Diagnosing Root Death In Woody Ornamentals

Root death is an important cause of poor health in woody plants. When roots are killed, the plant is unable to take up sufficient water or nutrients for development.
Diagnosing Root Death In Woody Ornamentals - Articles
Diagnosing Root Death In Woody Ornamentals

Lee Miller, University of Missouri, Bugwood.org

Generally, the above-ground symptoms appear long after root death has been occurring. As a result, it is difficult or impossible to treat the plant so that it recovers fully. However, an effort should be made to determine the reason roots were killed, particularly if the plant will be replaced. Although this can be a very difficult process, it is sometimes possible to identify the cause of root death by carefully observing signs of the problem. Below are some of the symptoms of root death, the signs that should be sought, and the questions that need to be answered in order to successfully diagnose the cause.

Symptoms Typically Occurring When Roots Are Dead

  1. Plant growth slows as compared to healthy plants. Determine whether the terminal bud scars from recent years are closer together than those from previous years.
  2. Leaves wilt or yellow and fall prematurely.
  3. Margins of leaves die in the summer (termed, marginal leaf burn or scorch).
  4. Roots appear dark brown or black and few or no white roots or root tips can be found when the roots are washed free of soil. *Note that some healthy plants (i.e. azaleas, rhododendrons) naturally have darkly colored roots.
  5. Roots are limp and not brittle and crisp as is found in healthy plants of all types.
  6. The plant has few small side branches or side branches are dead and only main branches are alive.
  7. The canopy of the plant is very asymmetric or misshapen because major branches are dead.
  8. During the winter, there is an extensive cankering and dieback of small twigs and branches.

Some Of The Above Symptoms Can Be Caused By

  1. Root rotting fungi. Look for conks, shelf-fungi, mushrooms, and 'deadman's fingers' growing on the butt, root flares, or main roots, particularly in late summer and early autumn. Fibrous roots may be black (Thielaviopsis). A fungus may form a sheath (white, Armillaria ; black, Xylaria) just under the bark. The fungus may form dark brown 'shoestrings' on or just under the bark (Armillaria). Or, the wood of the main roots and lower trunk may be black (Xylaria), black and resin soaked (Verticicladiella) or brown to reddish brown (Phytophthora). In elms, the wood just under the bark may be butterscotch-yellow and have the odor of oil of wintergreen (elm phloem necrosis = elm yellows). The wood of the root may be soft and decayed (Ganoderma, Polyporus, Inonotus, and others).
  2. Over-fertilization or deicing salt damage. Check with the owner to determine what has been done around the plant over the years. A tissue analysis may indicate excessive chloride or other ion indicative of a toxicity problem.
  3. Flooding or drought. Check drainage patterns in the vicinity and any recent changes made in the drainage pattern. Check local weather records.
  4. Root exposure to chilling or freezing temperatures or to excessive high temperatures. Determine when the plant was put in. If within a year, determine under what conditions the plants were maintained before, during, and soon after planting.
  5. Phytotoxicity due to insecticides, herbicides, and fungicides applied to the soil in the root zone. Check with the owner to determine what has been done around the plant during the last year or two. Assess the possibility that one or more of the chemicals on the list may be the source of the damage. Note that damage from certain herbicides may become obvious 1 or 2 years after treatment.
  6. Girdling roots or ropes. Look for roots, ropes or wires encircling the trunk. If the trunk is abnormally flat on one side at the soil line, dig below the soil line to look for a girdling root. Look for wires or ropes that were not removed at transplant but which now may be girdling the trunk.
  7. Planting or back filling too deeply. Be suspicious if there is no flare at the base of the tree.
  8. J-rooting conifers. Excavating the root system will reveal that the main root is in a J-shape and is not growing downward properly.
  9. Roots were unable to penetrate the native soil from the original transplant hole. Excavating the root system will reveal that the roots have not exited the original transplant hole significantly. The hole has acted like a flower pot possibly because a) the equipment used to create the transplant hole compacted the wall of the hole, or 2) the native soil is compacted or very difficult for the roots to penetrate (clay), or c) the back fill material is much more conducive to root growth than the native soil. As a result, a root volume sufficient to support top growth fails to develop.
  10. The plastic burlap material was not removed and roots were unable to exit into the surrounding soil. A lighted match will cause plastic burlap (which does not rot in soil) to melt while natural-fiber burlap (which rots in soil and allows roots to exit) will burn.
  11. Natural gas leaking into the soil from a broken pipe or gasses generated by a buried organic material, such as in a nearby landfill, displace oxygen and roots die. Have the gas company determine if a pipe is broken.
  12. Insect feeding can kill root tips or girdle larger roots. Excavating the roots will reveal chewing or tunneling damage from various insects or the larvae of insects will be found on or in roots.

Before any action is taken, a diagnosis must be made of the actual cause of the symptoms. If the damage is due to the activity of fungi such as Phytophthora and Thielaviopsis, fungicides are available which can check the fungus and allow the plant to grow. These fungi are not completely killed by fungicides. Some spores will remain alive within the infected roots. Therefore, repeated applications of fungicides are necessary. No fungicides effectively control Ganoderma, Inonotus, Xylaria, or Armillaria.

Regardless of the cause of root death and measures taken to alleviating the causes, full recovery of the plant may take several years. Damage occurred over several seasons and recovery may take just as long.

Prepared by Gary W. Moorman, Professor of Plant Pathology