Though it may look like a growth or fungus, sometimes bumps found on the trunk, twigs, or leaves of your plants are more than first meets the eye. The bumps may actually be tree scale–a type of small insect that feeds on sap. They are indiscriminate in choosing their targets, feeding on a wide range of trees and smaller plants including fruit trees and ornamental shrubs. There are over 1,000 species of scale on this continent; some species can cause significant injury to the trunk or leaves, while others are more benign and rarely harm their host. Luckily, few infestations are completely lethal to a plant if you can identify and properly address the pests.
While there are many different species, there are two main types of scale. Soft scales, as the name implies, have a soft exoskeleton. Instead of a hard shell, they secrete a waxy, almost cottony substance that protects their small bodies (generally from one-eighth to one-half of an inch in diameter) from the elements. Their bodies are domed, creating small bumps on the plants they infest. “Honeydew”, a sticky, sugary substance, is produced as they drink the plants’ sap.
Armored scales, on the other hand, have a hard shield-like covering that is created as they shed skin. Like actual armor, this layer is not attached to their body but carried for protection. They’re flat and spherical, but generally smaller than soft scales. Armored scales do not produce any “honeydew” as they drink sap like soft scales do.
How to Identify Tree Scale
If you see small bumps on the branches, trunks, twigs, and leaves, of your plants, that’s a sure sign of scale. However, to confirm that it’s scale, keep an eye out for some of these other signs:
- Watch to see if your plants’ leaves are dying off or changing colors to yellow and brown
- Slowed growth in your plant during its growing season
- “Honeydew” present on the plant or in the area around/underneath the infected tree, such as on the ground or on outdoor furniture and decorations.
What Can You Do?
You have a few options if you find scale on your plants. First, check all your trees and shrubs and figure out which ones are infested. This will help determine the amount of treatment needed.
If you have relatively few scale-ridden plants, releasing predatory insects into your yard like ladybugs is an effective method of pest control. Ladybugs love to feed on scale, and while they won’t eliminate the entire population, they’ll keep it to a manageable size. If the infestation is extremely small, such as limited to one or two houseplants, you can even remove the scale by hand.
For wider-reaching infestations, it’s much more important to stop the scale immediately. Unfortunately, scales are not widely affected by most pesticides–their protective coatings keep the chemicals from harming them. If you choose to use a spray pesticide, it’s best to apply the treatment during summer when the baby scales are active and have not yet formed their protective coatings. Systemic insecticides that you inject into the tree are quite effective, since they enter the sap and are ingested by the insects. Horticultural oils will coat the scale and make it difficult for them to breathe, and make the uninfested plants uninhabitable.