Scale insects on trees are not something you want to have to deal with.
They’re waxy insects that pierce trees with their mouths and suck sap from them. This makes it more difficult for trees to maintain moisture and nutrients in the short term. The honeydew that scale excretes onto trees can provide sustenance for sooty mold that can cause further infestations and damage to trees.
There are more than 60 varieties that occur in Michigan, and many times they are not noticed or are ignored until tree or shrub branches start to die. So, let’s take a look at some of the negative effects scale infestations can have on tree health and the importance of applying treatments as quickly as possible.
Types of Scale Insects
Soft (Lecanium), kermes, and bark scales produce honeydew. These scales feed directly on plant parts that transport fluid and nutrients. This can reduce plant growth and cause leaf drop or branch dieback. The most common symptom of soft scale infestation is an accumulation of honeydew and sooty mold on or beneath a plant.
Armored scales do not produce honeydew. The armored scale’s straw-like mouth moves like a plumber’s snake to burst plant cells and feed on their contents. This can reduce plant growth and vigor. Common symptoms of infestation include premature leaf drop and branch dieback.
Pit scales are likely to do the same to the raised plant tissue that surrounds them. If there are large numbers of scale, the pits coalesce, making the twig surface appear dimpled and roughened. Feeding by oak pit scales can kill twigs and the dead leaves remain on infested twigs through the winter.
The Juniper scale is a very common and sometimes serious pest of juniper. They are light gray or white, very small, and nearly circular. They like to attach themselves to the underside of the needles, rather than the bark.
One of the first signs of an infestation is when leaves on individual branches begin losing their color and may eventually die.
Lecanium scale and Cottony Maple scale are the most common in Southeast Michigan. They will cover the branches of silver maple, honeylocust, and many other species of hardwood trees in our area.
The biggest problem comes from the droplets of honeydew raining down from infested trees in May and early June. Honeydew is the sugary liquid waste excreted by scale insects. A considerable amount of honeydew is excreted because scale insects need to suck a lot of sap from trees in order to get the amount of protein they need for growth and development.
Another problem that can develop is mold. The honeydew is often mistaken for tree sap as it covers cars and buildings under infested trees. The accumulation of honeydew can lead to the growth of black, sooty mold. Finding sooty mold under a plant is often the first indication that there are scale insects, but it may also indicate aphids and other sucking insects.
Scale infestations rarely kill trees but can damage them and be especially hard on young trees. Even the most mature trees that are infested can become thin and experience branch dieback. And repeated heavy Lecanium scale infestations can kill branches or crown dieback in trees.
When Do Scale Insects Appear?
There are typically two times of the year that scale insects become active. It’s because there are two generations in Michigan. The first hatching in early to mid-June, and the second in late July or early August.
How To Control Scale Insects
The good news is that there are ways to control scale populations. These natural predators can be held in check, even after you’ve noticed eggs on your trees and shrubs. A proactive approach is best.
But keep this in mind, scale insects are not easy to control with traditional contact insecticides because of the covering that protects their bodies.
The most effective control strategy is to spray with insecticides, beginning at egg hatch, when the so-called crawlers first appear. Use insecticides during the hatching period when crawlers are first observed will provide maximum effectiveness.
You don’t have to let scale insects destroy your trees! If you’d like to find out how to get them under control or from ever showing up in the first place, feel free to contact Safari Tree. One of our professional arborists will be happy to give you a rundown of the quick, effective treatment and prevention services we offer.