Monday, January 18, 2016

Fruit Tree Disease Classification

This blog has been primarily about pruning fruit trees. Although pruning is important, it is only one small part of making sure your trees remain healthy and productive. In 2016 we will continue to discuss pruning tips and techniques, but we will also include information about common fruit tree diseases that may affect your trees and the best ways to control them. Before we discuss details, I would like to stand back and look at fruit tree disease from a bird's eye view.

Disease is defined as any condition that affects the normal functions of a living organism. From insects and fungi to improper pruning techniques, fruit tree diseases can be classified as follows:

Insects - Examples include aphids, mites*, thrips, and caterpillars. Insects can be controlled by organic insecticides, traps, and beneficial predatory insects like ladybugs, lace wings, and praying mantis.

Aphids are Classified as Insect Disease
Animals - Animals include deer, raccoons, birds, and squirrels. Most animals are controlled by fences, traps, and nets. There are some sprays on the market that help deter animals, but they are usually temporary solutions and less effective in the long run. Some sprays contain cayenne pepper to attack an animal's taste buds. Other sprays contain blood or predator urine to trigger an animal's fear response.

Deer Can be Considered a Disease
Fungi - Fungi include mildew, rusts, smuts and molds. These are treated with fungicides and copper.

Bacteria- Bacterial diseases include blights that cause wilting, scorching, and cankers. 

Bacteria Can Only be Identified by Symptoms Without a Microscope
Virus - Virus are microscopic organisms that live inside living plant tissues and interrupt a plant's DNA. Unlike most plant diseases viruses cannot be treated and some viruses can cause your entire tree to die which will warrant complete removal.

Mechanical - Mechanical diseases include nails, rope, lawn mowers, and string trimmers. These are just best prevented with common sense.

A Chain Embedded in a Tree Can Interrupt Normal Tree Functions
Environmental - Environmental diseases include snow, hail, flood, wind, etc. and are very difficult to control because they are "acts of God" and not easily anticipated. 

Damage from Heavy Snows Many Permanently Affect Your Trees
Cultural - Cultural diseases usually occur because you, the steward of the garden, did something that negatively effects the tree. Cultural diseases include, planting your tree too deep, over watering or over fertilizing, and improper placement of your tree in the garden. Cultural diseases are best avoided with the proper education.

Doctors have spent centuries studying diseases that infect the human body and still have trouble making the proper diagnosis. Most diseases cannot be identified without costly tests. The same goes with identifying and diagnosing diseases that infect fruit trees. Doctors and horticulturists alike are usually only able to prescribe treatment based on the symptoms of a disease. For example, what is causing the leaves of your tree to shrivel and die? It could be fungal, cultural, or bacterial. For many diseases knowing the exact cause is nearly impossible. For the average home gardener it is only important to understand basic disease classification and the best way to treat each class. If you can tell the difference between insect damage and fungal damage, for example, the hardest part of improving your tree's condition is done. It would do a tree with powdery mildew no good to be sprayed with an insecticide. If you can identify the powdery substance on a leaf as a fungus, then you can treat your tree with a fungicide so that your tree can return to full health and remain productive.

For more information regarding fruit tree care and pruning, follow the links in the right column or email me at

*an insect is a six legged animal, mites are considered arachnids and are more closely related to spiders because they have eight legs. For purposes of fruit tree pest identification mites have been included in the insect classification. 

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