If you have beech trees in your yard or nearby woods, here’s something fun to look for at this time of year:  spongy sooty mold of beech.  The sooty molds are fungi that grow on honeydew, a sweet substance excreted by aphids and some other insects.  They are called sooty molds because they grow in black layers on leaves and other surfaces where honeydew has dripped from aphid infested plants.  Sooty molds are not plant parasitic but they can affect the health of a plant when abundant by preventing photosynthesis as a result of blocking sunlight from reaching the leaves. 

Back to spongy sooty mold of beech.  This sooty mold is unique because it forms a large, spongy mass on beech branches instead of just a thin layer of growth.  These black masses are easy to spot this time of year when the leaves have fallen. 

As mentioned above, sooty molds grow on honeydew excreted by insects.  Many sooty mold fungi will grow on honeydew from a variety of insects, but another unique characteristic of spongy sooty mold of beech (Scorias spongiosa) is that it only grows on honeydew from the beech blight aphid, Grylloprociphilus imbricator, also known as the beech woolly aphid.  This aphid lives in colonies so their honeydew is concentrated in relatively small areas in heavy amounts, and this is what enables the sooty mold to grow so large.  The beech woolly aphid, as the name implies, are covered in a white waxy coating.  Look for them in late summer to early fall.  The sooty mold growth is initially a thin layer of yellow brown tufts containing pycnidia, the asexual fruiting bodies of the fungus.  As more honeydew accumulates, the fungus grows larger and becomes spongy.  Later, it will blacken and produce sexual spores in structures called pseudothecia.