From OMAFRA’s ONvegetables.com
By Janice LeBoeuf
To date, I know of no confirmed cases of late blight in Ontario or nearby states, but there’s a report today of it showing up in Wisconsin. Nevertheless, our experience of recent years would indicate we are likely to see it in Ontario tomatoes at some point in the season.
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, tomato growers should:
- 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 the Tomato Late Blight Photo Gallery and Late Blight Look-Alikes for photos of late blight and possible look-alikes on tomato.
- chlorothalonil (Bravo, Echo) – contact fungicides – have been very effective protectants in tomato
- mancozeb (Penncozeb, 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 mate