Insects and disease prey on stressed trees
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Sufficient water, light and a proper balance of nutrients greatly
influence plant health. Too much or too little of any of these
environmental conditions may cause plant stress, which can weaken
trees and make them more susceptible to insect and disease attack.
Therefore trees require proper plant health care. "We all love being
surrounded by nature; however, to create that natural feeling in
urban settings, we need to give trees a little help because they are
growing in unnatural conditions," says Jim Skiera, executive
director of the International Society of Arboriculture.
Diseases and disorders
Diseases are caused by infectious or living agents such as fungi,
viruses and bacteria. Disorders are caused by noninfectious or
nonliving agents such as nutrient deficiencies, temperature
extremes, vandalism and pollutants. For a disease to develop, there
must the presence of a disease-causing agent (pathogen) to which the
plant is vulnerable. If the proper environmental conditions are
present over a certain amount of time, then the pathogen will infect
the plant. For example, many fungal diseases require moist
conditions for spores to germinate.
In many cases, insect problems are secondary to problems brought
on by a stress disorder or pathogen. Focusing on getting rid of the
pest might not solve the primary problem.
Some insects suck sap from the tree or bore into the trunk and
branches. These insects can stunt tree growth and weaken its
structure. Insects may be divided into three categories according to
their method of feeding.
such as beetles and caterpillars, eat leaves, flowers and twigs.
Indications of damage by these insects include leaf notching or
such as aphids and mealybugs, feed on sap within the plant.
Drooping, wilting and discoloration are some indications of
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such as bark beetles, feed beneath the bark of the tree as
larvae and continue to reproduce within the bark. Adults may lay
eggs in tunnels beneath the bark. Boring insects tend to be the
most destructive and can kill trees.
The most important thing to remember is that many insects in the
garden or landscape are beneficial rather than destructive. They
help with pollination or act as predators of more harmful insects.
Therefore, killing all insects without regard to their species and
function can actually be detrimental to plant health.
Diagnosis and treatment
Correct diagnosis requires a careful examination of the
situation. You must accurately identify the plant; look for patterns
of abnormality; examine the roots, trunk and branches; and note the
position and appearance of any abnormalities. Treatment depends on
many specific factors.
For more information on insects and disease, visit
insect_disease.aspx or contact a local arborist certified by the
International Society of Arboriculture. A certified arborist will be
able to provide a professional plant health care evaluation.
The International Society of Arboriculture, headquartered in
Champaign, is a nonprofit organization supporting tree care research
and education around the world. As part of the society's 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 and to find a local ISA-certified
[International Society of
Arboriculture news release]