Late blight confirmed on tomato in Northumberland Co., PA

Posted: August 19, 2011

On Aug 17, 2011 late blight was confirmed in a commercial tomato field in Northumberland Co., PA. Foliar symptoms were observed in one small corner of the field following extensive scouting.
Late blight sporulation on the underside of a tomato leaf (Photo: Sara May).

Late blight sporulation on the underside of a tomato leaf (Photo: Sara May).

Late blight specific products were being used as part of the fungicide program. It is thought that the sprayer boom missed this corner of the field when turning around. A sample was submitted to Bill Fry at Cornell for genotyping. Additionally, late blight was confirmed earlier this week on tomato in a home garden in Washington Co., RI.

The other report of late blight in PA was in a commercial potato field in Cambria Co., PA in mid-July. Heavily sporulating foliar and stem symptoms were observed. It was identified as US23, the same genotype as the outbreaks reported on Long Island in early July. US23 is sensitive to mefenoxam, the active ingredient in Ridomil, and it is a pathogen of both potato and tomato.

As the evenings become cooler (64 to 71°F) with longer dew periods, the conditions are becoming more favorable for late blight. Vigilant scouting for late blight is still important!

Remember that late blight is a community disease! If you suspect late blight please contact your local Penn State Cooperative Extension Office, the Penn State Plant Disease Clinic or Beth Gugino at or 814-865-7328. For the most current map of confirmed late blight outbreaks please visit