USDA Forest Service
 

Forest Health Protection, Southern Region

 

USDA Forest Service
Forest Health Protection
Region 8
1720 Peachtree Road, NW
Room 816 N
Atlanta, GA 30309

Phone: (404) 347-7478
Fax: (404) 347-1880

United States Department of Agriculture Forest Service.

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Image of Dogwood

 

Growing and Maintaining Healthy Dogwoods

Also available in PDF format PDF

Contents


INTRODUCTION

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The natural range of dogwoods extends from Maine to the Gulf of Mexico. The trees color cities and countrysides white with dazzling displays in the early spring.

Although they are most spectacular in spring, part of the attraction of dogwoods lies in their year-round beauty. They are truly a four-season plant, displaying rich green luster in the summer followed by deep red leaves in the fall. Bright red clusters of seeds decorate the tree in the winter months.

The native dogwood, Cornus forida, is a small, bushy tree reaching 15 to 30 feet in height. Its short trunk has several large, wide speading branches forming a dense rounded crown. Dogwoods usually grow best in the shade of other hardwoods.

A wide variety of dogwoods is available. The Bay Beauty is more tolerant to drought and heat than are other varieties and can be planted in full sun with better results than the native dogwood. Other cultivars have been developed to highlight different characteristics. Cherokee Chief has deep red flowers while Plena has white semi-double flowers. Rubra is the original pink dogwood, and Fragrant Cloud boasts slightly scented white blossoms. Another dogwood to consider is the Kousa or Japanese dogwood. It is similar to the native dogwood except that it's petal-like flower bracts are pointed (rather than notched), and it blooms from late April through May after full foliage has been attained.

All dogwoods have the potential to flower. The age at which they begin flowering will vary with genetic differences and site conditions. Generally, it takes 3 to 5 years before the first flowers are produced, then flowering recurs almost yearly with a heavy crop about ever other year.

Dogwoods are a valuable and enduring asset to any homeowner's property. This brochure presents the main points to consider when you select your dogwood, and how to maintain it in good health for many years. If you have any questions, contact your local nursery, your State forestry agency or Cooperative Extension Service.


SOURCES OF PLANTS

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Dogwoods grow widely on most sites in the East, if you want additional dogwoods, the source of your new trees will he important in getting and maintaining healthy plants.

Buy your tree from a local nursery. This source ofters you the best prospects for a healthy tree. inspect all trees carefully. Avoid trees with broken or dead branches, trunk damage or leaf spots, all of which indicate unhealthy trees.

Digging plants trom the wild is not a good idea. Wild dogwoods may transmit insects and diseases to healthy trees.


PLANTING SITE

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Dogwoods naturally grow as an understory plant in forests where organic material and natural surface mulch are present. When planted in poorly drained areas, dogwoods do not grow well and may even die, If dogwoods are not properly planted and cared for, they will grow poorly when exposed to full sun. Marginal leaf burn or scorch often result from this condition. Good planting sites should have at least partial shade. Avoid areas where the soil is often wet.

Preparing the planting site properly is extremely important. If this is not done at the outset, then poor growth will result. Dig a hole at least 18 inches deep and 3 feet in diameter, regardless of the tree size. Current research has shown that the addition of soil amendments to the planting hole is unnecessary. In most cases, the soil removed from the planting hole is sufficient for good tree growth.

It is very easy to plant trees too deep. Dogwoods are very shallow-rooted plants, so avoid planting your tree deeper than it grew in the nursery.

Potted or container-grown dogwoods can be planted any time if they are watered regularly. Balland-burlap and bare-root trees should be planted from November through April. Prune off only broken or damaged branches for the first few years so that a good root system can be established.


MAINTENANCE OF ESTABLISHED TREES

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Healthy dogwoods usually result from regular, etfective maintenance programs. Watering, fertilizing, pruning, and mulching are vital components of a good maintenance program.

In the absence of regular rainfall, dogwoods will need supplemental water during the summer and tall, Watering once a week, in the morning, with a soaker hose is recommended for their shallow root systems. The soil should be watered to a depth of 6 inches. Watering with a sprinkler is not recommended because it wets the foliage, creating ideal conditions for certain diseases.

Dogwoods in natural areas usually do not require fertilization. However, trees in yards and restricted growing sites can benefit from a suitable fertilizer. Soil testing is recommended to determine fertility levels and application rates. Broadcast fertilizer on top of the soil. Fertilize trees in late spring or early summer after leaves complete expansion. Never use fertilizers containing weed killer, Always thoroughly water the area after fertilization.

Regular pruning serves many purposes. Removing dead and diseased branches helps prevent the spread of disease and insect pests, Pruning improves the tree's structure as well as its appearance, With a few exceptions, winter is an excellent time to prune your tree.

All pruning cuts should be made with clean, sharp tools and should be properly positioned and made in the proper order. First, locate the tree limb's branch collar (see figure 1). Follow the steps shown for proper pruning cuts. Pruning paint is not needed.


Figure 1. Pruning guide.

Figure 1. Pruning guide. (Click for detail. GIF 6K).


Mulching is one of the easiest and most protective things you can do for your trees. A mulch is used for appearance, weed control, water conservation, erosion control and improvement of soil structure. Mulches also insulate the roots from cold or heat. Apply pine straw or bark 4 to 6 inches deep underneath the limb spread to achieve the above goals. A mulch also reduces the need for mowers and string trimmers next to the trunk, thus reducing injury from these tools.


MECHANICAL INJURY

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A common mechanical injury to dogwoods is caused by lawnmowers hitting the base of the trunk (figure 2). Such injuries invite basal stemrot disease and insect borer infestation. Place a permanent barrier around the trunk to avoid injury.

Figure 2. Lawn mowers and string trimmers cause significant damage.
Figure 2. Lawn mowers and string trimmers cause significant damage. (Click for detail. JPG 31K).


Mulching around the base of the tree discourages weeds and reduces the need to mow close to the trunk. String trimmers pose a similar danger and will bruise or girdle the cambium, the vital layer of tissue under the bark. This damage is not easily detectable until sudden tree decline or leaf drop result.

Dogwoods and other woody ornamental are very susceptible to herbicides. Distorted yellowing leaves can result from herbicide use. Browning or leaf scorch may also be observed (figure 3).

Figure 3. Leafscorch is common on poorly managed dogwoods.
Figure 3. Leafscorch is common on poorly managed dogwoods. (Click for detail. JPG 24K).


Spray equipment that has been used for herbicides should not be used to apply insecticides or fungicides to dogwoods.

In many cases, reduced growth results from chemical damage or mechanical injury. Discolored foliage and scorched leaves are usually followed by branch die-back and eventual death. Periods of stress brought on by drought heighten these symptoms. Identify the problem before attempting to solve it.


DOGWOOD DISEASES

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Dogwood Anthracnose

Dogwood anthracnose causes leaf spots, stem cankers, and kills shoots. Infected trees, if not properly maintained, may decline. This disease should not be confused with spot anthracnose.

Initial symptoms are medium-large, purple-bordered leaf spots, and scorched tan blotches thatmay enlarge to kill the entire leaf (figure 4). Blighted leaves often cling to stems after normal leaf drop in the fall (figure 5). Trunk sprouts occur during the latter stages of disease development. The fungus infects twigs and can grow down a limb and infect the main stem (figure 6). Cankers that form on the main stems can be detected when the bark is peeled back. Cankers are identified by distinct margins surrounded by healthy cambium tissue (figure 7).

Figure 4. Leaf spots on dogwood caused by dogwood anthracnose.
Figure 4. Leaf spots on dogwood caused by dogwood anthracnose. (Click for detail. JPG 27K).


Figure 5. Blighted dogwood leaves cling to branches after infection by dogwood anthracnose.
Figure 5. Blighted dogwood leaves cling to branches after infection by dogwood anthracnose. (Click for detail. JPG 31K).


Figure 6. Dead shoot and stem canker caused by dogwood anthracnose.
Figure 6. Dead shoot and stem canker caused by dogwood anthracnose. (Click for detail. JPG 24K).


Figure 7. Discoloration is evident when bark is cut away from twigs infected with dogwood anthracnose.
Figure 7. Discoloration is evident when bark is cut away from twigs infected with dogwood anthracnose. (Click for detail. JPG 17K).


Dogwood trees that are adjacent to natural stands of dogwoods may be more susceptible. Prune any dead wood in the tree before disease reaches the main trunk. Destroy the pruned wood to eliminate any sources of fungus from the area. Water during droughts, protect the root zone with a mulch and fertilize according to soil analysis. Avoid fertilizers with a high nitrogen content. Fungicides registered for anthracnose on dogwoods can be used. These steps will keep the disease incidence low.

Do not transplant dogwoods into urban areas from trees dug in the woods. You may be transporting the disease into an area where it did not previously occur.

Spot Anthracnose

Flower bracts are usually infected first, but this kind of anthracnose also occurs on leaves, young shoots, and fruit.

The initial symptoms are small, reddish-purple leaf spots that are circular or elongated (figure 8). They are first noticed in early spring. The spots are usually 1/25th inch in diameter (pinhead size). The centers are yellowish, with brown or black margins. As additional infections occur, the spots become numerous and eventually merge, forming larger leaf spots.

Figure 8. Spot Anthracnose causes small, purple-bordered leafspots in the spring and may extend into  the growing season.
Figure 8. Spot Anthracnose causes small, purple-bordered leafspots in the spring and may extend into the growing season. (Click for detail. JPG 25K).


Severely infected flower bracts usually fall from the plant prematurely. Those diseased bracts that do remain on the tree are generally small and distorted. Infection from the bracts then moves to the foliage.

The leaf spots are usually circular, although they may be somewhat angular or elongated. The spot centers are yellow to grayish, with a dark purple border. The centers will eventually drop out. Young shoots and berries may develop elongated, scabby lesions that have a distinct purple border.

Spot anthracnose is caused by the fungus, Elsinoe corni. The fungus persists from year to year in infected twigs, fruit, and other tissues. If the weather is dry before or during the flowering period, very little disease will be observed. Infections will vary from year to year because of this dependency on free moisture.

In most cases, fungicide sprays are not needed, as this disease does not result in significant damage. If fungicides are used, apply them from bud swell through bloom.

Septoria Leaf Spot

The symptoms of septoria leaf spot include medium uniform, purplish spots, or lesions on the leaves. These lesions do not retain the deep, purple border, although the centers of these spots become grayish. This disease occurs near the end of the summer. Stressed or weakened trees are more susceptible than those growing on a natural site, or those in a healthy condition. Septoria leaf spot is generally more of a problem when wet conditions persist and humidity is high.

Botrytis Petal Blight

Botrytis Petal blight is caused by the fungus, Botrytis cinerea. This fungus affects foliage and green shoots as well as petals. Disease is generally observed during wet spring weather, often foIlowing winter injury. The fungus reproduces on diseased tissue during periods of high humidity. Spores are spread by wind and water.

Usually, this disease does not cause significant damage to warrant application of any fungicide. The best disease control is to keep plants healthy with , regular pruning, watering, mulching and fertilization.

Trunk Canker

Basal trunk canker, caused by the fungus, Phytophthora cactorum, is a major problem for urban dogwoods and is generally associated with low, poorly-drained areas. Injuries caused by lawn mowers and insects are ideal sites for fungus infection.

The leaves of infected trees are stunted and generally turn red prematurely. The basal portion of the trunk sinks, causing constriction and decay. The bark eventually peels away, exposing the wood. Some bleeding from the canker can occur, and sprouting may occur below this damaged area. Avoid injury to the tree base, select proper planting sites and control insects to help reduce trunk canker disease.


INSECTS

 

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Insect damage to dogwoods is very common. Most of the damage is considered minor; however, when other stress conditions are present, damage can be significant.

Dogwood Twig Borer and Clubgall Midge

Both of these insects cause tip dieback. Damage usually appears as withering leaves on branch tips during the growing season. For minor infestations prune and destroy dead twigs and branches yearly.

Figure 9. Clubgall midge produces spindle-shaped swellings on the twigs.
Figure 9. Clubgall midge produces spindle-shaped swellings on the twigs. (Click for detail. JPG 18K).


Dogwood Borer

The dogwood borer is a common insect pest on established dogwoods. The larvae of the borer enter the tree through openings in the bark and feed on the cambium layer of the tree. Most attacks occur around basal wounds caused by lawn mowers and string trimmers. The best prevention for this insect is to protect the trees from wounds.



TEN ESSENTIAL STEPS TO MAINTAINING HEALTHY DOGWOODS


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  1. Select healthy trees to plant.
  2. Purchase trees from a reputable nursery; do not transplant trees from the wild.
  3. Select good planting sites to promote rapid foliage drying.
  4. Use proper planting technique
  5. Prune and destroy dead wood and leaves yearly; prune trunk sprouts in the fall.
  6. Water weekly in the morning, during drought. Caution—do not wet foliage.
  7. Maintain a 4- to 6-inch deep mulch around trees; do not use dogwood chips as a mulch.
  8. Fertilize according to soil analysis.
  9. Use proper insecticide and fungicide where appropriate.
  10. Avoid mechanical and chemical injury to trees.


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Prepared by

Kenneth R. Bailey, District Forester
Georgia Forestry Commission

Edward A. Brown II, Plant Pathologist
Cooperative Extension Service,
University of Georgia

USDA Forest Service, Southern Region
1720 Peachtree Road, NW
Atlanta, GA 30367-9102

 

 

This brochure has been published through the cooperative efforts of the following to clarify some dogwood diseases to the public and illustrate the benefits of proper maintenance to growing healthy trees.

  • Carson-Newman College, Jefferson City, TN
  • Champion International Corporation,Stamford, CT
  • Georgia Forestry Commission, Macon, GA
  • Izaak Walton League of America
  • Southern Appalachian Man and the Biosphere, a cooperative of Federal agencies and a nonprofit foundation
  • Southern Nurserymen's Association, Marietta, GA
  • Tennessee Valley Authority
  • U.S. Department of Agriculture, Forest Service, Southern Region
  • University of Georgia, Cooperative Extension Service, Athens, GA
  • Your local nursery professional

ACKNOWLEDGMENTS

 

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The authors acknowledge the review of this manuscript by H. Daniel Brown - USDA Forest Service, Atlanta, GA; Robert L. Anderson - USDA Forest Service, Asheville, NC; Dr. R.W. Roncadori - Plant Pathologist, University of Georgia; Dr. Floyd Hendrix - Plant Pathologist, University of Georgia; Dr. Kim D. Coder, Extension Forester, University of Georgia.

April 1989, revised March 1991


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USDA Forest Service - Forest Health Protection, Southern Region
Last Modified: Monday, 16 December 2013 at 14:18:29 CST


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