Diseases of trees
Trees, like any living organism, can catch a disease:
- Every gardener had unpleasant surprise to see the leaves of a tree fading or fruits to hesitate to mature or strips the bark shedding off abnormally.
Riot is visible but it hides an internal riot.
Diseases of trees are due to pathogenic agents as worms, mushrooms or viruses. Some diseases are lethal, as Dutch elm disease. Moreover, they are contagious and if not eradicate the cause, it is appropriate to limit the spread by slaughter of affected individuals. A mushroom, Ceratocystis, attacks plane trees in the south of France, while one other (cardinal Coryneum) decimates cypresses in Italy of the South and of the Centre. In California, the cypress of Monterey is threatened. In the Southwest of Australia, a particularly virulent illness destroys eucalyptuses. In Morocco, Jamaica and Florida palm trees and date palms are destroyed by a disease, spread by a fungus, Fusarium sp..
- As in living organisms, an illness detected enough early can be fought by an adapted treatment. Still it is necessary to make good diagnosis and to apply the corresponding treatment.
- The diagnosis is based on outward signs and their evolution, including the bursting of the bark, or showing symptoms of the reaction of the tree to disease, premature wilting or yellowing leaves. These early findings are often sufficient, but sometimes you have further investigation with laboratory analysis of a sample of bark, leaf or root portion. Analysis (enzyme immunoassay, or polymerase chain reaction) are comparable to those performed with a blood sample to detect diseases in humans.
Once the disease is recognized, treatment can be developed, based spray chemicals (fungicides, pesticides, insecticides, ...) or natural (such as Bacillus thuringiensis).
Let us remind that the use of chemicals is not an insignificant act: it is necessary to respect minimal rules, to protect one's hands, not to leave products within reach of children,
It is necessary to use it wisely by knowing risks on environment. The honeybees suffer from the deltamethrin, for example. The abuse of products can contaminate ground waters. Besides some products were withdrawn from commercialization because it has been admitted it was harmful (they are listed "Produced Phytosanitary not Usable").
to go farther : http://www.apsnet.org