Scale is a common pest to both landscaping and indoor plants. They can sometimes be difficult to identify because they look nonliving.
Oftentimes they mimic various plant parts, such as bark and buds. Other species appear as small, white and can resemble small bits of cotton on leaves and stems.
Asian Bark Scale is a relatively new species and was first found in the U.S. in 2014 in Plano, TX
There are two types of scale insects. As scale insects mature, many species exude wax from pores on their bodies. This wax generally forms a protective covering that may or may not be attached to their body.
They are often known as soft-bodied scales. Scale insects with hardened wax coverings that detach easily from their soft bodies underneath are referred to as “hard” or “armored” scales.
Scale insects feed on the sap of the tree. The insects insert their mouthparts into plant tissues and suck out the nutrients.
If the infestation becomes severe, the plant or tree’s growth may be stunted; its leaves may develop yellow blotches; the branches may die, and some or all of the leaves may fall off.
After feeding, scale excretes a sugary, sticky liquid referred to as “honeydew.” The honeydew can accumulate on the stems and leaves, making them appear shiny and the sugary liquid often attracts other insects like ants.
In humid areas, a fungus can grow on the honeydew. The fungus turns the honeydew black and makes the plant leaves and stems appear sooty, it is commonly known as “sooty mold”.
Many homeowners may choose to wash the sooty mold off of their plants. It’s unsightly and unwanted. You can wash the sooty mold off of the leaves and bark with a mixture of water and dish soap!
All species of scale has two life stages in common: a mobile stage, which is generally followed by a motion-less development period.
The first stage is often referred to as “crawlers” because it is the only time in the life of a scale it can be mobile.
The first generation of scale on a tree or shrub will emerge as nymphs in spring or early summer. In one year, we can see three or four generations of scale!
Crawlers search for a suitable location on the plant on which to settle and feed. They will often all gather toward the undersides of young horizontal branches instead of the parts exposed to the sun. Once they settle, the crawlers will have their first molt.
The maturing male will develop wings and retains the use of their legs, and will die within 2-3 days. Because they still have their legs and have developed wings, the male scale will still be able to move about.
On most species, the wings are most unusable and scale will rely on their legs to move them about. Although they will travel with the wind and use the wings to guide their bodies.
The female scale will lose the use of their legs as they approach adulthood. The female scale will produce waxy white threads that become felted or matted into a thick whitish covering over their body.
Adult females are felt-like white or gray encrustations that stick to crape myrtle parts ranging from small twigs to large trunks. When crushed, these scales exude pink “blood”-like liquid.
The adult female lays eggs under their covering from May to September and then it will die. These crawlers emerge from under the “mother scale” and disperse within a day or two.
Scale spreads in 3 primary ways. Firstly, as mentioned earlier, male aphids can travel by wind using their wings to guide them. Luckily, this does not produce too much of a threat to the neighboring landscapes since there would need to be females there to reproduce.
The second way is the crawler nymphs can be spread via birds and wind. This would bring both male and female and can begin an infestation to a new tree or shrub. The final way and most primary means of spread are through ants.
The female scale will produce honeydew, which can bring ants to “mine” the sugary substance. Some species of ants will actually “attend to” the female scale in hopes of fresh honeydew.
These emerging crawlers find themselves on these ants and then can spread dramatically from there.
There are some natural means to treating scale. An easy way to prevent scale is to carefully inspect any new tree or shrub at the nursery and look for sign of scale before bringing it home. This way you are not bringing home a problem waiting to happen.
Scale also has many natural enemies—small parasitic wasps, ladybird beetles, and some fungi—which can significantly reduce scale insect populations.
A ladybird beetle, also known as a ladybug, is easy to spot, but parasitic wasps are more difficult to see because they are so small. Parasitic wasps often emerge from scales by chewing small, round holes in them.
It’s important to note that if ants have begun “attending to” the scale for honeydew, natural predators will be ineffective because the scale will be reproducing at a much faster rate than the predator can keep up with.
If natural enemies are present and it appears that there are few scale insects or that no ants are attending them, wait a few days and check again. If natural enemies are controlling the scale infestations, you may not need to use pesticides.
If insecticide treatments are needed, a study by Texas A&M found it to be most effective in April through September.
Regardless of the number of applications needed, you must cover the plant thoroughly with insecticide each time, particularly when you’re using contact insecticides. Cover both sides of the leaves and all the twigs and branches.
It is possible that these scale insects overwinter (spend the winter) as adult females or eggs. In Texas, crawlers and later-stage nymphs have overwintered under loose bark and in cracks and crevices.
To prevent this, it is crucial to apply horticultural oil in the winter at dormant season rates to the bark and crotches of the plants where the scales shelter. Use enough oil to reach behind loose bark and into cracks and crevices.
Winter is an especially good time to treat for scales! Cover the tree thoroughly with pesticides, and when using oil.
Dormant oils should be applied on trees and shrubs before spring growth begins when temperatures are above 45 degrees F for 24 to 48 hours. Follow the instructions on the product label on how to dilute and apply the pesticide.
Professional Tree & Shrub Service
Regulations on insecticides and dormant oils change frequently. In order to ensure you are using products safely and effectively. You may want to consider reaching out to a professional tree and shrub service.
At Gecko Green we offer an amazing 8 round treatment program for trees and shrubs that can prevent infestation like scale and many more! Call us today for a quote to protect and treat your landscaping.