Miscellaneous

Dogwood Anthracnose – Information About Dogwood Blight Control

Dogwood Anthracnose – Information About Dogwood Blight Control


By: Kristi Waterworth

Dogwood trees are beautiful, iconic landscaping trees that come from the forest understory. Although they’re great for adding lots of curb appeal, they’ve got a few serious problems that can spoil the idyllic feel of your yard. It’s never good news when a tree gets sick, especially when it’s your stately dogwood tree. Dogwood tree blight, for example, is a fungal infection of dogwood trees that can turn these valuable visual assets into serious detriments. Read on to find out about dogwood tree blight and what you can do to help your plant through this rough time.

Dogwood Anthracnose Information

Dogwood blight, also known as dogwood anthracnose for the fungal pathogen that causes the disease, is a fairly new problem. It is believed to have started in the northeastern United States about 25 years ago, but has been spreading southward ever since.

The early symptoms are similar to leaf spot diseases, with purple bordered soft wet spots appearing on leaves, especially around the margins. Once the disease spreads to leaf petioles and twigs, however, it becomes more obvious. Leaves attached to these infected areas will shrivel and turn black. In very advanced disease, lower branches may die, cankers may form on the limbs, and trunk sprouts will increase in number.

Controlling Dogwood Blight

Dogwood blight control is difficult, but if you catch it early, you may be able to save the tree by cutting out all diseased tissues. That means all leaves, all twigs, and all branches showing signs of infection must be removed and destroyed promptly. Small trees may be saved with a fungicide spray applied every 10 to 14 days as long as cool, moist weather persists.

Prevention of dogwood blight is the best tool you’ve got to keep your landscaping trees healthy. Keeping your dogwood properly watered and fertilized is the first line of defense, two to four inches (5-10 cm.) of mulch spread over the root zone will help maintain soil moisture. Removing spent leaves, pruning low branches, opening up a dense canopy, and trimming water sprouts in the fall will create intolerable conditions for the fungus.

If you’ve lost a tree to dogwood blight, consider replacing it with Oriental dogwood (Cornus kousa). It has a high tolerance to anthracnose. White dogwoods seem to be less susceptible to the infection than their pink counterparts. There are also new cultivars of the Appalachian dogwood series that are bred to be anthracnose resistant. Whatever you do, don’t transplant a wild dogwood into the landscape–as this is how many infections started.

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Out My Backdoor: Dogwood Berries Are a Wildlife Favorite

By Terry W. Johnson, writer of the Backyard Wildlife Connection blog. Featured image: Flowering Dogwood Berries. Photo credit: Terry W. Johnson

What would you say if I told you there is a native tree that produces a bounty of colorful berries that are relished by a host of songbirds and other backyard wildlife, and that this tree is as beautiful in a yard as it is in Georgia’s woodlands?

Chances are you would tell me that there is no such tree. Well, actually there is. And it’s a tree that is familiar to Georgians: the flowering dogwood.


How to Treat Twig Blight on Variegated Dogwood Plants

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Any disease that causes cankers and growths on the leaves and twigs of plants is referred to as “blight.” In variegated dogwood trees (Cornus alba) and other dogwoods (Cornus spp.), twig blight is usually caused by the Discula destructiva fungus, but other fungi can also cause infection. Variegated dogwoods grow in U.S. Department of Agriculture plant hardiness zones 2 through 8. Although the twig blight, or dogwood anthracnose, can develop anywhere, it is more likely to occur in USDA zones 7b and above. Twig blight is also more likely during very wet, rainy springs and summers. Trees typically survive twig blights, but the problem can be lethal if allowed to go unchecked during several consecutive wet seasons.

Maintain a vigorous and healthy tree by providing regular care and attention. Keep mowers and trimmers well away from the tree. Spread mulch 2 to 4 inches deep in a 3-foot radius around the tree, and fertilize as needed based on the results of soil testing. Remember to leave a space between the trunk and the mulch, and avoid mulches made from other dogwood trees as these may harbor fungi.

Water the dogwood once a week during periods of drought, watering in the morning and soaking the soil to a depth of 10 to 14 inches. Water stress makes plants more susceptible to twig blight.

Rake up and remove any fallen leaves and other debris each fall so that fungi have no place to conveniently overwinter.

Prune away any limbs affected by twig or leaf blights during your annual winter pruning. Burn or throw away infected limbs do not use them for composting or allow them to sit on your property.

Spray the dogwood with a general purpose fungicide as soon as buds open in the spring. Chlorothalonil is readily available for use in home gardens and is effective against twig blight. Reapply the fungicide every two weeks until the new growth matures. This typically works out to three treatments. More treatments can be applied if rainy weather persists throughout the summer and the tree’s leaves do not have time to dry before nightfall.


ALTERNATE-LEAF DOGWOOD - CORNUS ALTERNIFOLIA

Common Name: Alternate-leaf dogwood, pagoda dogwood

Scientific Name:
Family: Cornaceae
Genus: Cornus
Species: alternifolia

Hardiness Zone: 3 to 7
Height: 15 to 25 ft
Width: 20 to 30 ft

Common Characteristics:

Alternate leaf dogwood is also known as pagoda dogwood for its tiered horizontal branching. Its green, red, or purple branches form a distinctive flat-topped crown accompanied by a spreading horizontal branch architecture. The older parts of the plant, such as the trunk, are mostly smooth and light brownish-green. Its flowers are fragrant and light yellow to cream-colored and bloom in late spring. After flowering, the dogwood will produce pea-sized fruits in clusters that are either green or bluish-black depending on the time of year. The buds of the plant, alternately arranged, are purple and slightly fuzzy/hairy.

Where It Grows:

It is in deciduous and mixed forests where it inhabits understory and border areas. It is also said to inhabit floodplains, cedar swamps, and the banks and thickets above lakes and streams (Schultz). It happily grows in shaded and partially shaded areas in moist, well-drained acidic soil, though it will tolerate a range of soil conditions.

How It's Used:

It is used as an ornamental shrub or small tree. It is an effective border shrub, woodland gardens shrub, and in naturalized areas as a flowering tree (Missouri Botanical Garden).

Ecosystem Services:

The flowers are a nectar source for the Spring Azure butterfly (Celastrina ladon) which also utilizes the plant's flower buds as a host site for its larva (BAMONA). The fruit is bitter and enjoyed by a variety of native wildlife such as birds, bears, squirrels, pheasants, wild turkey, and grouse.

Where It Is Native To:

The native distribution of the plant is mainly in the northeastern and upper midwestern United States stretching north into southern Canada.

Known Varieties and Their Traits:

  • Gold Buillion TM Pagoda dogwood (Cornus alternifolia 'Bachone') - exhibits golden-yellow foliage and plants reach 8 to 10 feet high and wide (Morton Arboretum)
  • Golden Shadows TM Pagoda dogwood (Cornus alternifolia 'W. Stackman') - exhibits a variegated form with creamy-white margins and grows best in partial shade (Morton Arboretum)

This plant is susceptible to leaf spot, twig blight, leaf blight, root rot, golden stem cankers, scale, leaf miner, and borers (Missouri Botanical Garden).

Other Details:

​This species is propagated by seed or softwood cuttings. Cuttings will be most successful if left undisturbed through a winter dormancy period. If propagating by seed, a 2-3 month cold stratification is recommended after removal of the fleshy seed coat (Schultz).

References:
BAMONA (Butterflies and Moths of North America) Found Online:

Missouri Botanical Garden (Plant Finder) Found Online:

Morton Arboretum (Trees & Plants) Found Online:

Schultz, Jan. USDA Forest Service. Found Online:


Prevention

After you have eliminated Dogwood from your property, you will need to put into place preventative measures to make it so Dogwood or any other invasive tree species doesn't reinvade.

  • To prevent Dogwood from regrowing, address soil moisture issues by improving drainage and other routine maintenance tasks to make the environment less conducive to Dogwood tree establishment.
  • Mow your yard at an optimum height of 3 to 4 inches to improve root growth.
  • Apply fertilizer at the best times (ideally in the fall) for your lawn to keep your desired turf thick and lush so Dogwood or other invasive plants don't have an opportunity to take over.
  • Water the grass deeply yet infrequently. We recommend once a week at a rate of 1 to 1.5 inches of water.
  • Rake and dethatch your lawn to allow for better aeration of your lawn as well as address issues like soil compaction and poor drainage.


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