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PLANT SANITATION

Plant sanitation is the removal and destruction of diseased or dead plant parts or plants as soon as noticed, so as to prevent or lessen spread of pathogenic diseases to other plants. Pathogenic diseases are those caused by disease organisms, such as fungi, bacteria, viruses, and nematodes. Most plant problems are not caused by organisms, but are caused by cultural and weather stress conditions. However, it is always a good idea to practice good plant sanitation procedures for several reasons. First, if a plant part died of a non-pathogenic cause (such as drought), there are disease organisms which could start to grow on the dead part and spread into living parts. Second, plants generally heal better if dead portions are removed. Third, plant appearance is improved.

Plant sanitation should be practiced wherever plants are grown - in the yard and garden, greenhouse, nursery, home and agricultural fields and plantations. Observe plants periodically so as to detect, remove, and destroy diseased or dead parts promptly.

PRUNING OF DISEASED AND/OR DEAD WOODY TWIGS AND BRANCHES:
Diseased and/or dead twigs and branches on trees and shrubs should be removed as soon as noticed, regardless of the time of year.
HOW TO IDENTIFY RECENTLY DISEASED AND/OR DEAD TWIGS AND BRANCHES:
Although twigs and branches which have been diseased or dead several years are generally obvious, those recently affected may be difficult to identify.

Diseased branches and twigs which are not yet completely dead can generally be identified by sunken areas in the bark, or by bark which is a darker color in some areas than the normal bark. Many times the sunken areas of bark are also a darker color than nearby, healthy bark. This is more apparent on the bark of young twigs and branches. Older bark may not show these signs. Foliage may be yellow or brown on the affected branch, and normal on the healthy portions of the plant.

If a young twig or branch is completely dead, the bark will generally appear wrinkled and/or discolored compared to healthy bark. There may also be an obvious area around the twig or branch where the dead, shrunken bark meets the thicker, living bark. As mentioned, the bark of older branches may not show any outward evidence of death. Of course, foliage on dead branches will also be dead or absent.

Sometimes all the foliage on a branch or twig may be dead, even though the branch or twig itself may still be healthy and alive. It is a good idea in questionable situations to use a knife to carefully cut or scrape through the bark to the wood to see if the twig or branch is truly diseased and/or dead, and where the affected part ends. If the inner bark is green (red or pink in some flowering ornamental trees), it is alive and healthy at that point. If it is brown, then it is diseased and/or dead at that point. Make enough cuts to determine the overall condition of the twig or branch, and if diseased or dead, to find where the affected part ends. Remember, if a disease organism has caused the problem, and you cut into the diseased or dead area, the disease organism will then be on the knife or other tool, and could be spread to still living, healthy areas, if they are then cut into. Sterilize the cutting tool as described below, before using it on any healthy plant parts.

PRUNING PROCEDURES:
Branches and twigs should be pruned at a side branch, or flush with the main branch, or trunk, depending on where the diseased or dead portion is located. The pruning cut should be made in living, healthy tissue at least several inches below the margin of the diseased or dead area, so that all of the affected part of the twig or branch is removed, The cut should be smooth, to promote quick healing.

If any diseased, dead bark or wood is cut into before the final pruning cut is made in the healthy tissue, the cutting tool should be sterilized before it is used on healthy tissue. For information about sterilizing tools, see Dr. Linda Chalker-Scott's articles at http://www.puyallup.wsu.edu/~Linda%20Chalker-Scott/Horticultural%20Myths_files/Myths/Pruning%20tools.pdf

Cankers on trunks or on branches too large to prune, may be removed surgically by chiseling or gouging. Try to remove 1/4-1/2 inch additional healthy bark and wood surrounding the canker area, keeping the above sanitary procedures in mind. This is to ensure that all diseased bark and wood are removed. However, surgical removal of cankers is sometimes not very effective. It may be difficult not to spread the organism within the wounded area as the canker and adjacent healthy wood and bark are being cut out, and sometimes the branch or trunk is so weakened that it may break. Decay organisms may easily enter the resulting large wound.

Branches and twigs which have been removed, as well as any chips and shavings, should be placed in the garbage, taken to the dump, or burned. Do not compost them and do not leave them laying around.

Recent evidence indicates wound dressings are of no value, and may actually accelerate decay of the wound. Covering wounds with black plastic is reported to improve wound healing and decrease decay.

REMOVING OTHER KINDS OF DISEASED AND/OR DEAD PLANT PARTS:
Other kinds of plant parts, such as leaves, flowers, tender shoots, etc., sometimes die or become diseased or decayed, and should be removed as soon as noticed, This applies to all plants, including houseplants. Many times the parts are tender enough to be removed with fingers, but pruning shears may be needed. If hands are used, wash them before handling healthy plants. Pruning tools should be sterilized as outlined above. The removed plant parts should be placed in the garbage or burned (if you are in an area where burning is allowed). Do not compost them, and do not leave them laying around. This applies also to fallen leaves which are diseased.
REMOVING COMPLETELY DEAD PLANTS:
Plants, including trees and shrubs, which have completely died or are about to die, should be entirely removed, including the root system, and placed in the garbage. This is a good precaution to take in case of pathogenic root rot. (Annual plants which normally die each autumn, need not be destroyed if they died at the normal time, and if there is no reason to suspect any problem). Often it cannot be determined if a pathogenic root rot was responsible for the problem. In cases where pathogenic root rot is suspected, but not positively diagnosed, the below precautions should be followed. Remember, most plant problems are not caused by disease organisms. A plant may have died because of drought, winter cold, or poor soil drainage.

If a pathogenic root rot (such as caused by a fungus) has caused a plant to die, the soil as well as the plant will be contaminated with the organism. The following additional precautions should be taken:

  • Do not move contaminated soil to other areas as this will spread the organism. Be careful of soil clinging to shovels, stakes, etc.
  • After removal, sterilize as outlined above, the tools used in removing and cutting up the plant.
  • Pick up and destroy all wood chips, root pieces and other debris resulting from plant removal.
  • Do not plant the same kind of plant or a related plant in the contaminated area unless the area is completely replaced with uncontaminated soil.
  • For potted plants, place the entire plant and pot in the garbage or place the plant and the soil in the garbage, and wash and sterilize the pot and saucer. Any tools, pots, stakes etc., used in the contaminated soil should be sterilized, or placed in the garbage.
Written by Rick Reisinger, retired WSU Extension Agent

6/85 reprinted 2/95 slightly revised 11/07dp