What Is Wrong With My Alder Tree?

Are there any discolored, sunken cankers on twigs, stems, and trunks; orange fruiting bodies may be present?

Are the leaves covered with white powder?

Are the leaves pale on their upper side and are there any dusty blisters on the undersides?

Are the leaves curled and distorted?

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

Does the whole tree declines, small holes are present in stems?

Are there any silky caterpillar tents in the branches in late summer?

Do the twigs have clublike galls on them?

Are the leaves pale and mottled?

Are the leaves riddled with small holes?

Nectria canker on trees is a fungal infection. The pathogen known as nectria invades fresh wounds and damaged areas of bark and wood. Orange fruiting bodies appear during spring and summer. Nectria rarely kill older, established trees. There is no cure for nectria canker. Prevent it by avoiding pruning during wet conditions, and by protecting your trees from winter injury.

White, powdery patches on the leaves are caused by a fungal disease Powdery mildew. Powdery mildew usually appears in damp places. Encourage good air circulation around the affected plants by thining them and any surrounding plants. Water plants from bellow to keep foliage dry. Any affected leaves should be cut off and removed. The appropriate fungicidal spray will protect your plant from further infections.

Likely cause for these symptoms is 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.

Distorted and curled 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.

Oystershell scales are an important pest of alder trees, especially in the Midwest. 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.

Holes in stems are made by tiny beetles called shothole borers. Shothole borers prefer injured or diseased trees and shrubs. Prevent attacks by maintaining the vigor of the tree. Cut and burn any dying stems below the borer holes. In June, crush any visible eggs. During the summer season, check to see if fine boring dust is being pushed from small borer holes. Cut out holes with a sharp knife. If the tunnels are fairly straight, kill the borer larva by probing the tunnel with a flexible wire.

Fall webworm is a caterpillar that makes silky tents during Fall. Fall webworms are usually held in check by songbirds, yellow jackets, wasps, and rodents. You can easily remove the webs when they occur in trees. Insecticides are seldom necessary for fall webworm, especially in trees, and should be considered only if the infestation is heavy. Bacillus thuriengensis (BT) can be used when the caterpillars are small, but it will not provide satisfactory control once the webs are large.

Gall midges are insects whose orange larvae tunnel into young shoots. One-inch-long swellings form around the developing larvae on the twig. Leaves on the branch may wilt or turn brown. Prune off and destroy galls as soon as you see them.

Lace bugs are flat, dark-colored insects with lacelike wings that feed on the undersides of leaves. They cause leaves to turn yellow, then brown, and eventually die. Treat plants with a commercial pyrethrin spray or dust if the damage is severe. Prevent problems by covering plants with row cover until they blossom.

Small holes in leaves are caused by Alder flea beetles. Larvae are small and white, feed mostly on the undersides of leaves. Control severe infestations by spraying or dusting plants with pyrethrin.

Yellow, stunted trees, and roots that have swollen galls indicate root-knot nematodes. Other symptoms are plants wilting during bright, hot days. Prevent root-knot nematodes by applying parasitic nematodes or solarizing the soil before planting.