Editor's note: Get Growing, written by the La Plata County Extension Office's Master Gardener Program, appears every other week during the growing season. It features timely tips and suggestions for your garden and landscape.As the warm weather finally arrives, the telephone calls about "why aren't my tomatoes growing?" have turned to "what is wrong with my aspen tree?" I will tread lightly on the topic of aspens, as I have found some people hold the trees dear to their hearts. Understandable. They are beautiful trees.
But like the beautiful rose, they come with a long list of diseases and insects that love them as well.
Aspen leaf spot. Fungal disease that arrived early with our "June-soons." Usually not fatal, but repeated infection and defoliation can greatly stress the tree. Water early in the morning so leaves can dry out and fall. Removal of infected leaves can reduce the severity of the disease.
Cytospora canker. Very common disease that will quickly invade wounds. Identified by the orange to brown to black discoloration (ooze) that is often associated with a sunken dead area of bark. It is tough to manage, but try reducing stress on trees, remove infected limbs and clean wounds (no pruning paints).
Oyster shell scale. Tiny, quarter-inch-long brown or gray shells that form a solid "crust" along the trunk and branches.
They suck sap from the bark, and can often kill branches or the entire tree. For control, scrub with a soft plastic scrub pad (careful on young trees), or use a horticultural (dormant) oil before bud-break in spring.
Twiggall fly. Produces spherical swellings that look like someone tried to shove a marble up the twigs. Formed by insects, the galls are usually not fatal, but multiple galls on one twig can kill it.
Eriophyid mites. Rarely kills a plant, but their feeding can cause deformed leaf tissue, causing the leaf margins to look "blistered." Because they overwinter on the plant, they may be controlled with horticultural oils.