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TREE DEFENSES(Dorsey, Steve. Natural Tree Care: The Homeowners Complete Guide)

There are worms, bugs, spiders and flying insects on my trees. The leaves look bad and are being eaten and dying. Some of the tree is rotten and diseased. WHAT SHOULD I DO? There are supposed to be bugs and rotten wood on and in trees, insects live there and feed there; and rot and decay is a necessary part of the growth process.

If you look closely enough, you will always find bugs and disease and rot. You can even find them inside of trees and around their roots. The existence of insects and disease is normal. Insects and diseases feed on trees, they live on trees and they live in trees, they need trees and coexist with them. Humans need trees, feed on them, get housing material from them, derive pleasure from them, and successfully coexist with them. This symbiosis which insects and disease have with trees has been going on for millions of years. Trees and insects and disease are still here and thriving, it must be working. Trees produce extra growth to allow for the losses insects and disease inevitably cause. The proper question is, are they causing harm? This is my focus because, if they are not harming your tree, you are fighting insects and disease for your purposes—not to preserve the health of the tree. Try to avoid harming your tree while you are doing it. Before assessing damage, or whether it is significant, be aware of tools the tree itself has and uses, to manage damage which is occurring daily in its constant battle for survival among thousands of other living organisms in the environment.

What defenses does a tree have against insect and disease damage? Did you even consider trees defending themselves by a variety of strategies against insects and disease? Remember, insects, disease and trees have coexisted for millions of years. Natural selection of trees has been going on the entire time producing a balance where trees and insects and disease all successfully survive; or one or the other ceases to be around. The natural selection process among trees, insects and disease is a robust one. For example, where land is cleared by fire or flood, many trees begin to grow. The number of these small seedlings per acre may be 2000 trees. When this acre of trees in 40 or 300 years becomes a mature forest, the number of mature trees will be close to 20. Simple math tells you that 99% of the trees failed to reach maturity. This is far more rigorous than the natural selection process among humans. It explains something many people with wooded lots do not understand. As their trees grow larger, some of them die. These are the weaker ones, the ones that lost the competition with surrounding trees for root space and, in particular, a place in the sun, a perfectly natural and normal process. Before actually dying they decline and often look like they may have an insect or disease problem. The homeowner wishes to help the trees to live. Helping is pointless in this situation, a waste of money and effort. Your tree is dying naturally, let it go, your remaining trees will be stronger with it gone (you really can’t do anything anyway which wouldn’t adversely affect your other trees). The remaining trees were better able to survive any changes or threats happening in their environment. Imagine the environment changing to a dryer one, with more fires. The trees surviving may be the ones with thicker, more fire-resistant bark. The natural selection process of disease and insects is equally rigorous.

Various parts of a tree have their own strategies against insect and disease damage: Leaves are the primary defense line of trees. Spruce tree needles are not eaten much by any animal or insect, meaning they are poisonous, but there is nothing currently in the environment of spruce trees wanting to eat them. Why would they expend the energy producing poison for leaves if nothing around wants to eat them? People who study these things speculate some species of dinosaurs fed on spruce trees, and they ended up surviving by making their needles less edible, or I should say, spruces with needles tasting bad stayed alive to reproduce. They keep making poison because continuing a successful strategy is much easier than changing, and is usually correct.

Poison ivy is poisonous to survive better. It uses some of its energies to make poisons instead of more leaves, what good is making more leaves if most of the leaves are going to be eaten? When gypsy moth larvae eat many of the initial leaves of an oak, the tree activates reserve buds which become new leaves so the tree can survive. However, these new leaves are of a different composition from the first leaves. They have more tannins and are not as moist, becoming less edible to gypsy moth larvae still around or emerging late. Also, when leaves are eaten they emit chemicals, odors detected by nearby trees with specialized cells, which respond by activating their own defenses, changing the composition of their leaves before the insects start eating them. You might compare it to Paul Revere with extreme body odor. He only needs to get close to a town to deliver everyone the message, “the British (insects) are coming”, more efficiently than Paul actually did. Leaves may delay their emergence where insect pests are present, mitigating damage. Existing leaves disconnect after their sugars and recyclable materials withdraw back into the tree, and detach early to avoid expected damage. These are some of the ways we know leaves defend against insect damage.

Surely there are many more we are not yet aware of. Tree sap and other fluids produced are primary defensive tools. Sap can flush away an insect or drown it. Most needle bearing trees contain reservoirs of resin in addition to regular sap. It is often used to deter and trap invading insects and disease spores, and can contain poisonous substances discouraging, even killing insect and disease invaders. Cherry trees produce an amber-like gummy substance which physically blocks insects, often encapsulating them. Roots of Black Walnuts exude a chemical which acts as an herbicide to kill off competing plants. Root space is critical, and Black Walnut trees are notorious for this, many kinds of plants often mysteriously perish where Black Walnut roots are nearby. They produce a substance called juglone which is toxic to many plants. Trees survive better if there is less competition for sunlight and root space and water and nutrients.

Information used education propose from:

Dorsey, Steve. Natural Tree Care: The Homeowners Complete Guide . Dorseys Tree Service. Kindle Edition.

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