![]() Note: Organic producers may be interested in an article by Meg McGrath (Cornell University) on managing late blight in organically-produced tomato. You can review previous Veg Crop Update articles on late blight in the ONvegetables archives. It is important to scout your fields regularly and know the symptoms of late blight. If the weather conditions become dry, the spray intervals may be extended. Pyraclostrobin (Cabrio) – use high rate for late blightĭuring wet cool periods, a fungicide should be applied every 5 – 7 days to protect against late blight. Mandipropamid (Revus) – has some translaminar movement Dithane DG, Manzate Pro-Stick, Penncozeb 80 WP)įamoxadone + cymoxanil (Tanos 50 DF) – has some kickback activity Recommended protectant fungicides for tomato late blight in Ontario: Remember that conventional tomato growers following a regular fungicide spray program (by calendar or TOMcast) for early blight, septoria leaf spot, and anthracnose, are also protecting the crop from late blight infection. Late blight can devastate a tomato crop very quickly if conditions are favourable. Tomato growers should implement a protectant fungicide program immediately and scout their fields carefully. This may indicate that late blight spores have reached much of southern Ontario. Reports of late blight were also received from another location near Simcoe and one near Milton. Yesterday (August 4), late blight was confirmed in tomatoes near Simcoe, Ontario and in potatoes in the Alliston area. Overhead irrigation can promote foliar fungal disease due to longer periods of leaf wetness.Janice LeBoeuf, OMAFRA Vegetable Crop Specialist, Ridgetown.Cultivars vary in tolerance to early blight.Ensure transplants are healthy and free of disease.Reduce early blight inoculum by following a 3 to 4 year crop rotation.Application should continue until close to harvest. Extend the schedule to 12- 14 days in warm, dry weather if diseases are under control. Repeat at 5- 7 day intervals during continuous moist weather. If this is unavailable, begin a preventative spray program when the first fruits are about walnut size. Unless the fungus is present on transplants, lesions generally don’t show up until flowering. Temperatures of 17- 24☌ (63- 75☏) and extended leaf wetness favour early blight development. Spores are present throughout the growing season and may be carried long distances in the wind. It is spread by wind and splashing water. The fungus that causes early blight survive on decayed plant material in soil and can be seed borne. Lesions may also appear on stems and blossoms (a cause of blossom drop).įruit infection is uncommon, showing up as a blackened area, similar in appearance to blossom-end rot, but at the stem end of the fruit or as blotches or sunken areas (see Black Mold). Lesions may coalesce to form large dead areas on the leaf. They are often bordered by leaf veins.Įarly blight may cause browning of leaf edges. As lesions enlarge, their shape may become irregular. If the disease is severe, lesions also appear on younger leaves. Lesions become quite large and are often associated with considerable leaf yellowing. The tissue surrounding the spot may be yellow. Spots are circular to angular with dark concentric rings (target spot). Lesions first appear on leaves as dark brown to black spots, 8- 13 mm (5/16- 1/2 in.) in size, on older foliage, but can grow much larger. The first signs of disease often appear deep in the canopy where the leaves stay wet. Applications should continue until close to harvest. ![]() Temperatures of 17- 24☌ (63- 75☏) and extended leaf wetness favour early blight development.Įarly blight lesions can be distinguished from other lesions on the foliage by the presence of concentric rings. Spores are present throughout the growing season and may be carried long distances in the wind or spread by splashing water. Septoria Leaf Spot (Early blight lesions grow much larger than Septoria lesions.)Įarly blight overwinters in infected crop residue and can be carried by infected seed and weed hosts. Fruit infections are not common, but may appear as a blackened area at the stem-end or dark blotches and sunken areas (see Black Mold)īacterial Canker (Early blight may cause browning of leaf edges, similar in appearance, but a lighter brown than bacterial canker symptoms.).Lesions become quite large and are often associated with considerable leaf yellowing. ![]()
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