| Dogwood Problems | |
|---|---|
| Symptoms | Probable Cause |
| Leaves Spotted; Dieback; Cankers | Dogwood Decline |
| Slow Growth; Pale Foliage | Root Competition |
| Tunnels Under Bark; Branches Girdled | Dogwood Borers |
| Small Bumps On Leaves And Branches | Scale Insects |
| Sunken Spots On Leaves | Spot Anthracnose |
| Leaves Stunted; Swellings On Trunk/Roots | Canker |
| Flowers; Leaves Or Twigs Wilt | Blight |
| Bark of Stems and Roots Gnawed | Rodent Injury |
Leaves Spotted; Dieback; Cankers are Caused by Dogwood Decline
Since 1977 a dogwood decline disease has been steadily spreading throughout the Mid-Atlantic states. Its cause has been determined to be a fungus (Discula sp.), whose spread appears to be fueled by damp spring and fall weather. Usually the first signs are that a lot of the leaves don’t fall off in the fall like they normally do. Then in the spring, both backyard and woodland flowering dogwoods develop sunken spots on the leaves. Small end twigs die back and sometimes trunk cankers develop. Progressive twig dieback in the lower part of the tree signals advanced decline and is often accompanied by borer attacks. A tree in advanced stages of decline may die within 2 seasons. However, carefully pruned cared for, it might live 4 or 5 more years. Then it will need to be taken down.
To minimize risk of infection, locate young flowering dogwoods where they are not stressed by hot summer afternoon sun, yet enjoy good air circulation. Plant the rootball slightly higher than it was in the nursery container. Water faithfully during dry spells, giving trees at least 1 inch of water every 10 days. Fertilize in the spring with a product that features slow-acting nitrogen. Clean up organic debris which might shelter disease and insects. Do not prune when leaves or twigs are wet. Disinfect pruning equipment by dipping it in a solution of hot water and household bleach. Plant a decline-resistant kousa dogwood (Cornus kousa) instead.
Slow Growth; Pale Foliage Caused by Root Competition
Dogwood tree growth may be inhibited by turf cover--grass or weed plants--growing on the soil surface right up to the base of the trunk. Remove this competition for soil nutrients and moisture by clearing a 1 to 2 foot diameter circle of bare soil lightly covered with mulch around the base of the trunk. Do not allow the mulch to touch the trunk.
Tunnels Under Bark; Branches Girdled means Dogwood Borers
These moth larvae, white with light brown heads, tunnel just below the bark. The adult moths have clear wings with blue black edges, and lay their eggs in roughened or damaged spots on the bark. As many as 50 larvae may infest a 2 foot section of a dogwood trunk. Spread a ring of mulch on the soil around the tree trunk or fashion a tree guard of plastic or cardboard around the dogwood's trunk to prevent lawnmower injuries to the bark. The guard will also protect it from gnawing rodents. Prune affected branches below visible borer holes and discard in the trash. For more information see the file on Controlling Borers
Small Bumps On Leaves And Branches are Scale Insects
Scale pests form groups of small waxy bumps or blister-like growths on dogwood stems and leaves. They are shells that protect the scale insect beneath while it feeds on tree tissues. The shells may be white, yellow or brown to black, and are only 1/10 to 2/5 inch in diameter. The first sign of a scale attack is often discoloration of the upper surfaces of dogwood foliage. Then leaves drop, the rate of growth slows, and twig tips die back. Some scale species excrete a visible sticky honeydew which coats foliage and encourages ants and the growth of a gray sooty mold that coats leaves. For more information see the file on Controlling Scale
Sunken Spots On Leaves are Caused by Spot Anthracnose
This fungal disease causes pinhead sized spots on dogwood leaves in the spring, especially in very wet springs. Spots may appear on the petals (bracts) as well, which remain small and distorted. While this disease makes the tree unattractive, it does not kill it. Proper location and careful maintenance will help the tree fight this disease which is aggravated by moist, cool, shady conditions. Keep it free of stress by fertilizing, mulching and watering as recommended. Prune away dead or diseased branches and collect and discard all fallen leaves and discard them in the trash. Disinfected any tools you use on the diseased tree by dipping them in a solution of hot water and household bleach. For more information see the file on Controlling Fungal Disease
Leaves Stunted; Swellings On Trunk Or Roots Due to Canker
Crown canker, caused by a fungus, occurs primarily on transplanted dogwood trees. Leaves are smaller and lighter green than normal, and turn prematurely red in late summer. Twigs and even large branches die. Within a year or two the entire tree is affected. The canker slowly develops on the lower trunk, at or near the soil line or on the main roots. Eventually it girdles the tree. Crown canker cannot be controlled after the fungus has invaded most of the trunk base or root collar. Control is possible if the infection is confined to a relatively small area at the trunk base. Remove a strip of healthy bark about 1 inch wide from around the edge of the canker. Gouge out all discolored bark and sapwood. Do not wrap or paint the wound; just let it heal in the air. For more information see the file on Controlling Fungal Disease
Flowers, Leaves Or Twigs Wilt Because of Blight
Blight diseases caused by several kinds of fungi sometimes attack dogwood flowers, leaves and growing twigs, causing discoloration, wilting and death. Cankers may develop on twigs. Prune out the dead twigs. Improve the vigor of the tree by providing proper amounts of fertilizer and water. For more information see the file on Controlling Fungal Disease
Bark of Stems and Roots Gnawed by Rodents
Small rodents sometimes gnaw bark off dogwood trunks. This injury may allow disease organisms to invade the tree. Delay spreading winter mulch over the root zone until the ground freezes, so rodents are forced to nest elsewhere. Keep mulch away from the trunk base and keep the area clear of weeds and grass. If necessary wrap the base of the trunk with a guard of 1/4-inch hardware cloth or other protective wrap made to protect young tree trunks. For more information see the files Dealing With Mice and Dealing With Voles
Bark Of Trunk Rubbed Raw; Tree In Decline Possibly Deer Damage
Deer do not usually seek out dogwoods, but any young, new tree in their browsing range usually invites them to rub the bark with their heads or antlers. Known as ‘buck rub’, this behavior can kill your tree by girdling it. Protect the trunk of any new tree with fencing fastened to two or three poles or other protective tree guards if deer are a problem in your area. For more information see the file Controlling Deer
