Sticky droplets raining down from Magnolia trees

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

The honeydew excretions from Magnolia scale can make a mess of cars or bikes parked under them. Also, yellow jackets are attracted to the sugary honeydew. Finally, if there is enough scale, the foliage and branches under the scales may start to turn black from sooty mold fungus growing on the honeydew. All of this is a result of a heavy infestation of one of our largest soft scales in North America – Magnolia scale. The young scales present now are covered with a white powder. Later in the summer they will turn dark brown. Unfortunately, they have been very difficult to control with insecticides. Some arborists have used Merit (imidacloprid) soil drenches each April or May with spotty records of success. The imidacloprid drenches will probably take two years before being effective, and not even that is guaranteed. Meanwhile, spraying is the only remaining option (other than replacing the trees). Talstar has been effective on most of the soft scale insects, but in this case, you will probably need two applications two weeks apart starting at this time to make a good dent in the infestation. Some of the new neonicotinoid insecticides have been very effective on soft scales and mealybugs. You may want to try foliar sprays of Flagship, Safari, or Tristar for Magnolia scale, cottony maple scale or other troublesome soft scale insects.

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