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 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.
Remote Good Agricultural Practices (GAPs) Training
February 12, 2025
Join Cornell Cooperative Extension of Orange and Oneida Counties, the Cornell Vegetable Program, Harvest NY, and the Eastern NY Horticulture Team on Feb. 12 for a remote Good Agricultural Practices (GAPs) training. Good Agricultural Practices is a voluntary food safety audit program requiring minimum standards for the production, handling, packing, and storing of fresh fruits and vegetables, and is required by some buyers. Trainers will cover food safety best management practices related to worker training, preharvest assessments and wildlife management, water testing, postharvest handling, hygienic equipment design and efficient wash-pack setups, how to write a farm food safety plan, and more. The training will follow the USDA GAPs audit checklist so that farms will be prepared for an audit. A NYSDAM GAPs auditor will join us to discuss audit logistics and answer questions from participants. Following the course, we will offer a series of virtual office hours to follow up with course participants to assist them with writing their farm food safety plan, which is mandatory for the GAPs audit. Participants will receive a certificate of course completion after the training.
Food Safety Lunch and Learn Webinar Series
February 11, 2025 : Part One: What's Going on with Food Safety?
NYS Department of Agriculture and Markets FSMA inspectors are expected to step up farm visits this season. Why are they showing up on the farm asking about FSMA? Aren't we exempt? This noontime hour we will discuss the purpose of the farm visits and what produce farmers need to know.
February 18, 2025 : Part Two: What Counts as Food Processing?
In this session, we will discuss what counts as processing and what doesn't. Stories of inspectors coming to farmers markets and auctions telling some growers certain products can't be sold usually without much explanation. We will try to make some sense of things and clear up some misunderstandings so hopefully the upcoming season goes smoothly.
February 25, 2025 : Part Three: Traceability - Benefits for Food Safety and Beyond
Can having a traceback process for your produce (and other farm products) make good business sense regardless of FSMA regulations? We will (try to) make the case for farms to have some sort of traceability mechanism in place.