Wet weather fosters cherry and stone fruit tree cankers


Our prolonged wet, cool spring weather is likely to bring on canker disease problems in cherry and other stone fruit trees, according to Ross Penhallegon, horticulture agent with the Oregon State University Extension Service.

Look for patches of leaves that have grown out, died, but have not fallen from the bud, recommended Penhallegon. Cherry trees with fewer than normal leaves may also be symptomatic of canker problems.

If your cherry, peach, plum or ornamental cherries and plums exhibit this symptom, they may be suffering from an invasion of a bacterial disease called bacterial canker or gummosis, he said. The disease is caused by the bacteria Pseudomonas syringae.

These dead buds and limbs become evident as warm weather approaches. Tree branches may die in segments or entire trees may die.

Cankers form on the bark, girdling branches and limbs of older trees, or entire trunks of younger trees. The forming of gum is one symptom of bacterial gummosis, but much of the damage may occur without this symptom.

Royal Anne, Bing and Lambert are susceptible cherry varieties, he said. Corum and Sam are tolerant varieties.

Buds that fail to develop into flowers may have also been killed by the bacteria. This phase of the disease is called "dead bud." There are often dead patches of leaves. As with other aspects of Pseudomonas, a wet spring will produce more severe symptoms.

With good pruning and thorough spray programs, you can help severely infected trees heal from a canker infection.

Penhallegon recommends the following practices to help prevent and reduce the incidence of stone fruit cankers:

Prune dead wood back to where live growth has formed. Delay this practice until you see where the new growth has developed--well into summer. Between pruning trees, sterilize tools with denatured alcohol. Many cankers cease growth with the onset of dry weather. - Spray the trees at least twice with copper materials such as bordeaux 12-12-100, Microcop, or Kocide for best control. The first application should be as the fall rains begin or in early October. The second spraying should be in early January. Since the bacteria may have invaded the tree, these protective sprays are the most effective measure to fight disease. - Give damaged trees additional fertilizer during the growth season.

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Ross Penhallegon

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