Q: I have a powdery like substance on my maple tree which I understand is some sort of scale. Will this hurt the tree and should it be treated?

Richard from Tulsa

A: If the substance you see is on the bottom of twigs and looks like wet popcorn hanging there, this is cottony maple scale.

Cottony maple scale can, if it's a heavy infestation, devastate a maple. Often you'll find them heavily encrusted on just a few branches, but they can spread from there, so it might be wise to treat the tree to reduce their expansion.

You can spray the tree, but this should be done by a professional. I recommend having an oil application done in spring, then another spray in early July. Some recent information indicates than another spray in Late July and during September can also reduce the number of "crawlers" (baby scales, as it were) found on the undersides of the leaves.

This would be a worst-case scenario, having to spray this many times. You might need multiple applications the first year, but should be able to taper back to maybe just the oil application in spring from there on out.

However, you describe the symptom as a powdery substance. This sounds like powdery mildew, which is often brought about by temperatures in the 60-80 degree range and high humidity.

Unless the mildew totally covers leaf surfaces, thereby reducing the amount of sunlight the leaf gets (which reduces photosynthesis), mildew is usually not much of a problem. If it HAS completely covered too many of the leaves, then you might want to treat but this needs to be done on a preventative basis.

Begin a 3-spray program in mid-spring, spacing your treatments about 3-4 weeks apart, using a material labelled for mildew control.

You might also be able to control mildew by pruning. By thinning the tree out you improve air circulation and sunlight penetration, thereby allowing the leaves to dry sooner after a rain. Removing nearby plants if the area is too crowded will also help.

Since you are from Tulsa, I'd recommend that you contact a local arborist to check this out. You may have different scales or mildews there than here in Cleveland.