How to Recognize, Manage and Prevent Crown, Collar and Root Rot on Orchard Trees

Phytophthora root and crown rot,
Phytophthora root and crown rot,
Severe crown and collar rot on fruit tree.
Severe crown and collar rot on fruit tree.

No Growing Zone Is Safe From This Disease

  • Regardless of your growing zone, you could be facing crown and collar rot, a horrible disease that affects apple trees and other orchard trees. This disease is particularly disturbing up in Washington state where I live, as there are so many orchards and lots of rain. This disease is usually common in plants that are always wet at the soil line between spring and fall (and if you've ever been to Washington state, you know that rain is one of the things you will remember most about this area).
  • Trees become infected during wet weather when fungus manages to survive in the soil or debris. Resting spores can survive under those conditions as well as in infected plant tissues.
  • This disease is caused by the Phytophthora cactorum species.

Hosta Crown Rot

...even your beloved hosta plants are safe from this disease.
...even your beloved hosta plants are safe from this disease.

Kopachuck State Park in Washington Lost Hundreds of Trees

In 2012, hundreds of infected trees had to be cut down in the Kopachuck State Park in Washington State.
In 2012, hundreds of infected trees had to be cut down in the Kopachuck State Park in Washington State.

How to Recognize Crown, Collar and Root Rot

  • The symptoms of this disease will vary and early symptoms are particularly hard to detect.
  • You can expect collar rot to affect a tree above the soil line (usually in the area of the scion - detached shoot or twig containing buds from a woody plant, used in grafting). Crown rot, on the other hand, affects a tree below the soil where the roots join the stem, the crown being the area above the trunk, where succeedingly smaller and smaller branches, stems and twigs will form.

    Root rot, of course, affects the roots of a tree.
  • If your tree has severely infected buds, they will swell and break dormancy. Appearances will be deceiving, as they will appear to emerge normally in the spring, but then will wilt. The entire tree usually collapses when there is severe infection. The leaves on some of the branches turn to purple, yellow or bronze and the tree bark darkens. Normally, the layer of tissue under the bark is white or a very light green, but an infected tree will have a dark brown cambium - the thin layer of generative tissue lying between the bark and the wood of a stem, most active in woody plants.
  • Trees that are infected with root rot can be easily blown over by strong winds (see photo).
  • A canker (usually purple to black color) is often observed at the base of an infected tree and yellow leaves will appear with symptoms that resemble an iron deficiency.
  • To properly diagnose, you will need to remove the soil from around the crown and roots of dying or dead trees. Then, scrape away the bark along the trunk of the base of the tree and its roots. Here's what to look for:
  • Orange to dark reddish brown canker or streaks along the cambium of the collar or crown at ground level or just under the epidermis of the roots. This canker is often limited by a dark margin which separates it from the healthy tissue.
  • Fruit may appear on only the upper branches of the tree, and a mature tree may continue growing even though weakened, or it may die. A young tree will usually decline rapidly and die.
  • For positive identification,you would need to send a sample of the diseased roots or crown tissue to a qualified pest diagnostic laboratory, but once you start scraping away the back it should be pretty evident.

Diseased Tree With Collar Rot

How to Manage Crown, Collar and Root Rot

You must constantly inspect your trees for the signs mentioned above. In the summer, you should scrape off any diseased tissue and move the soil away from the trunk. This will leave the crown exposed to air, and you should leave it that way until the fall. Be VERY careful during inspection not to damage the crown.

How to Prevent Crown, Collar and Root Rot

  1. Avoid overwatering
  2. Plant new trees on an elevated area to avoid damage from heavy rain
  3. During inspection, be careful not to wound the tree crown

Sorry, but there are no truly resistant varieties of trees, but you should always check with your local cooperative extension service to see if there are trees that have moderate to high resistance to this type of disease.

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