2026 Late Blight Updates

Week of September 22

New late blight infections continue to be confirmed across the Mid-Atlantic. New York, Vermont, and Canada have all reported infections this month. The risk of infection is high for Pennsylvania tomato growers especially in the northwest corner of the state. Tomato growers in northwest PA who desire to harvest in the fall, even tunnel and greenhouse growers, should not slack in applying protectant fungicides now. Field growers who have a strong crop and market should use an effective late blight fungicide such as Revus Top, Orondis Opti, Orondis Ultra, Ranman, or Presidio. These products have PHIs varying from 0-2 days, so be sure to check the label before you spray. Over the course of the season, successful spray programs include two or three targeted fungicides alternated with chlorothalonil or mancozeb.  

Late blight has been confirmed in at least four western New York counties: Genessee, Livingston, Onondaga, and Chataqua. Of particular interest to Pennsylvania growers is the case in Chataqua County which borders Pennsylvania (see map below). 

Late blight symptoms can develop on leaves, stems, branches, and both green and ripe fruit. On leaves, pale green to brown spots appear on the upper surfaces. Leaf spot margins are often pale green or water-soaked. The spots may enlarge rapidly until entire leaflets are killed. In moist conditions, a fuzzy white sporulation usually develops near the margins of leaf spots on the undersides of leaves. When late blight infects petioles and stems, all foliage above the lesions rapidly becomes blighted and collapses. Lesions can expand rapidly, resulting in extensive, if not complete, defoliation within 14 days.

Read Late Blight in the Home Garden to see photos and learn more about late blight disease cycle and development. 

Late Blight Management

Fungicides are most effective when applied preventively or at first symptom detection. Weather-based models can further optimize application timing. Cultural practices—such as improving air circulation, managing weeds and volunteer hosts, and removing infected plants—help limit disease spread, which can devastate fields within days under favorable conditions.

Organic systems rely primarily on protectant products such as copper, making proactive management essential. Refer to the 2026-27 Mid-Atlantic Commercial Vegetable Production Recommendations for a complete list of crop-specific fungicide recommendations.

If you suspect late blight in your tomato or potato field, please contact your local Extension office or send a plant sample to the Penn State Plant Disease Clinic. Since late blight can move quickly, prompt identification and reporting is crucial to allow growers to respond before the disease spreads.