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Scouting Onions for Botrytis Leaf Blight Halo Lesions

Christy Hoepting, Extension Vegetable Specialist
Cornell Vegetable Program

May 21, 2024

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. 



BLB Lesions on an onion leaf

Figure 1. Ten Botrytis leaf blight (BLB) halo lesions on an onion leaf. Lesion No. 1, 4, 5, 6 and 7 have tiny yellow necrotic centers. In lesion No. 2, 3 and 10, the necrotic center is not visible. Lesion No. 8 does not have a distinct yellow center and blends into No. 7. Lesion No. 9 is an old lesion with a sunken center and silvery halo still visible. Photo: C. Hoepting, CCE Cornell Vegetable Program









BLB lesion among other nicksFigure 2. BLB halo lesion amongst other necrotic spots on onion leaf. Photo: C. Hoepting, CCE Cornell Vegetable Program


Scouting Onions for Botrytis Leaf Blight Halo Lesions (pdf; 234KB)

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Upcoming Events

2025 Finger Lakes Auction Winter Growers Meeting

Event Offers DEC Credits

January 2, 2025
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At this grower-focused meeting, ag industry experts will discuss pest control in vegetables, weed management strategies and best practices, seed germination, an introduction to foliar nutrient uptake in vegetables, and grouping flowers by growth needs. Plus we'll hear from a grower panel from Kutztown Produce Auction, moderated with NYS specific pest control from Judson Reid.

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Announcements

Laser Scarecrows to Deter Birds in Sweet Corn

Are you considering the use of a laser scarecrow to deter birds on your farm? Cornell Cooperative Extension and the University of Rhode Island teamed up to test a research laser scarecrow on sweet corn farms.

A laser scarecrow is a device that has one or more laser modules connected to motors. The specifications of the lasers are optimized to the color and motion sensitivity of bird's eyes. When laser beams move across a field, birds become frightened and attempt to move away from the perceived threat. Light from the laser covers an area quickly and moves through the canopy without causing injury to the crop. Research demonstrates that birds do not readily become habituated to the laser.

A laser scarecrow used as the sole deterrent typically results in a significant reduction in crop damage. Combined with an auditory device, damage can be reduced even more. When used as part of an integrated management program for bird control that utilizes habitat management and multiple scare tactics, laser scarecrows can be useful tools for growers of multiple crops. All scare tactics must be deployed before birds find the field. The effectiveness of lasers depends on multiple factors such as bird species, bird populations, habitat and food availability. Lasers are not effective at deterring deer, racoons, coyotes or other mammals.

To learn more, the Laser Scarecrows to Deter Birds in Sweet Corn and Other High-Value Agricultural Crops fact sheet provides background information, research data, FAQs, and Advantages/Limitations on laser scarecrows.

NY Urban Farms Pest Management Fact Sheet Series

Cornell Cooperative Extension has partnered with dozens of urban farms across New York State to demonstrate and evaluate sustainable pest management strategies. Together with farmers, we found success using control methods that prevent or reduce crop losses through exclusion strategies, crop timing, host resistance, the introduction of beneficial organisms, and more. Regardless of management strategy used, common requirements for success include a knowledge of the pest and disease complex, preventative deployment and commitment to the process. The New York Urban Farms Sustainable Pest Management Fact Sheet Series includes case studies highlighting pest management techniques that New York urban farms have found valuable.

NYS Urban Growers Pest Management Needs Assessment

As part of a multi-year project exploring non-spray pest management options that are economically and environmentally sustainable for urban farms, we conducted a needs assessment with urban growers across New York State. The New York State Urban Growers Pest Management Needs Assessment presents findings on current pest management practices, challenges, and topics of future interest.

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