Scouting Onions for Botrytis Leaf Blight Halo Lesions
Christy Hoepting, Extension Vegetable Specialist
Cornell Vegetable Program
Botrytis Leaf Blight (BLB) halo lesions are the tiny pin-prick to pin-head sized yellow necrotic spots surrounded by silvery halos (Fig. 1, lesions 5 and 6). The silvery halo is often blotchy in shape.
Sometimes the necrotic spot is barely visible, which can make identification of such versions of these lesions tricky to identify (Fig. 1, lesions 2 and 3).
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. 1, lesion 9).
Various nicks and dings caused by blowing debris or herbicide injury may be confused with BLB halo lesions (Fig. 2).
BLB halo lesions can be distinguished by their ghostly appearance not penetrating the leaf surface. BLB halo lesions are most abundant on the outer leaves, usually on the underside of the leaf, and are distributed anywhere along the leaf. All of these lesions are counted when scouting to use for spray thresholds for BLB. Count the number of BLB halo lesions on the outer three leaves of 20-30 plants per field. Numbers can be highly variable among plants, so it is good to take a look at several plants. The number of lesions per leaf is the number of lesions per plant divided by 3. The spray threshold is 1.0 BLB halo lesion per leaf.
Scouting Onions for Botrytis Leaf Blight Halo Lesions (pdf; 234KB)
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Upcoming Events
Niagara Region Vegetable Meeting
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August 14, 2024
Clarence Center, NY
We'll start this meeting off at Root Down Farm to hear late season disease management updates in peppers and cole crops, plus current best management practices to limit fungicide resistance. Potato variety recommendations and disease control questions in potatoes will be addressed.
Then we'll head to Kreher's beet field to view and discuss alternative weed control technologies. The beet field is an on-farm demonstration of various flame weeding protocols in comparison with stacked tool cultivation equipment. One or two weeding robots will be on-hand for live demonstrations and discussion of the technology's current abilities and future potential. We'll also cover industry updates and a review of late summer disease management in squash.
2.0 DEC credits will be available in categories 23, 1a, and 10.
2024 Chipping Potato Twilight Meeting
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August 20, 2024
Dansville, NY
Join us for a brief, on-farm meeting including insect pest updates and viewing of the chipping potato variety trial. 1.0 DEC credits in categories 10, 1a, and 23 will be offered. Dinner follows!