Woolly aphids generally are not much cause for alarm, although they can cause unsightly damage to plants, which is particularly a problem for growers of ornamental plants. Symptoms caused by their feeding on a plant include twisted and curled leaves, yellowed foliage, poor plant growth, low plant vigor, and branch dieback. The woolly apple aphid,
Eriosoma lanigerum is a widespread pest of fruit trees, feeding principally on apple, but also, pears, hawthorn, ash, alders, elms and oaks. Gall making species include
Melaphis rhois and Pemphigus spp. Further minor damage can be caused by the
honeydew that woolly aphids secrete, which is difficult to remove. While the honeydew itself doesn't cause too much of a problem, the honeydew can cause sooty mold to grow, which can block some of the sunlight needed for
photosynthesis. Woolly aphids and other sucking insects are often
vectors of transmission for
powdery mildew (a white
fungus which grows on above ground parts of some plants), and other infectious diseases. Typically woolly aphids in
subtemperate climates precede and are an indicator of various plant
infections, including powdery mildew. Aphids penetrate plant surfaces where they often reside and provide a host of potential
inoculants through physical, digestive or
fecal secretions. Aphids are often an indicator of other potential plant problems. ==Taxonomy==