Updated June 16, 2014 to include new fungicide registration.
To date, there are no confirmed cases of late blight in Ontario, but the disease has shown up in neighbouring states. Here’s a summary:
- July 17 – Wayne County, northern Ohio – tomato
- July 17 – Genesee County, (near Buffalo) New York – potato
- July 14 – Lancaster County, SE Pennsylvania – tomato
- July 13 – Allegan County, SW Michigan – potato
- July 11 – Madison County, (near Syracuse) New York – potato (US-23)
- July 10 – Erie County, (near Buffalo) New York – tomato (US-23)
- July 9 – Erie County, (near Buffalo) New York – potato (US-23)
- Late blight has also been confirmed in Wisconsin (July 3, potato and tomato), Massachusetts (July 11, tomato), New Jersey (July 4, potato, US-23; July 4, tomato; June 28, tomato), and several states further south.
Remember that conventional tomato growers using a recommended fungicide program for early blight, septoria leaf spot, and anthracnose, are also protecting the crop from late blight infection. Cloudy and high humidity or wet conditions are favourable for late blight. The pathogen prefers cool temperatures. The disease is suppressed by hot, dry weather, but it can continue developing and spreading when suitable conditions return.
If late blight is found in the area:
- Tighten up spray intervals – During wet cool periods, a fungicide should be applied every 5 – 7 days to protect against late blight. If the weather conditions become dry, the spray intervals may be extended.
- Scout fields often. Know the symptoms. Refer to Late Blight Look-Alikes for photos of late blight and possible look-alikes on tomato.
Figure 1. Late blight symptoms on tomato leaves appear as water soaked grey-brown lesions often surrounded by a light green or yellow halo.
Figure 2: Early late blight symptoms on tomato
- chlorothalonil (Bravo, Echo) – contact fungicides – have been very effective protectants in tomato
- mancozeb (Manzate, Dithane), metiram (Polyram) – contact fungicides – have been very effective protectants in tomato
- Acrobat 50 WP – translaminar – has some ability to move into the plant – must be tank-mixed with another late blight fungicide from a different chemical family – can add to the fungicide program, but rotate chemistries
- Cabrio EG – translaminar – has some ability to move into the plant – strobilurins generally rated lower than the other targetted late blight materials by researchers
- Presidio – translaminar, some “kickback” activity – registered (in tank mix with Bravo), but note that after using it, rotation to any crop except brassica (head and stem), bulb vegetables, cucurbit vegetables, fruiting vegetables, leafy vegetables (except brassica), root and tuber vegetables (except carrot and sugar beet) is prohibited
- Ranman 400SC or Torrent 400SC – protectant, locally systemic – should be tank-mixed with a non-ionic or organosilicone surfactant
- Reason 500 SC – locally systemic and translaminar – has some ability to move into the plant – must be tank-mixed with mancozeb or Bravo 500
- Revus – translaminar, some “kickback” activity – have some ability to move into the plant – can add to the fungicide program, but rotate chemistries and use in combination with protectants for resistance management
- Tanos 50 DF – translaminar, some “kickback” activity – have some ability to move into the plant – can add to the fungicide program, but rotate chemistries and use in combination with protectants for resistance management
- Tattoo C – systemic + protectant, some “kickback” activity – has some ability to move into the plant – includes a systemic ingredient plus a protectant ingredient from a different chemical family
- Zampro – two active ingredients – protectant and systemic, translaminar – can move into the plant
Past OMAFRA articles on tomato late blight are found under the late blight tag to the right. Please report any occurrences so that we can keep the tomato community informed about its development and spread and so that we can collect samples to learn about the strains, fungicide sensitivity, and the biology of this evolving disease.
Contact OMAFRA at 519-674-1690 or email@example.com if you suspect you have found late blight in Ontario. Those in the US can contact their state cooperative extension service or report online at http://www.usablight.org/.
Note: Organic producers may be interested in an article by Meg McGrath (Cornell University) on managing late blight in organically-produced tomato. Note that crop protection products mentioned in her article relate to US registrations. Consult the Canadian labels and your organic certifier for registered products that can be used in organic production.