(July 2013) Late blight (LB) in potatoes and tomatoes has been confirmed in a commercial field and a garden in Erie County, and in a commercial field in Madison County. (Both of the Erie County samples were just identified as US-23.)
In all cases wet soils prevented a fungicide application for nearly three weeks. For the most current info on LB confirmations go to: usablight.org.
Many growers in and around the CVP counties have had stretched spray intervals due to the repeated, heavy rainfall. Forecast systems have recommended a 5 day fungicide spray interval for several weeks (for most fungicides).
Late blight is expected to pop up in many more fields and gardens over the next weeks. Immediate action is needed to limit spread and losses. In cloudy weather LB spores can move on winds and cause infection up to 30 miles away.
Scout your fields carefully! Especially check fields where spray schedules have been stretched, near tree lines, in/around wet spots, in small, protected fields. Inspect lower leaves and stems, also new growth since the last spray, and everything in between, including tomato fruit. Check sprouts in potato cull piles, compost piles, volunteers, and then kill any sprouts found immediately.
From Abby Seaman, NYS IPM Vegetable Coordinator:
How to scout for LB, view a video at: https://www.youtube.com/watch?v=3DuCzIFVfyNow
Photos of LB on potato or tomato, and LB imitators, are at Cornell plant pathologist Meg McGrath’s photo index at: http://www.longislandhort.cornell.edu/vegpath/photos/index.htm. Click on Tomato or Potato, then Late Blight.
Late Blight brochures for gardeners – For the rest of New York are available from the tomato or potato LB pages, at the top right. Click on it to print a leaflet with color photos and recommendations to give to your neighbors or customers.
If LB is detected or suspected contact us ASAP for positive identification and for determination of the LB strain by Bill Fry’s lab, Cornell. Collect at least five leaves/stems with fungal lesions on otherwise fresh, healthy, green foliage and seal in a plastic bag. Add no water or paper towels! Keep the bag out of the sun and at indoor temperatures. Don’t refrigerate.
Contact Carol MacNeil, crm6@cornell.edu or 585-313-8796; John Gibbons at 585-394-3977 x405; or, another member of the Cornell Vegetable Program staff. It’s critical that foliage be fresh! (*See below if you can’t get the sample to us in a day or two.) We welcome good quality photos and can sometimes diagnose LB by photo. Take a photo of the field with the suspected LB spot. Also take a few close-up photos. (Some cameras can’t take clear close-ups so check your photos before sending them!) Photograph two to three leaves with lesions, stems with lesions, both upper and lower leaf surfaces, filling the frame with the leaves.
If LB is found destroy hotspots and a wide margin around them with a fast acting herbicide like Gramoxone, by repeated discing (thoroughly clean equipment before driving through uninfected areas!), or by cutting staked tomato stems at the soil line and several places up the stem. If LB is detected or suspected, or if spray intervals have been stretched, spray the affected field and those around it as soon as possible, preferably with a systemic or translaminar (movement from upper to lower leaf surface) fungicide specifically recommended for LB. Some of the best materials during this part of the season on potatoes and tomatoes are:
Excellent: Ridomil Gold Bravo, systemic, curative (use only if LB US-22 or US-23 have been identified – not effective against other LB strains).
Good:
Previcur Flex, systemic, curative; mix with a protectant Presidio, translaminar, curative (for tomatoes only!); mix with a protectant Fair (for Organic Production): Approved copper formulations, contact
See Tom Zitter’s potato and tomato attachments to this email for many other Fungicides, effectiveness ratings, and more details. See also the 2013 Cornell Vegetable Guidelines, Potatoes, Disease Management – Late Blight at: http://veg-guidelines.cce.cornell.edu/24frameset.html
For organic producers, see the 2013 Production Guide for Organic Potatoes at: http://nysipm.cornell.edu/organic_guide/veg_org_guide.asp
*Late Blight Sample Collection & Submission to Bill Fry, Cornell
Samples must be reported online and a form that is generated from your submission must be included with the sample. You will receive a sample number (which should be written on the sample bag when it is sent to the lab), and this number can be used to track your sample.
To Report online and fill out a form go to: http://www.usablight.org/report=
If you are new to the system you must Register for Sample Submission before Reporting, at: http://www.usablight.org/submit_registration
When sending late blight samples it is better to send leaf tissue rather than fruit or tubers. If you do send fruit or tubers send them in a separate bag or shipment — so they do not crush the leaf tissue in transit. What to send:
1. A minimum of 5 fresh turgid leaves with actively sporulating lesions. Smaller lesions are best. Collected from several locations when possible.
2. Place the foliage in an air-tight dry plastic (Ziploc) bag with a cushion of air – so the foliage doesn’t get crushed. Use a small shipping box rather than an envelope. PLEASE write the sample number on the bag.
3. Send the sample immediately upon collection. If you must “hold” the sample overnight, keep it at 40 – 50 F.
4. Include the completed sample submission form in the box with the sample.
5. Mail the sample via overnight mail to:
Bill Fry
334 Plant Science Bldg.
Cornell University
Ithaca, NY 14853
E-mail: wef1@cornell.edu
Office Phone: 607-255-7863
Lab Phone: 607-255-3188