Identifying Diseases and Pests of Forest Treestuscolaagriculture.weebly.com/uploads/8/3/8/9/8389114/...Because this type of pest feeds on leaves, it is known as a defoliator. (Courtesy,

Identifying Diseases and Pestsof Forest Trees

CALLING a tree a “mighty oak” or a “majestic

redwood” may give the impression that the tree

is indestructible. Yet, like any other organism, a tree

can suffer from pests and diseases. In time, pests

and disease result in decline and die. This unit

discusses some of the major pests and diseases of

forest trees.

Objective:

� Describe major pests and diseases of for-

est trees in addition to pest and disease

management.

Key Terms:

�

Forest Trees: Problems and Solutions

A number of insect pests and diseases affect forest trees. The damage they cause leads to the

decline and death of trees. Collectively, the damages inflicted on forest trees cost the forest

industry millions of dollars.

INSECT PESTS OF FOREST TREES

Insects are pests that attack forest trees. Some insects are pests to all kinds of trees, but oth-

ers only affect certain species. Insects can cause damage to trees in a variety of ways.

E-unit: Identifying Diseases and Pests of Forest Trees

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bark borers

biological controls

chemical controls

defoliators

management controls

parasites

pathogen

root feeders

sap suckers

tip feeders

wood borers

Bark Borers

As the name suggests, bark borers are insects

that attack trees by tunneling underneath the bark.

The soft cambium and newly produced wood and

bark cells are destroyed. This effectively girdles the

tree, cutting off the supply of nutrients. In addition,

the damage often provides an entry point for diseases

and other pests to attack the tree. One of the most

common insects of this type is the Southern Pine

Bark Beetle.

Defoliators

Defoliators are insects that cause tree damage by

feeding on the leaves or needles. In most cases, the

insect larvae—not the adults—do the damage.

Wood Borers

Wood borers eat their way

through the tree sapwood and heart-

wood. This damage causes the wood to

weaken. The most well-known insect

in this category is the termite.

Tip Feeders

Insects that attack young twigs,

stems, or buds are tip feeders. These insects attack the most tender parts of the tree.

Sap Suckers

Sap suckers are insects equipped with penetrating mouthparts, allowing them to feed on

tree sap. These insects rarely cause the tree to die. However, trees are weakened and growth

slows. Aphids and scales are common examples of sap suckers.

Root Feeders

Root feeders are insects in the soil around the tree that feed on the tree’s roots. These

insects (e.g., white grubs and wireworms) cause the most damage to tree seedlings.




FIGURE 1. Due to attacks from borers, these trees

have died.

FIGURE 2. Because this type of pest feeds on leaves, it is known as a

defoliator. (Courtesy, U.S. Fish and Wildlife Service)

DISEASE PROBLEMS OF

FOREST TREES

Most diseases are caused by para-

sites—organisms that rely on other

organisms for their food. Parasite organ-

isms can be classified into five major cate-

gories: fungi, bacteria, nematodes, viruses,

and mistletoes.

Of the five major categories of parasite

organisms, fungi cause the most damage

because they spread by tiny spores and can

multiply very quickly. These diseases can

attack any part of the tree. Stem diseases

are generally considered the most danger-

ous because they are more likely to cause

tree death. In contrast, leaf and root dis-

eases generally do not kill the tree. Instead,

they weaken the plant and slow its growth.

Examples of stem diseases are Dutch elm

disease, chestnut blight, fusiform rust, and

various types of heart rot.

INSECT AND DISEASE

MANAGEMENT

The key to a healthy forest is good forest manage-

ment. A forest manager has several alternatives from

which to choose regarding the control of insect and dis-

ease pests. Three basic control types are biological,

chemical, and management.

Biological Controls

Natural controls for most insect pests exist in nature.

However, these natural controls are slow. Whenever

foresters alter these natural controls to manage insect

pests, the controls become biological controls. For

example, every insect has a natural enemy. An example

of a biological control would be the introduction of an

insect pest predator into the infected area or the intro-

duction of a pathogen. A pathogen is any disease-caus-




FIGURE 3. This leaf indicates that the tree has been infected by a

parasite.

FIGURE 4. Mistletoe has covered this tree.

FIGURE 5. The phorid fly is now used as a

biological control against fire ants. (Courtesy,

Agricultural Research Service, USDA)

ing organism. The pathogen that attacks the specific insect pest may be available and can be

introduced into the insect population.

Chemical Controls

Chemical controls involve pesticides. The use of pesticides on forest trees is regulated by

the Environmental Protection Agency (EPA). Pesticides offer a quick and effective short-term

solution to insect pests; however, other control measures often need to be used for long-term

forest management.

Management Controls

Management controls consist of various management practices that the forester can

employ, including the removal of infested trees and tree parts, the use of insect-resistant tree

varieties, the maintenance of proper tree populations, and prescribed burns.

The most effective control of forest disease is good management by the forester. Many dis-

eases can be prevented from entering a forest by dusting the stumps of cut trees with borax or

creosote. By removing damaged trees from the forest, the likelihood of disease infestation is

reduced. In most cases, once a tree becomes diseased, little can be done. Therefore, prevention

is the answer to a healthy forest.

Summary:

� There are a number of insect pests and diseases of forest trees. The damage theycause leads to the decline and death of trees. Collectively, the damages inflicted costthe forest industry millions of dollars.

Insects can cause damage to trees in a variety of ways. Common insect pests arebark borers, defoliators, wood borers, tip feeders, sap suckers, and root feeders.

Most diseases are caused by parasites that can be classified into five major categories:fungi, bacteria, nematodes, viruses, and mistletoes. Of the five major categories ofparasite organisms, fungi cause the most damage.

The key to a healthy forest is good forest management. Three basic control typesfrom which a forest manager can choose are biological, chemical, and management.

Checking Your Knowledge:

� 1. What are the major types of insects that cause damage to forest trees?

2. What are five categories of organisms that cause disease to forest trees?

3. Which type of organism is the major cause of forest tree disease?




4. What are the three insect and disease controls available to a forest manager?

5. What is the most effective way to control insect pests and diseases?

Expanding Your Knowledge:

� Hike through a forest and look for evidence of insect pests and diseases of the foresttrees. If possible, involve a forester, entomologist, or plant pathologist.

Web Links:

� Forest Diseases

http://www.forestencyclopedia.net/p/p1372

Forestry Images

http://www.forestryimages.org/

Forest Pest Control

http://www.bugwood.org/pestcontrol/

Major Tree Insect Pests

http://forestry.about.com/blsectex.htm

Most Damaging Forest Diseases

http://forestry.about.com/od/forestdiseases/Most_Damaging_Forest_Diseases.htm




http://www.forestencyclopedia.net/p/p1372

http://www.forestryimages.org/

http://www.bugwood.org/pestcontrol/

http://forestry.about.com/blsectex.htm

http://forestry.about.com/od/forestdiseases/Most_Damaging_Forest_Diseases.htm

Documents

Identifying Diseases and Pests of Forest Treestuscolaagriculture.weebly.com/uploads/8/3/8/9/8389114/...Because this type of pest feeds on leaves, it is known as a defoliator. (Courtesy,