Know the Difference: Botrytis Leaf Blight Halo Lesions vs BLB Necrotic Spots
Christy Hoepting, Extension Vegetable Specialist
Cornell Vegetable Program
Through recent on-farm fungicide trials, we've determined that not all Botrytis leaf blight (BLB) lesions are controlled equally. There are two kinds of BLB lesions: BLB halo lesions and BLB necrotic spots and your best fungicide options for control of Botrytis leaf blight depends on what kind of spot you got! See Know the Difference: Botrytis Leaf Blight Halo Lesions vs BLB Necrotic Spots for photos.
BLB Halo LesionsWhen BLB first occurs in June and early July, the lesions appear as a tiny yellow necrotic spot surrounded by a silvery halo. It is also common for the necrotic spot to be absent leaving just a silvery spot (Fig. 1). When BLB halo lesions get old, the center becomes sunken and often splits; it is still yellowish in color and remnants of the silvery halo can usually still be seen (Fig. 2).
See Scouting Onions for Botrytis Leaf Blight Halo Lesions for more more information and photos.
During the second half of July, BLB lesions often do not have the silvery halo. Instead, they are yellow spots, sometimes yellowish-white spots as they get bigger, with a round defined border, that are pin-prick to 1 mm or slightly larger in size (= BLB necrotic spots) (Fig. 1 and Fig. 3). By August, BLB necrotic spots are often dominant, while BLB halo lesions decline, especially in Elba muck. BLB halo lesions tend to linger for the duration of the season in Wayne and Oswego muck-onion growing regions, although both do occur.
BLB necrotic spots are not to be confused with old BLB halo lesions where the initial necrotic spot becomes sunken and often split (Fig. 2). BLB necrotic spots could also be confused with contact herbicide injury.
Know the Difference: Botrytis Leaf Blight Halo Lesions vs BLB Necrotic Spots (pdf; 264KB)
Asparagus
Beets
Broccoli
Brussels Sprouts
Cabbage
Carrots
Cauliflower
Cucumbers
Dry Beans
Eggplant
Ethnic Vegetables
Garlic
Horseradish
Kohlrabi
Leeks
Lettuce / Leafy Greens
Melons
Mushrooms
Onions
Parsnips
Peas
Peppers
Potatoes
Pumpkins / Gourds
Radishes
Rhubarb
Rutabaga
Snap Beans
Squash - Summer
Squash- Winter
Sweet Corn
Sweet Potatoes
Tomatoes
Turnips
Upcoming Events
2026 NYS Processing Vegetable Educational Meeting
March 16, 2026
Batavia, NY
Processing vegetable industry members who grow, manage, or support crop production for Farm Fresh First/Nortera Foods, Seneca Foods and/or Love Beets, are encouraged to sign-up for the 2026 NYS Processing Vegetable Industry Meeting! You will:
- Network at this in-person meeting.
- Learn the results of industry-funded research.
- Have a voice in Cornell research and Extension.
DEC recertification credits available: 2.0 in categories 1a, 10, and 23.
2.0 Certified Crop Advisor (CCA) credits available.
Virtual Asparagus School
March 17, 2026
Join us to dive deep on growing asparagus! Bringing together experts from the Cornell Vegetable Program, Michigan State University, OMAFA (Ontario Ministry of Agriculture, Food, and Agribusiness), and industry, featuring a panel of growers.
Postharvest Water Management, Sanitation, and Traceability Workshop
March 18, 2026
Albion, NY
Cornell University personnel from the National GAPs Program and the Produce Safety Alliance are presenting a workshop on postharvest water management, sanitation, and traceability. This workshop will include a mix of short talks and hands-on activities to provide attendees with applied experience with sanitation, postharvest water, and traceability topics.
2.75 NYSDEC CEU's in categories 10, 1a, and 23 available.