Preventing Scale Insects Inside and Outside
Scale insects and mealybugs are tiny, sap-sucking pests that can spread rapidly. You may have seen scale insects on leaves and stems but never noticed them! Inconspicuous, well-camouflaged, and small, they don’t attract much attention, but they can be a significant pest. Here’s how to get rid of scale and mealybugs on your plants!
What are Scale Insects?
Scale insects are tiny bugs that vary widely in appearance and look more like a blemish on a plant’s foliage than an insect. The adult females are immobile, and the nymphs, called crawlers, don’t move far from where they hatched. Only the males are genuinely mobile, flying around to find a mate.
Although highly variable, scale insects share one common characteristic: They are covered or protected by a waxy substance that looks much like the scales on a fish. This protective covering makes them more resistant to standard chemical control methods.
Scale insects have piercing-sucking mouthparts that are used to feed on the sap of plants. While a few scale insects won’t cause much harm, infestations can significantly weaken a tree or plant, making it susceptible to other pests, diseases, and stresses.
Some scale insects create a sticky substance called honeydew, which can cause the growth of black sooty mold on the leaves and block the sunlight needed for photosynthesis.
Scale insects are divided into two main categories: soft-scaled and armored.
Soft Scales
More common on indoor plants, soft scale insects often inhabit the underside of leaves or stems. After hatching, nymphs will crawl to a new location where they will settle down for the rest of their lives.
Mealybugs are one type of soft-scaled scale insect. They secrete a powdery, waxy coating that is often white or light colored. They may have a hairy or cottony appearance as well.
Younger scale insects are typically lighter in color and darken as they mature. Outdoors, the honeydew they create can make a sticky mess on the ground under heavily infested trees.
Armored Scales
The smaller armored scales have a more rigid, waxy shell-like covering. They may be hard to spot if their color closely matches the plant.
Hard scales can cause more damage to their host than soft scales and may even form a thick crust of insects that feed heavily on the plant. They do not create honeydew like soft-scale insects and typically infest trees and shrubs.
Check out this overview of scale insects by Iowa State University Extension and this pamphlet from the University of California IPM program for more information.
Andy Wilcox
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Have you ever heard of them infesting humans? If so how would you get rid of them.
Hi, Vance. Scale insects are not a threat to humans. They live on the sap they suck from plants, so your sap-less skin is of no interest to them. If the insects are in your house, they probably took up residence on houseplants. They need to be picked off of houseplants and then the houseplants should be treated with an insecticide such as neem oil.
How bad of an infestation is too bad? I live in Zone 4b in Wyoming. I have several aspens in my yard, and 3 have scale surrounding their trunks and continuing upward about 5-8 feet or so. Some lower leaves have some stickiness and blackish mold, just as described here in your article. The local tree service says that chemicals are the only treatment, and that it has be done yearly for the life of the tree, and may not yield results even then. As there's been no noticeable decrease in the scale over the last 5 years of treatments since we moved into this house, I'm no longer convinced that this is likely to yield positive results. Would you suggest trying some of the suggestions you've made in this article, or do you think they're too far gone? If you think they're too far gone, how likely do you think it would be for the male scale insects to travel to the other aspens nearby? Might they be more likely to travel during certain times of the year than others? Thanks!
Hi, Kerry,
We’re sorry that your aspens are having trouble with scale. If the treatments from the tree service are not yielding results, then you might try contacting your county’s Cooperative Extension service. They might know of some other things that you might try.
https://www.uwyo.edu/uwe/
In addition, you can also try some of the controls mentioned in our article. It might first help, though, to identify what kind of scale is attacking your aspens. There are soft and armored types of scales, and treatment/timing can vary a bit depending on the type you have. The article below might also help, as it addresses some scales that attack aspen, but in Colorado:
https://extension.colostate.edu/topic-areas/insects/oystershell-scale-5-513/
One article from the Wyoming extension says that oystershell scale (an armored scale type) is a common pest of aspens in your state. For this scale, they usually hatch in early to mid June in your area. Treatment at this stage (crawlers) is important, before their protective coating is formed; often with a repeat treatment in 10 to 14 days. Also prune out infested branches if feasible.
If you have oystershell scale, the crawlers might move to other trees, carried by wind or animals. That is the only stage at which the pest is mobile; they are mobile for just a few days, but some might hatch a bit later than others. In some states, males are not produced.
Here is an article from the Utah Extension about oystershell scale:
https://extension.usu.edu/pests/research/oyster-shell-scale
Over years, a tree with a heavy infestation may decline and die. Monitor the health of your trees—check for branch dieback, yellow/wilted leaves, etc. To aid your trees, alleviate stress and make sure that they have good soil and nutrients and enough water.
Hope this helps!
