Solving Ash Problems

Cultural Problem with Seeds

Ash trees produce enormous numbers of seeds that fall all over the yard. The many uninvited seedlings that result are often a nuisance.
Trunks Weakened, Scarred; Knots on Limbs, Twig Drop indicates Borers

The ash borer is a moth whose larvae bore into tree trunks at or below ground level, often damaging trees so badly that they can be easily pushed over. They also render trees vulnerable to disease. Carpenter worm is a moth whose larvae form large scars along the trunk, especially in branch crotches. Lilac borer is a moth whose larvae cause rough knotted swellings on the trunk and limbs. Small branches break off at the point of injury. Other borers infesting ash include brown wood borer, California prionus, flat-headed apple-tree borer, and Pacific flatheaded borer. Control borers by cutting down and destroying badly infested trees. On young trees, predatory nematodes can be effective in killing borers.

For more information see the file on Dealing with Borers.

Galls on Flowers mean Mites

Ash flower gall mite is only about 1/50 inch long. It is related to the spider and has four pairs of legs and piercing-sucking mouthparts. Infested male ash flowers grow abnormally, developing irregular galls up to 1/2 inch in diameter. These galls dry out, forming clusters that are obvious during the winter when the tree has no leaves. A high-pressure water spray will often dislodge mites and interrupt their attack. If that does not work, spray them with insecticidal soap.

For more information see the file on Dealing with mites.

Small Bumps on Leaves and Branches; Stunted Growth indicates Scale

Oystershell scale and scurfy scale attack ash. The pests overwinter in the egg stage and then begin to feed in May under protective teardrop-shaped waxy shells. These shells are about 1/10 inch long, and cover twigs and branches of affected trees. Spray the tree in the early spring before the leaves appear with dormant oil to smother the eggs. Later in the season spray with the insecticidal soap.

For more information see the file on Dealing with Scale.

Leaves Notched means Weevils

Japanese weevils are beetles about 1/4 inch long. They vary in color from light to dark brown, with striations on the wing covers. They feed on ash foliage during the day, damaging the edges of the leaves. At night they find shelter under tree bark and yard debris. When startled while feeding, they will drop suddenly to the ground. Disturb tree branches and catch the dropping weevils in a cloth spread on the ground underneath the tree. Smear the trunk with sticky tanglefoot near ground level to prevent the weevils from climbing up the tree to feed. Spray any visible weevils with pyrethroid insecticide. Predatory nematodes have also been used effectively against weevils. Just apply them to the soil under the plant.

Reddish-Brown Spots on Bark shows there is Canker

Six different fungi have been identified as causing cankers on ash trees. Often accompanying the devastating disorder called ash decline, these opportunistic fungi attack trunks and branches, making reddish brown spots on smooth bark. On older, rougher bark the cankers are not readily visible. Prune out affected branches. Encourage tree vigor by attentive feeding, watering, and mulching.

For more information see the file on Dealing with Fungal Disease.