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Tree diseases are caused by infectious or living organisms such as fungi, viruses, and bacteria. Disorders, which can exhibit disease-like symptoms, are caused by noninfectious or nonliving agents such as nutrient deficiencies, temperature extremes, vandalism, or pollutants.
A pathogen is present (disease-causing agent).
A plant is vulnerable to that particular pathogen.
The environment is conducive to disease development.
Often considered a "secondary problem" to environmental stress, insects can retard plant growth, weaken tree structure, and spread plant diseases by feeding on trees.
Chewing insects, like beetles and caterpillars, eat leaves, flowers, and twigs. Discoloration and uneven or broken edges are signs that chewing insects might be present.
Sucking insects, like aphids and mealybugs, feed on sap within the plant. Damage is indicated by the discoloration, drooping, and wilting of leaves, and the presence of honeydew.
Boring insects, like bark beetles, feed beneath the bark of the tree as larvae. Most borers are attracted to, and successfully attack, stressed trees often killing them.
"Just because you find an insect on a plant does not mean thats the one causing the damage," said Fred Miller, Joliet Junior College in Joliet, IL. While some insects can threaten tree health, many are helpful and actually rid trees of dangerous or harmful insects. "For example, many people think the lady bird beetle is harmful, but they actually eat aphids, which are the insects that really harm trees and plants."
Correct diagnosis of plant health problems requires careful examination of the situation. The ISA offers these tips to aid in your assessment:
Accurately identify the plant. Insects and disease are plant-specific, limiting the number of suspected pests.
Look for a pattern of abnormality. Compare the affected plant with others on the site, especially those of the same species.
Carefully examine the landscape. The history of the property and the adjacent land may reveal many problems.
Examine the roots. Note their color. Brown or black roots may signal problems.
Check the trunk and branches. Wounds in the trunk can provide entrances for pathogens and wood-rotting organisms.
Note the position and appearance of affected leaves. Dead leaves at the top of the tree are usually the result of environmental or mechanical root stress. Twisted or curled leaves may indicate viral infection, insect feeding, or exposure to herbicides.
Treatment depends on the particular insect or disease problem, the species of plant or tree affected, the extent of the problem, factors specific to the environment, and local regulations. Homeowners who have doubts about how to proceed should consult a certified tree care professional for advice.
For more information on insects and disease visit www.treesaregood.org.
The International Society of Arboriculture (ISA), headquartered in Champaign, Ill., is a nonprofit organization supporting tree care research and education around the world. To promote the importance of arboriculture, ISA manages the consumer education web site, www.treesaregood.org. Also, as part of ISAs dedication to the care and preservation of shade and ornamental trees, it offers the only internationally-recognized certification program in the industry. For more information on ISA and Certified Arborists, visit www.isa-arbor.com.
Courtesy: Home Improvement News and Information Center
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