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Tree Diseases

What is Tree Scale, and what can homeowners do about it?

By: Lacey Russell, PhD | June 6th, 2018

You may not have noticed these bizarre little insects on your trees or shrubs until you notice the yellowing leaves or stunted growth…something about your tree just doesn't look right. You flip over a leaf or inspect a twig and fing dozens of little bumps camped out on your plant. These immobile little bumps belong to a group of insects called scale insects and they are a problem!

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Often times scale go unnoticed until the tree begins to decline. They spend most of their lives in one place, not moving around so they’re easy to overlook.

A scale insect damages a plant by sucking out the juice. Tree scale, one of many tree conditions, causes reduced vigor or strength in your tree and can be unsightly. They can also introduce disease pathogens and severely weaken a tree if the problem is not taken care of. Unfortunately, these scale bugs are hard to get rid of because many of them produce a protective armor under which they live.

See images of tree scale here.

Types of Tree Scale insects

Soft Scales

Calico, kermes, lecanium, tortoise, and wax scales.

These are large scales (up to 3/8 of an inch), they have greatly mottled patterns of light to dark brown and appear as raised bumps on leaves and twigs. Most species produce a lot of honeydew, and sooty mold is common when the weather is humid. These soft scale infestations can cause leaves to yellow, die and fall off prematurely, and limbs and entire plants to die. Host plants include oaks, conifers, elms, redbud, pyracantha, hollies, euonymus, camellia, citrus, and many houseplants.

Pit Scales

These are small round scales and are found in the centers of depressed areas of pits on the leaves and stems. They are most often found on sweetgum, Pittosporum, mock orange, ligustrum, ilex, and Texas mountain laurel.

Hard or Armored Scales

These scales are small (1/8 inch), oval-shaped, and are generally dark gray to white in color. They infest all parts of the plant and can cause the leaves to turn yellow and fall off and the plant to be less healthy and even die. Hard scales do not produce honeydew. They infest many species of outdoor trees, shrubs, and grasses, and indoor ornamental plants. Some of the more commonly infested plants include oaks, fruit trees, conifers, euonymous, holly, privet, and ferns. Some of these scales include pine needle scale, Florida red scale, euonymous scale and obscure scale.

Mealy Bugs

These insects derive their name from the whitish, waxy or mealy appearance of the wax they secrete. These waxy secretions in some species project into long strings or filaments, hence the common name “longtail mealybug.”

Mealy bugs can infest all parts of the plant and stunt its growth, discolor and deform the leaves, and eventually kill the plant. Mealybugs also produce honeydew, which can cause sooty mold to appear.

It's important to know what kind of scale insects you have. It will determine the kind of treatment you use. Soft scales are a good target for beneficial insects such as ladybugs and wasps. Spraying a conventional pesticide will kill the scale’s natural enemies who actually provide the best lasting control in the landscape.

Honeydew

Tree scale insects can make honeydew, which is a nuisance and a threat to plants. Parked cars, sidewalks, and benches under the tree become a sticky mess. The sugar liquid attracts ant, flies, and wasps. The honeydew also becomes particularly ugly when it becomes food for a black fungus called sooty mold. Some ants actually protect soft scale insects and defend them from predators to ensure a production of honeydew. If you notice a large population of ants associated with the honeydew production, action may be required.

Getting Rid of Tree Scale

Scale insects are a bummer and can be hard to get rid of if the infestation gets out of control. It's best to reach out to an arborist specializing in tree and plant health care to to help you free your tree from these tree-killing pests.

Checking regularly under the leaves and on twigs in your landscape will help you stay ahead of a scale problem. If you find any, let you neighbors know, as the problem could be in their trees as well. Good luck!

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