Insect & Disease Problems
Insects and diseases can threaten tree health. As soon as you
notice any abnormality in your tree's appearance, you should begin
a careful examination of the problem. By identifying the specific
symptoms of damage and understanding their causes, you may be
able to diagnose the problem and select an appropriate treatment.
Three things are required for a disease to develop:
1. The presence of a pathogen (the disease-causing agent)
2. Plant susceptibility to that particular pathogen
3. An environment suitable for disease development
Plants vary in susceptibility to pathogens. Many disease-prevention
programs focus on the use of pathogen-resistant plant varieties.
Even if the pathogen is present and a susceptible plant host is
available, the proper environmental conditions must be present
over the correct period of time for the pathogen to infect the
Diseases can be classified into two broad categories: those caused
by infectious or living agents (diseases) and those caused by
noninfectious or nonliving agents (disorders). Examples of infectious
agents include fungi, viruses, and bacteria. Noninfectious diseases,
which account for 70 to 90 percent of all plant problems in urban
areas, can be caused by such factors as nutrient deficiencies,
temperature extremes, vandalism, pollutants, and fluctuations
in moisture. Noninfectious disorders often produce symptoms similar
to those caused by infectious diseases; therefore, it is essential
to distinguish between the two in order to give proper treatment.
Some insects can cause injury and damage to trees and shrubs.
By defoliating trees or sucking their sap, insects can retard
plant growth. By boring into the trunk and branches, they interfere
with sap flow and weaken the tree structure. Insects may also
carry some plant diseases. In many cases, however, the insect
problem is secondary to problems brought on by a stress disorder
or pathogen. It is important to remember that most insects are
beneficial rather than destructive. They help with pollination
or act as predators of more harmful species. Therefore, killing
all insects without regard to their kind and function can actually
be detrimental to tree health. Insects may be divided into three
categories according to their method of feeding: chewing, sucking,
and boring. Insects from each group have characteristic patterns
of damage that will help you determine the culprit and the proper
treatment. Always consult a tree care expert if you have any doubt
about the nature of the insect problem or the proper treatment.
Chewing insects eat plant tissue such as leaves, flowers, buds,
and twigs. Indications of damage by these insects are often seen
by uneven or broken margins on the leaves, skeletonization of
the leaves, and leaf mining. Chewing insects can be beetle adults
or larvae, moth larvae (caterpillars), and many other groups of
insects. The damage they cause (leaf notching, leaf mining,
leaf skeletonizing, etc.) will help in identifying the pest insect.
Sucking insects insert their beak (proboscis) into the tissues
of leaves, twigs, branches, flowers, or fruit and then feed on
the plant’s juices. Some examples of sucking insects are
aphids, mealybugs, thrips, and leafhoppers.Damage caused by these
pests is often indicated by discoloration, drooping, wilting,
leaf spots (stippling), honeydew, or general lack of vigor in
the affected plant.
Boring insects. All pests in this category spend time feeding
somewhere beneath the bark of a tree as larvae. Some borers kill
twigs and leaders when adults feed or when eggs hatch into larvae
that bore into the stem and develop into adults. Other borers,
known as bark beetles, mate at or near the bark surface, and adults
lay eggs in tunnels beneath the bark.
The treatment method used for a particular insect or disease
problem will depend on the species involved, the extent of the
problem, and a variety of other factors specific to the situation
and local regulations. Always consult a professional if you have
any doubt about the nature of the problem or proper treatment.