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)
Upcoming Events
2025 Ontario Produce Auction Winter Growers Meeting
January 15, 2025
Stanley, NY
This grower-focused meeting will include information about pesticide applicator recertification and record keeping requirements, disease control in cole crops and vine crops, and using biocontrols for insect management in greenhouses. Several seed and ag input companies will be on-hand to share product news.
2.75 DEC recertification credits will be offered in categories 10, 1a, 23 and 24. CORE credits (0.5) offered too!
2025 New York State Potato School
February 11 - February 12, 2025
Waterloo, NY
This year's program will feature speakers covering critically important topics like disease management, updates in storage techniques, new varieties, and other production management practices. New for this year will be the Processor Panel where guests will have the chance to interact with some of the major chip processors in the northeast. Your participation will also earn you DEC and CCA points.
Intro to Food Safety and GAPs Training
February 19, 2025
via Zoom,
This virtual workshop will serve two purposes:
- For produce farms just interested in learning about farm food safety, this program will introduce principles and best practices.
- For produce farms look for a GAPs (Good Agricultural Practices) training needed to meet buyer demands for audit/certification, this program will provide that as well.