What Is Wrong With My Aspen Tree?

Do the leaves have spots or blotches?

Are there any rust-colored spots on foliage?

Are there any patches of bright orange bark that (usually, but not always) ooze brown liquid?

Are the leaves yellow, branches, and leaves are covered with small bumps?

Do the leaves have holes?

Are the leaves distorted and yellow?

Are the leaves stippled with yellow and the foliage is webbed?

Your plant is suffering from a fungal leaf spot. These can come from several fungus diseases, causing spots to occur on foliage. Spots may enlarge rapidly, especially in wet weather. Destroy infected leaves or plants. Spray plants with sulfur to prevent the disease from spreading, especially if the weather is wet. Spray between rains. Prevent problems by thinning plants to provide good air circulation.

Rust-colored spots on foliage indicate a fungal disease - Rust. Provide good air circulation around plants by thining them. Avoid making leaves wet when watering. All infected leaves should be removed. Spray leaves with sulfur early in the season to prevent rust or to treat mild infections.

Cytospora canker is a common aspen tree problem. This fungal disease causes patches of bright orange bark that (usually, but not always) ooze brown liquid. After a few years, the bark begins to fall off and you’ll see dark brown or black areas beneath it. There is no cure for canker. Protect your tree from winter injury.

Oystershell scales are an important pest of aspen trees. Scrape off minor infestations with your fingernail. Prune out badly infested growth, or use a soft brush and soapy water to gently scrub the scales off the stems. Control scales by spraying insecticidal oil during the growing season.

Several species of leaf-feeding caterpillars will feed on the aspen leaves. They may also feed on stems, flowers, and fruit. Handpick and destroy caterpillars, or spray plants with BTK if caterpillars are feeding. Many foliage-feeding caterpillar populations are controlled by general predators, parasites, or naturally occurring viruses.

Distorted, yellow leaves are caused by aphids. These tiny insects cluster under leaves and on growing tips where they feed on plant sap. Leaves, stems, and buds get distorted, and later leaves and flowers drop from the plant. You can control them by washing them off the plant with water spray. Insecticidal soap should be used with severe infestations.

Leaves stippled with yellow and webbed foliage is caused by spider mites. These tiny, spider-like pests feed by sucking sap from the underside of the plant's leaves causing yellow flecking on the upper leaf surfaces. You can control spider mites by spraying plants thoroughly with water 2-3 times a day for several days. For severe infestations, spray plants with insecticidal soap, or pyrethrin as a last resort.

Wandering, white or translucent tunnels in leaves are caused by aspen leafminers. Leafminers prefer young, tender foliage and cannot tunnel in hardened leaves. Avoid applying nitrogen fertilizer while populations are high, or the new growth will be severely damaged. As pruning too frequently can also stimulate new flush growth, avoid pruning live branches more than once a year, so that cycles of flush growth are uniform and short. Do not prune off leaves that have been mined—the undamaged areas of the leaf are still able to produce food for the tree.