Tomato Plants - Bacterial canker and Late blight
Monday, 24 May 2010 14:17
Be on the watch for Bacterial Canker Clavibacter michiganensis pv michiganensis and Late Blight caused by Phytophthora infestans. These two diseases can be very destructive to tomatoes in
Initial symptoms of Bacterial Canker are the result of primary, systemic infection that first affect the lower leaves causing leaf curling, wilting, chlorosis, and shriveling. In advanced stages, the pathogen spreads throughout the plant and causes poor growth, wilt, and plant death. Foliage throughout the canopy wilts, yellows, turns brown, and collapses. Stems can split resulting in open breaks or cankers and stems break easily. Secondary infections occur from water splash onto foliage, stems, and fruit. Spots occur on green fruit and are very characteristic: white to yellow spots, 3-4 mm with raised brown centers (“bird’s eye spots”).
Late blight appears on potato or tomato leaves as pale green, water-soaked spots, often beginning at leaf tips or edges. The circular or irregular leaf lesions are often surrounded by a pale yellowish-green border that merges with healthy tissue. Lesions enlarge rapidly and turn dark brown to purplish-black. During periods of high humidity and leaf wetness, a cottony, white mold growth is usually visible on lower leaf surfaces at the edges of lesions. In dry weather, infected leaf tissues quickly dry up and the white mold growth disappears. Infected areas on stems appear brown to black and entire vines may be killed in a short time when moist weather persists.
Note: The symptoms for Bacterial Canker and Late Blight most often do not appear early in the growing season, but can be introduced and symptoms noticed on plants grown and shipped to New England from the south.
Photo: Cut stem of a potted tomato plant with Bacterial canker
Late Blight information and photos (scroll down for photos)
Paul Lopes, University of Massachusetts
