Question
Colorado Springs CO.  I have two Aspen trees in my yard that have black edges on some of the leaves.  The leave is green and looks healthy, but the edges are black and crusty.  I've seen some black ants on the tree, but not eating the leaves.  I'm trying to find out what is causing it and how to fix it.  Any advise?

Answer
The most common foliar problem on aspen is aspen leaf spot caused by the fungus Marssonina populi. This fungus causes dry, brownish lesions with yellowish borders . Margins are often irregular andindistinct, and not restricted by veins as are those caused by iron chlorosis. Infection is favored by wet weather, especially when the aspen leaves are emerging from the buds. During particularly wet springs, extensive infection can occur throughout aspen forests, resulting in massive defoliation and a loss of the delightful fall color. After several years of defoliation the disease may even kill aspens.In the home landscape, the impact of this leaf spot can be minimized by increasing the vigor of trees by proper watering and fertilization. Vigorous trees can produce new leaves, free of disease, that can make the sugars that the tree needs to continue growing. In most cases, increasing vigor is all that is needed to ensure tree survival. When trees have been defoliated two or more consecutive years, or the trees are 搆ey?landscape trees, fungicide use may be warranted.Labeled fungicides include chlorothalonil (Daconil 2787, Daconil Lawn and GardenFungicide, Broad Spectrum Funagicide) or fixed copper fungicides (Microcop, Copro, Kop-R-Spray, Kocide 101, Champ). One of these fungicides must be applied at label rates beginning at bud break and applications should be made at 10?4 day intervals as long as wet weather continues or until leaves reach their full size. Sprinkler irrigation on foliage should be avoided because it creates conditions favorable for infection and can spread spores. Destroying fallen leaves is often recommended for controlling this and other leaf diseases. However, this practice may be of limited value because spores of leaf disease fungi can often travel great distances from untreated aspens and thousands of spores can be produced on leaves that remain. In dry years, removing the nearby source of spores is of little benefit because conditions do not favor infection; in wet years, a single spore source can provide enough spores to infect many trees. Therefore, nothing more intensive than the normal fall leaf raking is necessary