investigation. The reduced fungicide programs provide substantial savings in the amount of fungicide used and also would reduce fuel, maintenance, and labor costs. Per acre savings were calculated as part of this project.

Profits could likely be increased with the implementation of LBRV potatoes and reduced fungicide spray programs, but uncertainty remains. Date of disease introduction, unusual weather patterns, and the unreliability of the storage rot data limit the immediate application of these findings; however, they provide a basis for continued exploration of the potential use of LBRV to reduce grower costs and the risk of losses from late blight. A model based on long-term weather data and the severity of late blight outbreaks in Aroostook County was developed as part of this project and may provide clearer insight as to when reduced schedules are appropriate, as well as their potential benefits.