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Pest of the Month: Scale Insects

Pest of the Month: Scale Insects

This month we are discussing a pest that can really do some damage to your trees, scale insects.

In addition to discussing what they are and how they hurt your trees, we will also be giving you our top tips for removing them and fixing the damage they do. First, let’s talk about what scale insects are and how they look.

What Are Scale Insects?

Gilles San Martin from Namur, Belgium

Scale insects are very small, and there are around 8,000 different species of them. They are of the order Hemiptera , and suborder Sternorrhyncha .

They can vary quite a bit when it comes to their appearance. Some are extremely small (between 1-2 mm) and grow under wax covers. These species can be shaped like oyster or mussel shells. Other species grow to be about 5 mm and have a shiny, pearl-like appearance covered in wax. It really depends on the specific type of scale insect you are dealing with.

The adult female scales are typically immobile, and they stay permanently attached to the plant they have parasitized. For defense, they secrete a waxy coating to disguise them as reptiles or fish scales (hence the name scale insect).

Adult male scale insects usually have wings (depending on the species), and only last a day or two. The species that do have wings will typically have one pair of functional wings and then forewings.

Finding and Identifying Scale Insects

These insects typically thrive in dry, warm environments. The bugs are very small, flat, and are usually an oval shape with a protective shell that is beige to brown.

You can find these insects on the undersides of leaves, or around leaf joints.

Scale insects are usually one of three different types. There are mealybug scales , armored scale, and soft scale insects. The armored and soft scale insects are the ones that will cause the most damage, so you want to especially keep an eye out for those.

The Scale Insect Life Cycle

The adult female scale insects will lay eggs underneath their protective covering, and they will hatch over 1-3 weeks. These newly-hatched insects (known as crawlers), will migrate from this cover and move around until they find a good place on the tree to feed.

At this point, the crawlers will begin to feed and start to grow their own armor as they become adult scale insects. They won’t pupate, and there may be several overlapping generations that appear per year.

How do Scale Insects Damage Trees?


Now that you know what they look like and where to find scale insects, let’s talk about the damage they can actually cause to your trees.

These insects feed by sucking the sap out of trees and shrubs through their mouths. Feeding sessions will actually cause the leaves of the plant in question to yellow and/or wilt, the appearance to suffer, and even the death of the part being eaten from or the whole plant.

Once the tree is weakened from the sap-sucking, it may start to lose vigor and become more open to injuries from cold temperatures, other pests, infections from diseases, and/or drought.

During their feeding, the soft scale insects excrete honeydew , which is extremely sticky and sweet. It is a mixture of undigested water and sugar that passes through the bug’s digestive system and placed onto the stems and leaves of the tree. The secretion will make the plant look wet and shiny, and actually attracts other insects to it.

Honeydew may also encourage sooty mold to grow, giving the plant a dark, dirty appearance. If the tree or plant in question is near your home, sidewalk or cars, the honeydew could cause damage to them as well.

How to Control Scale Insects

Katja Schulz from Washington DC USA

So what can you do to control scale insects and save your trees? Here are some of our top tips.

1. When you notice infected leaves, twigs, and branches on your trees and plants, dispose of them immediately. Cut them away from your healthy trees and either throw them out or burn them.

2. If you notice a branch or leaves that only have a few scale insects on them, consider removing them by hand and allowing that part of the tree to stay intact. When doing this, make sure that you wear gloves.

For those of you that don’t want to touch the bugs with your hands, you can also use a cotton swab or other material to dab the pests with alcohol to kill and remove them.

3. You can use organic pesticides to remove larger quantities of scale insects, just keep in mind that you will have to apply them several times for consistent results. Horticultural oils will also work for all of the pest’s life stages.

4. Lastly, you can use insects that are commercially available like lacewing and ladybugs to kill scale insects in their “crawler” stage.

Our Final Thoughts on Scale Insects

No matter what amount of scale insects you have hurting your trees and other plants, they need to be dealt with as soon as possible.

If you are in the San Francisco Bay Area and need additional assistance with removing these pests, contact Arborist Now for help.

Title Image: Katja Schulz from Washington DC USA

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