Plant Diseases: Scales
Scales are unlike other insects that damage plants, because for the majority of their lives, these insects do not move at all. These insects are a common problem among many different types of trees and shrubs, including azaleas, birch trees, juniper trees and magnolia trees. Does this Spark an idea?
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Types of Scales
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Two different types of scales damage plants: armored scales and soft scales. In a single year, there can be many generations of armored scales. Soft scales on the other hand typically have only one generation per year. While they are young, soft scales can crawl around the tree before deciding on a permanent feeding sites. This type of scale is also larger than armored scales. Both types of scales do not move once they attach themselves to the site they have chosen for feeding.
Life Cycle of Scales
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Mother scales produce eggs. These eggs hatch beneath the mother. When the scales first hatch, they have legs, making it possible for them to move around the tree. As the scale grows, it is covered by a waxy substance. Male scales feature wings and move around enough to find a female to mate with.
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Effects of Armored Scales
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Yellowing of leaves and premature leaf drop are common symptoms displayed by trees infected with armored scales. Twig and limb dieback and cracked bark are also symptoms. As the population of armored scales increases on a tree, the damage increases, and in some extreme cases, a tree can be killed by armored scales.
Effects if Soft Scales
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When soft scales infect a tree, the primary symptom is the presence of a substance called "honeydew" covering the fruit and leaves of the tree. Leaves and fruit could also have black mold. Both of these substances attract ants, flies, wasps and bees, but the damage caused by soft scales is not normally severe enough to kill the tree.
Controlling Scales
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Because scales feed heavier on stressed trees, proper watering and fertilizing of shrubs and trees can help prevent scales from feeding on plants. Dormant sprays are also effective in eliminating the presence of scales. Oils and insecticidal soaps have also been proven effective on both types of scales. Because there can be multiple generations every year, insecticides should be applied to the tree or bush on a number of occasions. After application, check the scales to see if they are alive or dead. Dead scales will be hollow and will easily flake off the surface of the tree.
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