Sticky situation for homeowners in northern Michigan

Abundant Lecanium scale populations result in sticky sap, coating everything in the yard.

This summer, northern Michigan residents and visitors are battling a sticky substance that appears to adhere to anything and everything in the yard. It has been reported to several Michigan State University Extension offices that this substance is even covering furniture under the cover of awnings, leading to serious frustrations.

The cause is likely the Lecanium scale, a widespread, naturally-occurring insect in Michigan. The scale has been observed in great numbers on hardwood trees, particularly oaks, throughout northern Michigan. The scale also has the ability to thrive on maples, dogwood and fruit trees. The sticky substance that has everyone trying to find a safe zone in the yard is sugary water secreted by the insect while it feeds on the sap of the tree in which they live. Essentially, it’s the waste of the insect. 

Life cycle

We are most likely to see the immobile, reddish to brown hemispheres, about 1/8 to 1/4 inch in diameter, that line and sometimes cover smaller branches. These hemispheres, or scales, are a protective covering under which the insect overwinters in its immature stage. The scales mature in early spring, and females lay a large number of white to pale yellow eggs under her protective body. The eggs hatch into crawlers usually in June. Crawlers are extremely tiny and can usually be found on the underside of the leaves of the infested tree. The crawlers feed on the sap while stationed on the underside of leaves until late summer, usually in August. At that time, the crawlers migrate back to the small branches and twigs where they will overwinter in an immature stage until the following spring. In the crawler stage, the insects can move from tree to tree via wind currents, bird’s feet and even on the sleeves of our shirts.

What’s that sticky stuff?

The sticky substance that coats everything within the vicinity of an infested tree is actually “honeydew”, or excess fluid that is excreted in abundance as the insects feed. Leaves on trees and plants under an infested tree can be coated with the substance, as can vehicles, decks, furniture and everything else. On trees, an abundance of the honeydew can lead to the development of a black, sooty mold, which is a fungus that sometimes grows on the substrate.

Honeydew may be removed using products that also remove pitch from a pine tree. Rubbing alcohol as well WD-40 lubricant and Skin-So-Soft bath oil (using the oil will require washing the car after use) will help to remove the sugar water. As with any product, use it on a small area prior to application to the entire vehicle or other item. When using, give the product some time to work rather than expecting an immediate response. Washing the substance off of people and pets can easily be accomplished with soap and water.

Treatment may not always be recommended

The Lecanium scale is usually not fatal to a tree, although it may cause some smaller branches or twigs to dieback. In cases where the scale is heavily infesting a tree and other stressors, like drought or secondary insects are present, the scale may contribute to the general decline of the tree.

The Lecanium scale has biological controls that usually control the ever-present populations. While the scale population is extremely high this year, we can rest assured that the boom in scale population will likely be followed by a boom in its biological controllers in the near future, which will bring scale levels back to normal levels. The list of predators and parasites that attack the Lecanium scale is long and includes ladybird beetles, lacewings and other insects that feed heavily on the crawler stage. A parasitic wasp also uses the hardened scale for larval development. And the list goes on.

Chemical treatment of the scale will also treat or kill the biological predators. Therefore, treatment should be carefully considered before executing. If deemed necessary, the crawler stage of the insect may be treated from mid to late summer when the crawlers are actively feeding on the undersides of the leaves. Timing is crucial to be effective. Use a hand lens to be sure crawlers are present prior to treatment. Several insecticides can provide effective control through spray applications to the leaves. Applications may have to be repeated to effectively kill the crawlers. Beneficial insects will also be affected. When the scale is in its overwintering stage, dormant oils can be applied to suffocate the insects. Lastly, systemic control can be provided by applying a pesticide that contains imidacloprid. Pesticides containing imidacloprid are usually mixed with water and poured around the base of the tree. Always follow label directions when using chemicals.