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Bacterial Blight - Pseudomonas syringae pv. syringae   Slide Series, www.ipmimages.org  HOSTS: Lilac, cotoneaster,
ornamental and fruiting cherries,
plums, and privet. Vegetable
crops(e.g.-broccoli, pea) are susceptible to various subspecies of P. syringae. DESCRIPTION:
Symptoms
vary with the host plant. Leaf symptoms are small brown/black,
angular-shaped spots with yellow halos. Spots coalesce and entire
leaves may die. Infected flower clusters fail to open, turn brown and
excude amber-colored gum. Infected twigs turn black. Infection is
usually limited to new growth; stems one year or older seldom
have lesions. Amber-colored gum occurs on bark surface around sunken
cankers. Underneath cankers the inner bark is reddish brown and
streaked.LIFE
CYCLE: Bacteria
are spread from plant to plant by splashing water. Infection takes
place through natural openings and wounds. Canker development is
optimum at temperatures of 72-79° F. In slightly below freezing
temperatures, the bacterium forms an ice nucleus which disrupts plant
tissue and causes symptoms typical of frost or freeze damage. The
bacterium overwinters on plant surfaces. CONTROLS:Cultural: Cold-stressed and wounded plants are more susceptible. Avoid late-season fertilization with nitrogen, and early-season or fall pruning of susceptible species, especially white-flowered lilacs (prune after bloom!). Prune out infected branches or infected leaves (vegetable crop) on a hot, dry day. Sterilize pruning tools between cuts. Protect with an antitranspirant spray (10 Tbsp./gallon of water). When weather is warm (>70° F.), keep irrigation water off leaves and lower branches and trunk. Chemical: Spray Bordeaux Mix on woody perinnials as buds begin to break in the spring. Protect with copper sprays if rain and warm (65 – 75° F.) weather occur. For vegetable crops, treat seed with hot water or bleach and use 2 year rotations. On vegetable crops, protect from rain and frost with floating row covers. |
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