No Late Blight Reported Yet - But Growers Should Stay Alert

By Blake Jackson

No cases of late blight have been reported in the United States as of August 11, 2026, according to Penn State Extension monitoring efforts. Growers are still encouraged to remain vigilant because the disease can spread rapidly and cause serious losses in potato and tomato crops once established.

Late blight is caused by Phytophthora infestans, a fungal-like organism known as an oomycete. The disease primarily affects potatoes, tomatoes, and certain weeds in the nightshade family.

Pennsylvania's cold winters generally prevent the pathogen from surviving outdoors, although it may persist in warm compost piles if living plant material is present.

The pathogen can also enter the state through infected potato seed, transplants, or airborne spores carried from other regions.

Symptoms can appear on leaves, stems, and fruit. Early signs include pale green, water-soaked, or brown leaf spots that expand quickly. During humid conditions, white fuzzy growth may develop on the undersides of leaves near infected areas.

Stem and petiole infections often cause rapid collapse of foliage above the lesion, and severe outbreaks can result in extensive defoliation within two weeks.

Penn State Extension recommends an integrated management strategy to reduce risk. Using certified seed, healthy transplants, and resistant varieties helps prevent disease introduction and establishment. Regular field scouting and monitoring regional disease reports are also important for early detection.

Fungicides provide the greatest protection when applied before infection occurs or immediately after symptoms are detected. Weather-based forecasting tools can help improve application timing and effectiveness.

Additional cultural practices, including improving air circulation, controlling weeds and volunteer host plants, and removing infected plant material, can help slow disease spread.

For organic growers, preventive programs are especially important because copper-based products remain the primary option for disease suppression.

Growers should consult the 2026-27 Mid-Atlantic Commercial Vegetable Production Recommendations for the latest crop-specific fungicide and management recommendations.

Photo Credit: gettyimages-bastetamn