Cottony maple scale

Cottony maple scale

Name: Pulvinaria innumerabilis

Alias: Cottony maple scale. This is the most un-bug-like insect you will come across. Quite often it is mistaken as some sort of fungus or scab that grows on the side of a plant. The female nymphs of all scales embed themselves on the bark of a tree, where they will stay for the rest of their life. They have a shield on their back that is a quarter of an inch in diameter. They spend their entire life under that shell, avoiding any interaction with the world and feeding off the tree. Male insects are mobile, and they take the time to go to the females, because they won’t move.

Crimes: After they have mated, the cottony maple scale insects will explode with a large cloud of silk out their back end that enhouses thousands of eggs that will move on and cover other trees in these “scales”. They feed off the tree and deprive it of nutrients that are needed. Tree symptoms often look like nutrient deficiencies, when in fact it is an insect problem. The other obvious signs are if the tree is covered in scales or covered in little marshmallow like puffs.

Redeeming qualities: None

Sentence: They really aren’t too bad in small numbers, and if you can tolerate them then usually a population of natural predators will keep them at bay. However, often their populations become so great that they kill trees and bushes. Simple over the counter insecticides will take care of them. As spring application an insecticidal soap can prevent them from sticking to the bark. Other insecticides such as carbaryl, malathion, and permethrin are also effective. Applications in the spring are usually more effective than in the summer months.

For more information on dangerous and beneficial bugs, call UI Extension educator Joseph Sagers at 208-270-4031 or email

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