The following question was sent to the P&PDL diagnosticians here at Purdue University:

Question: I have black scalelike insects covering the twigs of a five year old Tulip tree. During August, there are also scalelike white/grey fuzzy insects that actively crawl around that I assume is a mobile stage of these scales. Also the tree is surrounded by wasps, bees, and other insects. What should I do?

Answer: It looks like your problem is with an insect called a tulip tree scale. These insects are immobile as adults and are usually dark in color. After they hatch from their egg, the crawlers are mobile. These insects break down cells for sap and other nutrients in the tree and excrete a clear substance called honeydew. This sugar-like substance is a favorite meal for ants, bees, wasps, and a fungus called sooty mold.

Repeated heavy infestations can result in death of branches. The use of pesticides can be detrimental to beneficial insects, such as lady beetles and microscopic wasps which are natural enemies of the scales. However, if infestation is severe, it is possible to kill the crawlers during mid-August when they are active using a systematic insecticide. Then use a dormant oil spray next spring. When using pesticides, read and follow label directions.

--Nathan E. Saxe (June 9, 1998)

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