Sick Plum tree

Asked July 6, 2019, 11:05 PM EDT

The last few years I have been getting little to no fruit off my tree. It blooms each year but then turns brown and crunchy. There are leave on most of the branches but some parts do not get any leaves. I am not sure what is wrong with it or how to fix it. Any recommendations of what I should do is greatly appreciated. Thanks, Shelby

Clackamas County Oregon

1 Response

Your tree may be suffering from Pseudomonas syringae pv. syringae, a bacterium. Two common genetic traits increase the bacteria's ability to cause disease. Most produce a powerful plant toxin, syringomycin, which destroys plant tissues as bacteria multiply in a wound. Bacteria also produce a protein that acts as an ice nucleus, increasing frost wounds that bacteria easily colonize and expand. Factors that weaken or injure the tree predispose it to developing cankers. Factors include wounds, frost damage, early pruning, soil pH, poor nutrition, and infection by other pathogens including Verticillium, Nectria, and nematodes. Sources of bacteria include old cankers, healthy buds, systemically within trees (with or without cankers), as epiphytes on leaf surfaces, weeds, grasses, and even soil. Wind, rain, insects, infected bud wood, and infected nursery stock can spread bacteria.

Symptoms The most conspicuous symptoms are cankers, gum exudation, and dieback of girdled branches. Dead buds and leaf spots also can occur. In most cases, heavy gumming is associated with bacterial canker formation on branches and twigs. Gumming occurs at the cankers' margins. Other problems can lead to gumming {see Cherry (Prunus spp. - Gumming)}.

Cankers caused by the bacteria may be on the trunk, limbs, and twigs. Typical cankers are much longer than broad, but a canker may girdle the infected limb or trunk. The cambium at the canker will be discolored and necrotic. Use a pocket knife to reveal this discolored tissue. Cankers develop in winter and early spring. As the tree begins growth in spring, the bacteria population declines and a callus layer forms around the canker's edge. During spring and summer, girdled and nearly girdled limbs may leaf out. Normally, leaves turn yellow, then the limbs usually die. In some instances, these symptoms may not appear until late summer when the leaves' water requirement is high.

Dead bud "disease" is first noted as dying buds on spurs in spring. Infected buds usually start to die in February. As the disease progresses, both leaf and flower become infected. Dead bud usually starts in lower limbs and moves up the tree and to adjacent trees in successive years. Often, trees in the lower orchard, where air drainage is poor, are the first to be infected. If all buds on a spur are killed, the spur will die back next season. Cankers very seldom form, but the diseased buds may produce a slight gumming. Repeated death of buds may result in misshaped growth and sometimes fasciation. In severe cases, 90% or more of buds on a tree may be killed.

Leaf and fruit spots are not common and are not numerous if they develop. Spots on leaves are at first water soaked, then become dry and brown. Spots on fruit are dark to black and depressed or pitted.

Cultural control Bacterial canker is best managed through the use of many different tactics.

  • Plant resistant cultivars and/or rootstocks.
  • Do not interplant new trees with old trees, which are a major source of the bacteria.
  • Locate orchard in an area less likely to be affected by frost. If planting in the spring, plant orchards after date that frost is likely to have occurred. Prevent winter injury by painting trunks white and avoiding late season fertility.
  • Test soil for ring nematodes before planting. Also test for pH and other physical characteristics that can be corrected prior to planting.
  • Provide optimal soil conditions including attention to pH and nutrition. Annually monitor for adequate nutrient levels such as nitrogen. Keep irrigation off above ground parts for the first few years.
  • Control weeds.
  • Delay dormant pruning until January or February. Summer pruning is even better and should be after harvest, when weather is dry. Make heading cuts after planting only during dry weather when rain will not occur for at least a week after pruning. Make heading cuts close to a lateral bud.
  • Completely remove infected trees or branches girdled and killed by cankers. Do not allow trees to regrow from roots or trunks left after a major trunk canker has been removed.
  • In summer, small cankers may be cut out using the following method. Cut away bark above and around the edges of the infected area. Use sharp tools, and leave wound margins smooth and neat. Wounds should be left uncovered to dry out during the summer. Try not to have sprinkler irrigation soak the wounds.

Hope this helps!