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STUDY 2. TREE DISEASES

Because trees have wants analogous to those of human beings, they also have diseases similar to those which afflict human beings. In many cases these diseases act like cancerous growths upon the human body; in some instances, the ailment may be a general failing due to improper feeding, and in other cases it may be due to interference with the life processes of the tree.
Cancerous Tree Growth


HOW TO TELL AN AILING TREE

Whatever the cause, an ailing tree will manifest its ailment by one or more symptoms.

A change of color in the leaves at a time when they should be perfectly green indicates that the tree is not growing under normal conditions, possibly because of an insufficiency of moisture or light or an overdose of foreign gases or salts. Withering of the leaves is another sign of irregularity in water supply. Dead tops point to some difficulty in the soil conditions or to some disease of the roots or branches. Spotted leaves and mushroom-like growths or brackets protruding from the bark are sure signs of disease.
Spots Signify Disease
In attempting to find out whether a tree is healthy or not, one would therefore do well to consider whether the conditions under which it is growing are normal or not; whether the tree is suitable for the location; whether the soil is too dry or too wet; whether the roots are deprived of their necessary water and air by an impenetrable cover of concrete or soil; whether the soil is well drained and free from foreign gases and salts; whether the tree is receiving plenty of light or is too much exposed; and whether it is free from insects and fungi.
Diseased Oak Leaf
If, after a thorough examination, it is found that the ailment has gone too far, it may not be wise to try to save the tree. A timely removal of a tree badly infested with insects or fungi may often be the best procedure and may save many neighboring trees from contagious infection. For this, however, no rules can be laid down and much will depend on the local conditions and the judgment and knowledge of the person concerned.
Diseased Fruit


FUNGI AS FACTORS OF DISEASE

The trees, the shrubs and the flowers with which we are familiar are rooted in the ground and derive their food both from the soil and from the air. There is, however, another group of plants,—the fungi,—the roots of which grow in trees and other plants and which obtain their food entirely from the trees or plants upon which they grow. The fungi cannot manufacture their own food as other plants do and consequently absorb the food of their host, eventually reducing it to dust. The fungi are thus disease-producing factors and the source of most of the diseases of trees.
Fungus Growth
When we can see fungi growing on a tree, we may safely assume that they are already in an advanced state of development. We generally discover their presence when their fruiting bodies appear on the surface of the tree. These fruiting bodies are the familiar mushrooms, puffballs, toadstools or shelf-like brackets that one often sees on trees. In some cases, they spread over the surface of the wood in thin patches. They vary in size from large bodies to mere pustules barely visible to the naked eye. Their variation in color is also significant, ranging from colorless to black and red but never green. They often emulate the color of the bark.
Tree Fungus
Radiating from these fruiting bodies into the tissues of the tree are a large number of minute fibers, comprising the mycelium of the fungus. These fibers penetrate the body of the tree in all directions and absorb its food. The mycelium is the most important part of the fungus growth. If the fruiting body is removed, another soon takes its place, but if the entire mycelium is cut out, the fungus will never come back. The fruiting body of the fungus bears the seed or spores. These spores are carried by the wind or insects to other trees where they take root in some wound or crevice of the bark and start a new infestation.
White Threads of Mycelium
The infestation will be favored in its growth if the spore can find plenty of food, water, warmth and darkness. As these conditions generally exist in wounds and cavities of trees, it is wise to keep all wounds well covered with coal tar and to so drain the cavities that moisture cannot lodge in them. This subject will be gone into more fully in the following two studies on "Pruning Trees" and "Tree Repair."

While the majority of the fungi grow on the trunks and limbs of trees, some attack the leaves, some the twigs and others the roots. Some fungi grow on living wood some on dead wood and some on both. Those that attack the living trees are the most dangerous from the standpoint of disease.

THE CHESTNUT DISEASE

The disease which is threatening the destruction of all the chestnut trees in America is a fungus which has, within recent years, assumed such vast proportions that it deserves special comment. The fungus is known as Diaporthe parasitica (Murrill), and was first observed in the vicinity of New York in 1905. At that time, only a few trees were known to have been killed by this disease, but now the disease has advanced over the whole chestnut area in the United States, reaching as far south as Virginia and as far west as Buffalo.
Chestnut Blight Splits the Bark
The fungus attacks the cambium tissue underneath the bark. It enters through a wound in the bark and sends its fungous threads from the point of infection all around the trunk until the latter is girdled and killed. This may all happen within one season. It is not until the tree has practically been destroyed that the disease makes its appearance on the surface of the bark in the form of brown patches studded with little pustules that carry the spores. When once girdled, the tree is killed above the point of infection and everything above dies, while some of the twigs below may live until they are attacked individually by the disease or until the trunk below their origin is infected.

All species of chestnut trees are subject to the disease. The Japanese and Spanish varieties appear to be highly resistant, but are not immune. Other species of trees besides chestnuts are not subject to the disease.

There is no remedy or preventive for this disease. From the nature of its attack, which is on the inner layer of the tree, it is evident that all applications of fungicides, which must necessarily be applied to the outside of the tree, will not reach the disease. Injections are impossible and other suggested remedies, such as boring holes in the wood for the purpose of inserting chemicals, are futile.

The wood of the chestnut tree, within three or four years after its death, is still sound and may be used for telephone and telegraph poles, posts, railroad ties, lumber and firewood.

Directions

Study the lesson for one week.

Over the week:

  • Read the lesson.
  • Review the synopsis.
  • Recite aloud the vocabulary words and their definitions.
  • Learn the concepts.
  • Complete the enrichment activities.
  • Study the review questions.

Synopsis

This lesson looks at signs of ailing trees as well as several diseases that have devastated tree populations. In the lush times of late spring and summer, ailing trees may be detected by withered, spotted, or discolored leaves, including when the top leaves are dead. Throughout the year, mushroom-like growths or brackets protruding from the bark are sure signs of disease.

Vocabulary

Fungus: Any member of the kingdom Fungi, having no chlorophyll. Fungi may be unicellular (single-celled organism) or multicellular (multiple-celled organism).
Spore: A reproductive particle, usually a single cell, released by a fungus, alga, or plant that may germinate into another.
Fruiting Body: The structure on a fungus which houses the spore-producing organs.
Mycelium: The vegetative part of any fungus, consisting of a mass of branching, threadlike hyphae, often underground.
Mushroom: Any of the fleshy fruiting bodies of fungi typically produced above ground on soil or on their food sources.
Puffball: Any of various fungi that produce a cloud of brown dust-like spores from their mature fruiting bodies.
Toadstool: Any inedible or poisonous mushroom.
Parasite: An organism that lives on or in another organism of a different species, deriving benefit from living on or in that other organism, while not contributing towards that other organism sufficiently to cover the cost to that other organism.
Decomposer: Any organism that feeds off decomposing organic material, especially bacterium or fungi.

Concepts

WHAT ARE FUNGI?

  1. Why did the Fungi leave the party? There wasn't mushroom.
  2. Why did the Fungi get an invitation to the party? Because he's a Fungi (fun guy)!
  3. Fungi (singular fungus) include mushrooms, yeasts, and molds.

FUNGI VS. PLANTS

  1. Fungi are not plants - they are in the same domain but have their own kingdom.
  2. Find the kingdoms Plantae and Fungi on the tree of life.
  3. What do the kingdoms Plantae and Fungi share in common?
  4. Fungi do not contain chlorophyll.
  5. Fungi do not engage in photosynthesis.
  6. In fact, fungi are more closely related to animals than to plants.

FUNGI GROWTH

If fungi do not engage in photosynthesis like plants and do not have mouths to eat like animals, how do they obtain nutrients and grow?

  1. Fungi excrete substances that digest and decompose other matter.
  2. Some fungi are parasites that feed on living plants and animals.
  3. Other fungi are decomposers that feed on dead plants and animals.

HARMFUL FUNGI

  1. Yeast lives on human skin and intestines.
  2. Yeast overgrowth can cause diaper rash in babies and other infections.

HELPFUL FUNGI

However, fungi have many beneficial uses for humans as well.

  1. Mushrooms provide a food source for humans.
  2. Yeast is used in bread making and beer brewing.
  3. Some molds, such as penicillin (e.g. amoxicillin pills), are made into medicine to kill bacteria and cure human diseases.

EXAMPLE FUNGI

  1. Puffballs
  2. Bracket Fungi
  3. Mold Growing on Bread
  4. Mold Growing on an Orange
  5. Mushrooms
  6. Rapid Rise Yeast Used to Bake Bread

Enrichment

Activity 1: Narrate the Lesson

  • After reading or listening to the lesson, narrate the lesson aloud using your own words.

Activity 2: Study the Lesson Pictures

  • Study the lesson pictures and describe how they relate to the lesson.

Activity 3: Identify Taxonomic Classifications

Study the classification diagram of the edible and prized fungi, the black morel, to answer the questions.

  • What is the order of Morchella esculenta?
  • What is the species (two-part name) of Morchella esculenta?
  • What is the domain of Morchella esculenta?
  • What is the genus of Morchella esculenta?
  • What is the family of Morchella esculenta?
  • What is the phylum of Morchella esculenta?
  • What is the kingdom of Morchella esculenta?
  • What is the class of Morchella esculenta?
  • What is the binomial name of the black morel?
  • What is the common name of Morchella esculenta?

Activity 4: Take a Nature Walk

  • Bring a small sketchbook and embark on a nature walk.
  • Find trees damaged by disease such as fungi growths or brackets protruding from the bark.
  • Make observations, make sketches, and gather data.
  • Use the gathered information to create the field book entry.

Activity 5: Complete a Field Book Entry   

After your nature walk, complete page 38 in 'Science Field Book for Fourth Grade.'

Review

Question 1

What is the genus of Morchella esculenta?
1 / 7

Answer 1

The genus of Morchella esculenta is Morchella.
1 / 7

Question 2

What is the species (two-part name) of Morchella esculenta?
2 / 7

Answer 2

The species of Morchella esculenta is Morchella esculenta.
2 / 7

Question 3

What is the binomial name of Morchella esculenta?
3 / 7

Answer 3

The binomial name of Morchella esculenta is Morchella esculenta.
3 / 7

Question 4

What is the kingdom of Morchella esculenta?
4 / 7

Answer 4

The kingdom of Morchella esculenta is the fungi kingdom.
4 / 7

Question 5

Are fungi plants? Why or why not?
5 / 7

Answer 5

No, fungi are not plants and have their own kingdom. They do not contain chlorophyll or engage in photosynthesis like plants.
5 / 7

Question 6

List three ways fungi help humans?
6 / 7

Answer 6

Mushrooms provide a food source for humans. Yeast is used in bread making and beer brewing. Some molds can be used to make medicine to kill bacteria.
6 / 7

Question 7

What is one way fungi can hurt humans?
7 / 7

Answer 7

Yeast can cause diaper rash in babies and other infections.
7 / 7

  1. What is the genus of Morchella esculenta? The genus of Morchella esculenta is Morchella.
  2. What is the species (two-part name) of Morchella esculenta? The species of Morchella esculenta is Morchella esculenta.
  3. What is the binomial name of Morchella esculenta? The binomial name of Morchella esculenta is Morchella esculenta.
  4. What is the kingdom of Morchella esculenta? The kingdom of Morchella esculenta is the fungi kingdom.
  5. Are fungi plants? Why or why not? No, fungi are not plants and have their own kingdom. They do not contain chlorophyll or engage in photosynthesis like plants.
  6. List three ways fungi help humans? Mushrooms provide a food source for humans. Yeast is used in bread making and beer brewing. Some molds can be used to make medicine to kill bacteria.
  7. What is one way fungi can hurt humans? Yeast can cause diaper rash in babies and other infections.

References

  1. 'Studies of Trees' by Jacob Joshua Levison. gutenberg.org/ebooks/16116. n.p.
  2. 'Fungi.' Wikipedia. Wikipedia.org. n.p.

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