Maple trees with white fluffy, stringy things on their leaves and twigs have woolly alder aphid (Paraprociphilus tessellatus). Populations seem rather high this year. This aphid species requires both alder and maple to complete its life cycle, spending spring and summer on maple and the remainder of the year on alder. While on alder they are a plump, bluish colored aphid covered by white, waxy filaments. They will often be found in a group, forming a solid mass of white fluff on the stems.
When present on maple they are sometimes referred to as maple blight aphid. They don’t usually do any significant damage to either maple or alder but they can be quite noticeable at times because of the large patches of fluff when they congregate in an area. High populations of these aphids on maple can create enough honeydew (aphid excretions) to create a sticky layer on any objects underneath the maples. Sooty mold can then grow on the sticky layer, so it is recommended to wash off things under these trees on a regular basis. I’ve seen or had reports of woolly alder aphids on maple from Door, Langlade, Oconto, and Oneida counties.
Written by: Linda Williams, forest health specialist, Woodruff, (Linda.Williams@wisconsin.gov), 715-356-5211 x232.