Dogwood Leaf Drop: Reasons Why Leaves Are Falling Off Dogwood
By: Bonnie L. Grant, Certified Urban Agriculturist
There are any number of diseases and pests that can stress your dogwood and cause dogwood leaf drop. It is normal to see leaves falling in autumn but you should not see a dogwood tree dropping leaves in summer. When leaves are falling off dogwood in summer, it could mean a serious illness, improper siting or cultivation problems. Let’s examine proper cultivation and conditions for the trees and see what can be done about treating a diseased dogwood.
Why Leaves are Falling Off Dogwood?
Dogwoods are elegant, beautiful ornamental trees with several seasonal displays. Their oval to heart-shaped leaves deepen to crimson and orange in fall. The green leaves add charm and movement during the growing season and set a perfect backdrop for the bright flowerlike bracts. Dogwood leaf drop is not only an unsightly problem but it can spell doom for a plant due to reduced vigor. It is essential to determine the cause and preserve the energy gathering foliage.
Dogwood plants need acidic well-drained soil in full to partial shade. Failure to provide these conditions will encourage disease and pest problems.
Pests That Cause Leaf Drop
Some of the most common pest causes of a dogwood tree dropping leaves are:
- Borer insects
- Dogwood sawfly
Insect pests are usually the easiest to diagnose. Borers leave piles of sawdust near the holes they make, scale is visible as little armored bumps along stems and sawfly larvae cause skeletonized leaves with whitish powder coating them. Borers and scale respond to appropriate insecticides while sawfly larvae are large and obvious enough to hand pick and destroy. Treating a diseased dogwood is a bit harder and requires correct diagnosis of the disease.
Treating Dogwood Leaf Diseases
Diseases of dogwood are the usual suspects when leaves are falling prematurely and include:
- Powdery mildew
- Leaf spot disease
One of the most recurring causes of leaf drop is powdery mildew. Many varieties of plants can get this fungal infection, which cause leaves to get a white coating and eventually suffocate and die. If a tree has a lot of powdery mildew, the overall health of the tree is affected due to minimized harvest of solar energy. Fungicides can be effective or you can prune out the infested areas. If the disease is a common problem in your area, it is best to choose a cultivar with powdery mildew resistance.
Leaf spot disease also occurs on twigs and buds. It causes brownish tan spots on foliage, especially on shaded trees after heavy rains in the warm seasons. Prune out affected stems and leaves and destroy the plant material.
Crown canker is a serious disease that will eventually girdle the tree, causing not only leaf drop but complete die back. The tree will need to be removed and destroyed.
Anthracnose affects many ornamentals. It is characterized by purple spots on bracts and leaves in spring. Usually no treatment is necessary, but in severe cases, use fungicide at bud break. Follow with the spray every 7 to 14 days until all the leaves have opened.
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Prevention of Dogwood Tree Bark Disease
When choosing dogwood for landscaping, be sure the trees are healthy. If any trees are contaminated, they will infect other trees and plants in the landscape. Be sure to select a good site in the yard. The best site promotes rapid drying of foliage and has good-draining soil. The dogwood does not need to be pruned, except in the spring and throughout the growing season to remove dead and decaying wood and plant matter.
- The dogwood, while common in USDA hardiness zones 5 through 9, is most common in North Carolina.
- The dogwood does not need to be pruned, except in the spring and throughout the growing season to remove dead and decaying wood and plant matter.
- Avoid digging native trees from the woods and transplanting them into landscapes. This practice can introduce the disease into a neighborhood that was previously disease free.
- Plant disease-resistant cultivars of flowering dogwoods. Tartarian dogwood (Cornus alba), redosier dogwood (C. sericea), and Cornelian cherry (C. mas) also are resistant to this disease.
Avoid over application of fertilizer which can result in succulent new growth with greater susceptibility to disease.
Prune out all dead or dying twigs and limbs during dry weather. All water sprouts or suckers on trunks and branches should also be removed.
- In the fall, rake and remove fallen leaves. Remove any dead leaves still attached to the branches.
- Registered fungicides can be utilized on trees in landscapes in the spring at bud break, followed by additional sprays every 10-14 days until leaves are fully expanded. Trees should also be sprayed once in the fall after the leaves have changed color, but before leaf drop.
Common flowering dogwood pests and diseases
1 Dogwood anthracnose
This fungal disease can weaken and even kill a dogwood over time. The first symptom is small leaf spots with purple halos, which may expand to form larger tan blotches. Infected leaves will cling to the tree all winter instead of dropping in fall. Dogwood anthracnose may spread to the twigs, larger branches, and trunk, causing dieback. The lower branches will die first.
There are other leaf spot diseases which are merely cosmetic and cause no serious harm, so don’t assume the worst if you see a few spots. Also, dogwood anthracnose is much more common in the wild in cool, moist forests at high altitudes than it is in the typical home landscape, so the situation will not be as dire as it seems in most residential areas.
2 Dogwood borer
This insect is the larva of a moth which burrows into a branch or trunk of a dogwood and feeds under the bark, weakening the tree and sometimes killing it. Borers often gain entrance through a wound in the trunk, such as one caused by a lawnmower. One symptom to watch out for is leaves that start to turn red in summer. You may also see some dieback in the canopy, along with rough bark and frass (caterpillar droppings) at the borer’s point of entry.
3 Powdery mildew
This fungal disease appears as a white coating on dogwood leaves and buds, particularly on newer growth. In a heavy infestation, the leaves are distorted as soon as they emerge. However, powdery mildew isn’t a particularly serious disease, and the damage is mostly cosmetic.
Anthracnose Dogwood Borer Powdery Mildew
Diagnostic Chart of Flowering Dogwood Problems
Browning leaf edges, leaves drooping, wilting
General stress. Peeling, cracked bark near base of tree, brown leaf edges/wilting, purple/red leaf color
Authors: David L. Clement and Mary Kay Malinoski, University of Maryland Extension Specialists. Revised and edited by Christa K. Carignan, Coordinator, University of Maryland Extension Home & Garden Information Center, 12/2019.
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Treating Dogwood Leaf Diseases - Help For A Dogwood Tree Dropping Leaves - garden
In Illinois, we may see three foliar diseases of dogwood. All are fungal diseases: Septoria leaf spot, spot anthracnose, and Discula anthracnose. The first two cause aesthetic problems, but Discula anthracnose can kill branches and even entire trees. Fortunately, we do not see Discula anthracnose often in Illinois landscape settings.
Spot anthracnose occurs in the spring and is caused by a fungus, Elsinoe corni. It affects flowers, leaves, young shoots, and even fruit. The spots are very small (about the size of the head of a pin), purple, and sometimes with a yellow center. Centers often drop out. The spots may merge to cause larger affected areas. This anthracnose disease is similar to those we experience on shade trees. Intensity is definitely related to the amount of moisture in the spring, in this case before or during flowering. Fungicide sprays are available to control this disease but would only be used where the problem is annual. Sprays are applied from bud swell through flowering. In Illinois, sprays are usually not needed. The disease may be severe when spring weather is particularly wet and cool during flowering, but sprays must be initiated before flowering. They work as preventives, not curative applications.
Septoria leaf spot occurs near the end of summer and is visible now in Illinois. It is more common in wet conditions or high humidity. Several Septoria species may infect dogwoods. Purple spots, often with gray centers, occur on the leaves. These spots are larger than those of spot anthracnose, reaching about 1/4 inch in diameter.
Septoria has tiny, submerged fruiting bodies (pycnidia) that can be seen as black specks in the lesions.
Diagnostic spores are found within the fruiting bodies. No cankers are associated with the disease. Supposedly, stressed trees are more susceptible, but that does not always seem to be true on cases we have observed at the Plant Clinic. We do not usually recommend fungicide sprays to protect dogwoods from Septoria in Illinois.
Discula anthracnose appears in Illinois in early summer (June), causing leaf spots similar in size to those of Septoria leaf spot, but without the obvious fruiting bodies. The leaf becomes blighted at the tip and edges.
Lower leaves are affected first. Discula anthracnose also causes stem cankers, killing shoots and contributing to the decline of the tree. Blighted leaves often remain attached to the dead twig, even into autumn. This disease is caused by Discula destructiva, aptly named. It is difficult to manage this disease. Keep dead wood trimmed out of your tree so that cankers do not move into the trunk. Remove the dead wood from the site and burn if possible. Water the soil around dogwoods in drought and use shredded bark mulch over the root system. Keep the mulch off the trunk. Fertilize in the spring or fall with a balanced fertilizer. High nitrogen levels may promote anthracnose. This disease is most likely to appear on trees in shady locations. It can be managed if caught early, before cankers invade large limbs. Many fungicides are registered for use against this pathogen. Sprays are applied in the spring to protect newly emerging leaves. Refer to the Illinois Commercial Landscape and Turfgrass Pest Management Handbook or the Home, Yard, and Garden Pest Guide for registered fungicides.