Cherry tree disease: bacterial canker
What is it?
Bacterial canker is a plant disease which has two other names. Bacterial canker in cherry trees is also known as bacterial blast and may be referred to as bacterial gummosis. Although it is a prime and severe attacker of cherry trees, bacterial canker also attacks a wide variety of both fruit and nut trees. This disease, whether called bacterial canker, bacterial gummosis, or bacterial blast in your region is caused by the bacterium pseudomonas syringae. Bacterial canker is active in all phases of the growing season for cherry trees but can be most devastating to young trees which are more susceptible to damage from pseudomonas syringae bacterium.
What does it look like?
The bacterial canker disease first appears as yellow and green leaves discoloring. These leaves then fall off the cherry tree to reveal weakened limbs. Often the cherry tree leaves drop prematurely, but in some regions the leaves may discolor, then brown and wilt. Eventually these leaves will wither and may even remain attached to the cherry tree throughout the winter if they do not drop from the cherry tree in the fall. The bark of the cherry tree has lesions on it which often ooze an amber to yello colored gum from their centers. This oozing of bacterial gum is most common in the seasons of spring, fall and winter. Oozing may be particularly severe during the spring, especially if your region has cool, moist temperatures. Bacterial canker prefers cool, moist conditions, even wet conditions, and it is during periods of these climate conditions that bacterial canker will cause the blossoms to wilt, wither, die and drop off of the cherry tree. As the bacterial canker spreads, entire limbs may become weakened and die off or extreme amounts of defoliation may occur on the infected cherry tree. Occasionally the fruits will develop dark, sunken lesions or the leaves may develop angular holes in them before wilting and falling off the cherry tree.
How does it manifest?
Bacterial canker is known for its characteristic oozing of gum from the many cankers which infect susceptible cherry trees. Splashing rain and wind causes this gum to spread in the early spring as temperatures begin to warm, but still remain moist and wet. These conditions are the perfect environment for pseudomonas syringae bacterium to spread rampantly. Initial infection, if not from the spread of gum occurs when the gum enters an existing wound in the tree, such as a pruning cut on a twig or branch. Often bacterial decay of another sort may cause the initial canker to form and it is easily infected by the spreading ooze of pseudomonas syringae. When summer hits your region, spread of bacterial canker will slow down due to the warmer temperatures. However, cankerous lesions will still develop, albiet slowly over this period and by midsummer you will see a marked die back of affected twigs, limbs and branches on cherry trees. Once temperatures become cool and wet again in the fall, spread of the disease picks up pace once again and bacterial activity increases to do some of the most devastating damage to cherry trees.
What can you do about it?
Unfortunately, bacterial canker in cherry trees is incredibly difficult to control. Your best efforts at pruning out cankerous branches can be useless unless you carefully apply alcohol to your pruning sheers to sterilize them with each cut. This action helps to prevent pruning wounds which can easily become reinfected with pseudomonas syringae and other bacterium. Other than removing the affected areas of the cherry tree during the growing season, there are no real control mechanisms. However, once fall hits your region you can spray the cherry tree with a basic copper containing fungicide which will help prevent additional infection and keep your cherry tree healthy. However be sure to prune, off or out, all visible cankerous areas and destroy the debris carefully.
Cherry tree disease: bacterial canker
Lauri Jean Crowe
© 2002 Pagewise
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