Defending your trees from tuliptree scale

Have you gone out to your car parked under a large tree and noticed that it was coated with a clear or black sticky substance? Perhaps your deck or lawn area under a large shade tree is coated with this same clear or black sticky substance. The tree is probably a tulip poplar, also called yellow poplar or tulip tree (Liriodendron tulipifera).

The sticky substance, called honeydew, is the secretion of an insect called tuliptree scale (Toumeyella liriodendri). The female adult is a flattened insect, usually 5 to 7 millimeters in diameter. She looks like a grey-to-pink-to-orange bump on a twig. Her mouth parts are like a hypodermic needle. She inserts her mouth into the twig and sucks out tree sap.

The insect life cycle begins in June when mating occurs. The female gives birth to up to 3,000 crawlers that move around the tree and find a place to call home. They insert their mouth parts and begin feeding for a short time. At the end of the crawler stage they molt. The next stage results in the nonmobile bump. At this time the insect continues feeding until next spring when the cycle begins again.

Over a long period of time, an infestation of scale on tulip poplar can result in its demise. On the other hand, if the infestation can be controlled, the tree will recover fairly quickly.

One method of control is to spray the entire tree with refined horticultural oil. During the summer two to three applications of the oil will help control the infestation. You should also spray the tree each February for two to three years in order to get better coverage and control of the infestation. The oil forms a film over the scale and results in suffocation of the insect. Therefore the tree must be thoroughly covered with horticultural oil.

These two treatments, Tree & Shrub Systemic Insect Drench and Horticultural Oil Spray, can be used to treat scales such as the ones on this branch from a tulip poplar tree. (Laura Simon)

If the tree is large, spray applications are impractical. In that case the use of a systemic insecticide drench can control the infestation. Imadicloprid is often used for this application. Be sure and read the label for specific application instructions.

Typically the insecticide is mixed in a 5-gallon bucket of water and poured around the stem of the tree. The amount of insecticide used will be determined by the circumference of the trunk. After application to the soil, water around the tree so the insecticide moves into the soil. It is then taken up by tree roots and moves into the twigs. When the insect feeds it imbibes some of the insecticide and dies.

If you just now notice the infestation, go ahead and make the application of the insecticide drench at this time of the year. But in addition, make sure you also make the drench application next spring, preferably in March. This is the time when large quantities of sap are moving up into the tree in order to provide nutrients for plant growth. The efficiency of insecticide uptake is much better at this time of the year.

As stated above the tulip tree scale is generally not lethal to the tree. On the other hand, the infestation can result in a mess to clean up on your car, patio, and lawn.

Send your gardening and landscape questions to Paul Schnare at P.O. Box 699, Cape Girardeau, MO 63702-0699 or by email to news@semissourian.com.