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Plant sanitation can be useful in controlling plant diseases. It involves the removal and destruction of diseased or dead plants or plant parts as soon as noticed. This will lessen or prevent the spread of disease organisms (fungi, bacteria, viruses, nematodes). Plant sanitation must be done properly or disease organisms can be spread by incorrect practices.
Removing Diseased or Dead Woody Plant Parts
Remove these whenever noticed but do not prune in wet weather.
Identifying Diseased or Dead Twigs and Branches
Twigs and branches which have been diseased or dead for several years are generally obvious because of rotted or missing bark or wood, or lack of leaves. Those which have recently become diseased or died may be difficult to identify. Bark of young twigs and branches may have sunken, dark, or wrinkled areas. Older bark may not show these symptoms. Foliage on the affected twig or branch may be healthy, yellow, brown, wilted, or absent.
Sometimes foliage is dead, discolored, or absent, even though the branch or twig itself is healthy. Use a knife to make a small cut through the bark to the wood. If the inner bark is green (red or pink in some flowering ornamentals), it is healthy at that point. If brown, it is diseased or dead at that point. Make enough cuts to determine the overall condition of the twig or branch. If diseased or dead, find where the affected part ends by making several cuts.
Pruning
Make the pruning cut in healthy bark and wood at least several inches below the margin of the diseased or dead area. Prune at a side branch, bud, main branch, or trunk, depending on where the diseased or dead portion is located. Make a smooth cut to promote wound closure. Examine the cut surface for discolored inner bark or wood. If discoloration is observed, sterilize the cutting tool and make another cut to remove all the diseased area. Many times a branch will have a branch collar (ridge of living bark) at its base. When removing such branches, prune where the branch meets the collar. Do not cut the collar.
Performing Surgery on Large Branches and Trunks
Removing cankers (dead, discolored, sunken, or missing bark areas) by pruning out the twig or branch as described above is preferred. Surgically removing cankers by chiseling or gouging is sometimes suggested if the canker is on the trunk or a main limb. Removal of 1/4-1/2 inch of additional healthy bark and wood surrounding the canker is generally suggested. However, surgical removal of cankers may not be effective except with small, shallow cankers. Surgery is not suggested on large cankers. It is difficult not to spread the disease organism in the wound during surgery, and the branch or trunk may be so weakened that it breaks. The naturally formed decay barriers in the wood are broken, and decay organisms easily enter the wound.
Treatment of cavities in trees (removing decayed wood and filling the cavity) is not recommended. It will probably not eliminate decay or be of any other help to the tree and may break the natural decay barriers. Do not drill holes in cavities to drain water from them. Drilling breaks decay barriers allowing decay to spread.
Covering wounds Removing Diseased or Dead Non-Woody Plant Parts
Wound dressings may be applied, but recent evidence indicates they are of no value, and some may accelerate wound decay.
Plant parts such as leaves, flowers, or tender shoots which die or become diseased should be removed as soon as noticed. Rake up and destroy fallen, diseased leaves. Follow the applicable pruning, sterilizing, and disposal procedures.
Removing Completely Dead Plants
Trees, shrubs, and other plants which have died or are about to die should be removed entirely, including the root system. See disposal procedures on the last page. Such plants could have root rot or similar problems caused by disease organisms. If a disease organism is involved, the soil and plant are contaminated with the organism. Precautions in addition to plant removal and disposal should be taken.
Sterilizing Tools
If a diseased or dead plant part is cut, the disease organism will probably be on the tool and could be spread to healthy parts when cut. Thus, sterilize tools (shears, knives, saws, chisels, axes, etc. by washing in soap and water and swabbing in rubbing alcohol) before using on healthy plant parts . Allow to dry. If practical, contaminated shovels and other digging tools should be sterilized. If not, wash them. If hands are used to pinch off or handle affected plant parts, wash hands before handling healthy plant parts.
Disposing of Diseased or Dead Plants and Plant Parts
Whole plants, branches, twigs, chips, shavings, root pieces, and other plant debris should be placed in the garbage, burned, or taken to the dump. Do not compost them. Diseased fallen leaves and needles should also be destroyed. Annual plants which normally die each autumn need not be destroyed if there is no reason to suspect any problem.
For more information contact your local WSU Extension Office.
By Roy M. Davidson, Jr., former Agricultural Research Technologist, and Ralph S. Byther, Extension Plant Pathologist, WSU Puyallup. Washington State University Extension Bulletin 1237. Slightly revised October 1991.
