ANR-0551 Dogwood Diseases in Alabama
Dogwood Diseases in Alabama
ANR-0551, Reprinted June 2006. Austin Hagan, Extension Plant Pathologist, Professor, and Jackie Mullen, Extension Plant Pathologist and Diagnostician, both in Entomology and Plant Pathology, Auburn University.
 ogwood is among the most widely grown native trees in home, recreational, and commercial landscapes in Alabama. Dogwood is popular not only for its showy, early spring display of colorful blooms, but also for its widespread adaptability and hardiness across the state. The flowering dogwood, Cornus florida, of which numerous cultivars with varying bract colors and growth habits are available, is the most popular dogwood. The later flowering kousa dogwood, Cornus kousa, is also widely cultivated. Several other dogwood species are available but rarely seen in Alabama landscapes.
Of the cultivated dogwoods, the flowering dogwood suffers from the widest range of foliar and soil-borne diseases. These diseases can greatly reduce the floral display and foliage quality as well as adversely affect the health of the tree. Establishment of dogwood on adapted sites and good maintenance practices often will minimize the effects of environmental stresses that predispose the tree to disease. Also, proper growing conditions will often allow plant recovery from disease-related injury.
This publication describes the following diseases on dogwood as well as recommended control practices for trees in Alabama and neighboring states: spot anthracnose, septoria and cercospora leaf spot, phytophthora crown canker, phytophthora leaf and shoot blight, armillaria root rot, discula anthracnose, and powdery mildew, plus canker, virus diseases, and decline.
Spot Anthracnose
Spot anthracnose, caused by the fungus Elsinoe corni, is the most common foliage disease on flowering dogwood. Although all flowering dogwoods are susceptible to this disease, white cultivars are usually affected most.
Spot anthracnose is particularly common on white seedling dogwoods produced in container and field nurseries, but it is also widespread on trees in home landscapes as well. A similar disease caused by the fungus Asochyta cornicola (Phyllosticta cornicola) is also reported on the flowering and kousa dogwoods.
During periods of wet, humid weather in late winter to early spring, spores produced in fungal fruiting bodies (acervuli) on infected twigs, fruits, and other tissues are spread by windblown rain or splashing
water. Diseased flower buds may be stunted and malformed with some bud death in severe cases.
Spots on the bracts and leaves
are small (usually 1/16 to 1/25 inch diameter), circular to elongated,
with a reddish-purple margin and dusty yellow to tan center. Spots developing on young leaves may
have a yellow halo while those on the mature leaves do not. Heavily spotted bracts and leaves are often badly malformed and distorted, possibly with some reduction in size. Numerous spots may coalesce into large blighted areas.
On young shoots and berries, the disease appears as elongated lesions with purple margins. Lesions may be flat, slightly elevated, or depressed and sometimes scabby. Severely infected berries may be deformed. Badly diseased bracts and sometimes leaves are shed by the tree. As with other foliar tree diseases, spot anthracnose rarely directly kills a tree, although repeated early defoliation may reduce flower bud number and possibly increase plant sensitivity to moisture or temperature extremes.
Frequent rains or extended periods of high humidity are needed for spot anthracnose development. With dry weather during flower bud swell and bloom, symptoms are rarely seen on the bracts. If spotting does not appear on the bracts, the disease may not be severe on the leaves.
In nurseries, the occurrence of spot anthracnose may be reduced by propagating seed or cuttings from symptomless trees and watering with overhead sprinklers in late morning to early afternoon so the foliage dries quickly.
Spot anthracnose is much worse on flowering dogwoods growing in full sun than in shade. Planting new dogwoods, especially early flowering cultivars, on shaded sites often will prevent disease development. Also, early flowering dogwood cultivars such as 'Cherokee Daybreak', 'Cherokee Princess', 'Ozark Spring', 'Springtime', 'Cloud' and 'Barton White' as well as the native flowering dogwoods found in many Alabama landscapes are very susceptible to spot anthracnose. On sunny sites, outbreaks of spot anthracnose can be largely avoided by planting a late flowering dogwood cultivar such as 'Welch's Bay Beauty', 'Cherokee Chief', 'Cherokee Sunset', 'Weaver's White', 'Pink Rubra', 'Junior Miss', 'Cherokee Brave', 'Double
White' ('Plena'), or 'Red Beauty'.
In landscapes, applying a fungicide (see Table 1) every 7 to 10 days starting at bud break through bract fall will control spot anthracnose. In nurseries, apply protective fungicides beginning at bud break until all new growth matures. See Extension publication ANR-0941, "Spot Anthracnose on Flowering Dogwood," for more information.
Table 1. Chemical Control of Spot Anthracnose
| Fungicide |
Rate |
Comments |
| Per gal |
Per 100 gal |
| azoxystrobin |
Foliar Spray:
Make first application when flower buds show color and repeat every 7 to 14 days until the bracts fall.
On badly diseased trees, continue fungicide applications until the new leaves mature in mid-June.
Refer to label for the recommended application interval for each fungicide. |
| Heritage 50W |
— |
4 to 8 oz |
| chlorothalonil |
| Daconil Ultrex |
— |
1.4 lb |
| Daconil WeatherStik 6F |
— . |
1 3/8 pt |
| Garden Fungicide |
2 ¼ t. |
— |
| myclobutanil |
| Immunox |
2 T. |
— |
| Eagle 40W |
— |
3 to 6 oz |
| tebuconazole |
| Disease Control for Roses, Flowers, and Shrubs |
1.5 T. |
— |
| thiophanate-methyl |
| 3336 50W |
2 ½ t. |
12 to 16 oz |
| 3336 4.5F |
1 T. |
10 to 20 fl oz |
| Halt 50W |
2 ½ t. |
— |
| thiophanate-methyl + mancozeb |
Cercospora and Septoria Leaf Spot
Leaf spot diseases caused by the fungi Septoria spp. and Cercospora cornicola may appear on flowering dogwood anytime from midsummer to early fall following several days of showers. The light spotting of the leaves has little impact on tree health, but repeated defoliation over several years may reduce tree vigor. Leaf spot damaged flowering dogwoods that lose their leaves in 2 to 3 weeks have little fall color. Septoria leaf spot is also reported on the redosier dogwood (C. stolonifera). Of these
two diseases, cercospora leaf spot is most common.
Cercospora leaf spots are angular to irregularly
shaped and tan-brown areas (1/8 to 1/4 inch diameter) with diffuse borders. Following a heavy dew or rain shower, numerous dark tufts of the spore-producing structures (conidiophores) can be seen with a hand lens on the upper surface of the leaf spot.
Septoria leaf spot is very similar in appearance and size (1/8 to 1/4 inch diameter) to cercospora leaf spot. Initially, the spots are angular to irregular in shape, usually bordered by the leaf veins, and dark brown-purple in color; later, they develop light brown or gray centers with dark borders. Heavily spotted leaves may be shed early.
Damage to the fruit appears as a distortion or roughening of the seed coat. Septoria spp. produce numerous spores in hard to find fruiting bodies (pycnidia) embedded in the dead tissues within leaf spots.
Both cercospora and septoria fungi over-winter in diseased leaves on the ground or hanging on the tree. During wet weather, spores will infect leaves, particularly those in the lower portions of the tree canopy. Both diseases will intensify during favorable weather from July until November.
Specific control measures for cercospora and septoria leaf spots on flowering dogwood have not been developed. Good tree management practices should prevent a serious reduction in plant vigor resulting from early leaf drop. Fungicides should provide good protection from both diseases. Apply a recommended fungicide (see Table 2) several times at 10- to 14-day intervals shortly after an extended
period of rain starting in July or August. Protective applications are suggested only on trees damaged nearly every year by either of these diseases.
Table 2. Chemical Control of Cercospora and Septoria Leaf Spot
| Fungicide |
Rate |
Comments |
| Per gal |
Per 100 gal |
| azoxystrobin |
Foliar Spray:
Apply at first sign of disease on leaves in late July to early August.
Repeat fungicide applications at 10- to 14-day intervals until late September to early October.
The application interval for Heritage 50W is 14 to 28 days. |
| Heritage 50W |
— |
1 to 4 oz |
| Chlorothalonil |
| Daconil Ultrex |
— |
1.4 lb |
| Daconil WeatherStik 6F |
— . |
1 3/8 pt |
| Garden Fungicide |
2 ¼ t. |
— |
| Myclobutanil |
| Immunox |
2 T. |
— |
| Eagle 40W |
— |
3 to 6 oz |
| Tebuconazole |
| Disease Control for Roses, Flowers, and Shrubs |
1.5 T. |
— |
| thiophanate-methyl |
| 3336 50W |
2 ½ t. |
12 to 16 oz |
| 3336 4.5F |
1 T. |
10 to 20 fl oz |
| Halt 50W |
2 ½ t. |
— |
Phytophthora Crown Canker
Crown canker caused by the soil-borne fungus Phytophthora cactorum is a destructive disease of flowering dogwood in the home landscape and field plantings in commercial nurseries. The disease usually develops on newly transplanted trees or those that have suffered injury to their roots. Dogwoods with low vigor, especially those grown on poorly drained or wet sites, are more sensitive to crown canker; however, healthy trees may also be attacked by the crown canker fungus.
A root rot disease that may be caused by the crown canker fungus or Phytophthora cinnamomi is also found on field or container-grown dogwood grown in poorly drained soils or potting mixes.
Crown canker usually is first apparent when leaf number and size are greatly reduced. Leaves on diseased
trees are small with a pale yellow-green to red color in late summer; they bend downward from the petiole, and fold along the midrib, and they may shed early. Wilting and leaf edge browning, symptoms usually associated with drought, appear earlier on diseased dogwood than neighboring healthy trees.
A slow dieback of twigs and branches along with the production of unusually large flowers and a heavy fruit
set is often seen on diseased trees just before their death. Diseased dogwood may die in 1 to 2 years or they may linger with little growth or vigor for several years. Foliar symptoms of root rot caused by P. cinnamomi are similar to those of crown canker.
A slow-developing canker on the lower trunk near the ground line is characteristic of crown canker on dogwood. During early stages of the disease, the cankers may not be apparent except for the oozing of dark-colored fluid from the bark at the soil line. By removing the outer bark, the typical browning of the inner bark, cambium, and sapwood can easily be seen. Over a period of months to years, the canker face becomes cracked and sunken, and it dries and falls away, exposing the heartwood. As a diseased dogwood weakens, it is more susceptible to dogwood borer or environmental stresses that often kill the tree.
Because the disease is associated with wounding of the roots and crown, care should be taken when transplanting, cultivating, or weeding to avoid injuring the crown and roots of dogwood. Any bark damage may be quickly colonized by either the crown canker fungus or dogwood borer. Disease incidence is usually lowest on well-drained, slightly acid sites. Amending soil from the potting hole with pine bark to a depth of 8 to 12 inches is suggested. Container-grown dogwood should be produced in a fast-draining soilless potting medium on crowned beds to minimize water retention and reduce phytophthora
crown canker and root rot.
In home landscapes and production fields, diseased dogwood should be removed and replaced with a woody ornamental resistant to Phytophthora spp. In container nurseries, contaminated potting media should be discarded and all flats, used containers, benches, and propagation tools should be
soaked in a surface disinfectant such as a denatured alcohol or a germicidal soap. Fumigation
of infested beds with metamsodium (Vapam) will reduce but not eliminate the fungus in the soil. Further information on soil fumigation is discussed in Extension publication ANR-0030, “Nematode Control in the Home Garden.”
Fungicide drenches will provide some protection from phytophthora crown canker and root rot on container- and field-grown dogwood, but such treatments are not practical in the home landscape. Combined with good production practices and crop sanitation, fungicide treatments (Table 3) applied through the production cycle at intervals specified on the product label will control this disease.
Curative treatments applied after the pathogens have become established are not effective.
Table 3. Control of Phytophthora Collar and Root Rot
| Fungicide |
Rate |
Comments |
| Per gal |
Per 100 gal |
| fosetyl-Al |
| Aliette 80WDG |
— |
8 to 12.8 oz |
Dry Soil Mixture: Use on well-rooted plants. Thoroughly incorporate fungicide into potting medium before planting or stepping up liners and container material. Begin protective soil
drenches or spray 1 month after treatment. |
| — |
6.4 to 12.8 oz |
Drench: Apply 2.0 quarts of fungicide suspension per square foot of bed area. Repeat as needed but do not exceed one application every 30 days. |
| — . |
2.5 to 5.0 lb |
Foliar Spray: Apply as needed but do not exceed one application every 30 days. Do
not mix with sticker, extended, or wetting agent. |
| Mefenoxam |
| Subdue Maxx |
— |
1 to 2 fl oz |
Soil Drench: Apply 1½ to 2 pints of drench solution per plant
treated at 2- to 3-month intervals. |
| Subdue GR |
— |
26 to 125 oz |
Broadcast: Apply to 1,000-square-foot area and thoroughly wet soil. Repeat application
every 2 to 4 months as needed. |
| Propamocarb |
| Banol 67S |
1.5 T. |
25 fl oz |
Soil Drench: Apply 5 quarts of drench solution to a 10-square-foot area. Repeat every 3 to
4 months as needed to control disease. |
Phytophthora Leaf and Shoot Blight
Phytophthora leaf and shoot blight occurs primarily on container-grown flowering dogwood in nurseries along the Florida and Alabama Gulf Coast. The causal fungi Phytophthora parasitica and P. palmivora are most aggressive on flowering dogwood during extended periods of hot, wet weather in June, July, and August. If considerable shoot blighting occurs, diseased flowering dogwoods are not marketable. All cultivars of flowering dogwood appear to be susceptible to Phytophthora leaf and shoot blight.
Randomly scattered gray-green, water-soaked spots on the leaves are the first noticeable symptoms of
Phytophthora leaf and shoot blight. These spots quickly expand into large, irregular brown blotches with a graygreen border that eventually cover the entire leaf. Under hot, wet conditions, these blighted leaves quickly wither and die. The fungus will then invade, girdle, and kill the leaf-bearing shoots. The dead leaves are not shed in the fall but may remain on the plant until the next spring.
Spacing out container-grown flowering dogwood may slow tree-to-tree spread of Phytophthora leaf and shoot blight. During the summer, blocks of flowering dogwood should be inspected weekly for symptoms and badly diseased trees should be discarded. When using overhead sprinklers, water flowering dogwood between 2 and 6 a.m. or at mid-day. Watering in late afternoon or early evening, especially on cloudy
days before or after a shower will greatly increase the risk of disease development. Recycled water
must be filtered and sterilized or chlorinated before being applied to nursery stock.
Flowering dogwood can be protected from Phytophthora leaf and shoot blight with the fungicide listed in Table 4. Inspect blocks of containergrown flowering dogwood weekly and begin fungicide applications when symptoms first appear. Continue applications at the interval specified for each fungicide until weather pattern no longer favors disease development. An alternative would be to begin making protective fungicide treatments in mid to late May and continue treating the trees until weather patterns become cooler and drier in mid-September.
Armillaria Root Rot
Armillaria root rot, otherwise known as mushroom root rot or shoestring root rot, is occasionally seen on
dogwood. The causal fungus, Armillaria tabescens (A. mellea), usually is found in landscape sites where oaks or other hardwoods once were or are now established. Many woody plants, such as dogwood, photinia, arborvitae, camellia, elm, grape, loquat, southern magnolia, silver maple, Russian olive, pittosporum, loblolly pine, and several oaks including laurel, post, red, turkey, water, and
willow are hosts of this fungus.
The ability of Armillaria to attack plants depends largely on the health of the tree or shrub host. Tree and shrub roots weakened by drought are readily colonized by the Armillaria fungus. Reports indicate that insect or disease defoliation, mechanical (construction) injury, and air pollution may also increase plant susceptibility to attack by A. tabescens.
Root rot may appear on one or more dogwood in a given site. Yellowing, sparse foliage, slowed top growth,
shoot dieback, and defoliation are early root rot symptoms. Distinct semi-circular, sunken lesions with a cracked margin may be seen at or just above the soil line of trees and shrubs with a thin bark. Small trees often succumb suddenly to this disease while some trees can withstand severe damage for years.
A white fan-like mat of fungal mycelia under the bark is diagnostic for mushroom root rot. These mats are often seen at or just above the soil line, but they may extend several feet up the trunk. Branched, string-like, brown to black structures called rhizomorphs often are found growing on the surface of the roots, root collar, and into the soil surrounding the affected plants. Flattened rhizomorphs may also form under the root and root collar bark.
Mushrooms are produced on or near the roots of diseased plants in clusters of several to 100. The common
name, honey fungus, refers to the honey-colored cap of the armillaria mushrooms.
Mushrooms usually appear in the fall up to early winter. Dry fall weather often delays mushroom formation
until the following year. Mushroom root rot fungi persist as mycelia in diseased roots and rhizomorphs. Tree stumps are particularly important survival sites and food bases for the fungus in both landscape and orchard settings. The rhizomorphs grow through the soil to the roots of nearby trees and shrubs. Infection of the roots usually occurs after stress. Airborne spores produced in the mushrooms have limited impact on disease spread, although colonization of freshly cut tree stumps is reported.
Good tree vigor is the best defense against armillaria root rot. Recommended fertilization and watering practices should be followed to promote tree vigor and reduce the effect of environmental stresses. Dogwood should be established on sites best adapted for good tree growth. Uprooting stumps and root remnants is recommended as a means of slowing disease spread to nearby healthy trees. Several trees resistant to armillaria root rot are available for establishment on infested sites. See Extension publication
ANR-907, "Armillaria Root Rot of Trees and Shrubs," for more information.
Discula Anthracnose
First reported on flowering dogwood (Cornus florida) in New York and on Pacific dogwood (Cornus nuttallii) in Washington in the mid- to late 1970s, discula anthracnose caused by the fungus Discula sp. has spread into northern Georgia, eastern Tennessee, and into northeastern
Alabama, resulting in the loss of numerous flowering dogwoods. The worst tree decline and mortality in Alabama occurred on forested sites in Calhoun, Cherokee, Cleburne, DeKalb, Jackson, Madison, and Marshall counties particularly at elevations above 1,200 feet. Some damage but no tree death has been noted in this area in home landscapes. In the southeastern states, this disease occurs primarily in
forest settings, but it also may be seen in landscape plantings. Despite the unknown origin of this disease, it has quickly become the predominant disease in native stands of dogwood along the Atlantic seaboard.
The first symptoms occur on bracts when rainy conditions occur during flowering or on leaves in the lower
canopy of the tree. Spots on the bracts are similar to those of spot anthracnose. Tan spots with purple margins (1/16- to 1/4-inch diameter) appear on the leaves. Black or brown discoloration of the veins and leaf margins and large brown blotches may also be seen. Tiny red to dark brown fruiting bodies (condiomata) often develop within the leaf spots or blotches.
During humid weather, white to orangy brown spore masses exude from the red-brown fruiting bodies. Shot
holes may appear where the center of the spot has disintegrated. The blighted leaves are not shed but remain on the tree into the following spring.
In the spring, shoots may be invaded by the fungus through cracks or wounds, forming small cankers that
may encircle (girdle) the stem and result in twig dieback. A purple margin or zone often marks the boundary between the healthy and infected tissues. Several years after the first symptoms, brown, elliptical cankers form on main branches and the trunk at the base of dead twigs. Bark splitting and swellings with some discoloration of the underlying tissues may be associated with the trunk cankers.
Multiple branch and trunk cankers can kill the entire tree. On dying trees, numerous succulent water sprouts (epicormic shoots), which usually are quickly infected, appear on the lower branches or trunk.
Generally, this disease begins in the lower limbs and gradually moves up through the tree canopy. Each spring numerous spores are produced on diseased leaves as well as some blighted twigs. These spores are spread to healthy leaves and shoots by wind-blown rain. Cool, wet springand fall weather favors discula anthracnose, but disease development has been seen throughout the growing season. Dogwoods weakened by drought or temperature extremes may be more susceptible to this disease.
Nearly all native selections and most cultivars of the flowering dogwood (Cornus florida) and Pacific dogwood (C. nuttalli) are susceptible to discula anthracnose. The flowering dogwood 'Appalachian Spring' is highly resistant to dogwood anthracnose. The redosier dogwood (C. sericea)
cultivars 'Kelseyi' and 'Flaviramea,' along with the kousa dogwood (C. kousa) cv. 'Chinensis,' and Tatarian dogwood (C. alba) cv. 'Elegantissma Variegator,' are also susceptible to this disease. The hybrid dogwood (C. florida x kousa) selections 'Stardust,' 'Stellar Pink,' and 'Celestial,' along with the kousa dogwood cultivars 'Steeply' and 'Milky Way,' have good resistance to discula anthracnose. Kousa dogwood cultivars with intermediate disease resistance include 'Milky Way Select,' 'Gay Head,' 'Julian,' 'Temple Jewel,' and 'Elizabeth Lustgarten.' The hybrid dogwood 'Consellation' also has
some resistance to discula anthracnose. Some other discula anthracnose-resistant dogwood including several selections of the Corneliancherry dogwood (C. mas), silky dogwood (C. amonum), C. augustata, redosier dogwood (C. sericea) 'Ruby,' and pagoda dogwood (C. alternifolia).
Discula anthracnose is much more damaging to flowering dogwood grown under heavy shade than those trees found in partial shade to full sun. In areas of northeast Alabama where this disease is common, plant new flowering dogwoods or other susceptible dogwood selections in partial shade, especially those areas that get plenty of morning sun, to full sun. On heavily shaded sites in this same area, plant only disease resistant selections of the kousa dogwood, hybrid dogwood (C. kousa x florida), or
other dogwood species.
Following recommended management and watering practices will lessen the impact of discula anthracnose
on tree health. Dogwoods should be fertilized according to soil test recommendations and surface watered during extended periods of hot, dry weather. Mulching around the tree will reduce water needs and minimize the risk of mechanical damage from mowers or trimmers. Selective pruning of overhanging branches on trees surrounding established dogwoods increases air circulation and sunlight penetration, which speeds the evaporation of moisture or dew from the foliage, thereby creating an environment less favorable for disease development. In addition, blighted twigs should be removed and discarded off-site before cankers develop on the branches or trunk. Fallen leaves from diseased trees also should be collected and discarded.
Fungicides, which will protect susceptible dogwoods from discula anthracnose, are recommended only on those heavily shaded sites where the trees have been previously damaged by this disease. For effective disease control, apply a fungicide (see Table 4) beginning at bud break until the leaves mature every 7 to 14 days. For optimum protection of valuable specimen dogwoods in heavily infested areas of northeast Alabama, applications of a recommended fungicide may be continued through the growing season until frost.
Table 4. Control of Phytophthora Leaf and Shoot Blight
| Fungicide |
Rate |
Comments |
| Per gal |
Per 100 gal |
| azoxystrobin |
Foliar Spray: Apply every 14 to 28 days when conditions favor disease. Occurs
during extended periods of hot, wet weather in July and August on containergrown dogwood. |
| Heritage 50W |
— |
1 to 4 oz |
| chlorothalonil |
Foliar Spray:
Apply every 7 to 14 days when conditions favor disease. |
| Daconil Ultrex |
— |
1.4 lb |
| Daconil WeatherStik 6F |
— |
13/8 pt |
| Garden Fungicide |
2¼ t. |
— |
|
| fosetyl-Al |
Foliar Spray: Apply as needed but do not exceed one application every 30 days. Do not mix with sticker, extended, or wetting agent. |
| Aliette 80WDG |
— |
2.5 to 5.0 lb |
Powdery Mildew
Powdery mildew is the most widespread disease of flowering dogwood (Cornus florida) in Alabama and surrounding states. The powdery mildew fungus (Oidium sp.) has been equally damaging to dogwoods growing on heavily shaded sites to those found in full sun. Although the blemished foliage of diseased dogwoods is unsightly, powdery mildew may have little if any effect on the vigor of established flowering dogwood. However, noticeable stunting and occasionally death have been observed in seedling flowering dogwood.
Small, faint white patches of the thread-like hyphae of the powdery mildew fungus first appear in late spring to early summer on the upper surface of expanding and mature leaves. On susceptible dogwoods, the surface of numerous leaves may be covered with white, cottony fungal growth. Such heavily colonized leaves usually are twisted or distorted. On disease-resistant dogwoods, a few, scattered colonies of the causal fungus usually will not blemish the leaves. Symptoms may continue to appear on new growth throughout the summer and into early fall.
Disease resistant cultivars offer the best long-term control for powdery mildew on dogwood. Of all commonly cultivated species of dogwood, the flowering dogwood (C. florida) is most susceptible to powdery mildew. Susceptibility of individual native flowering dogwoods does considerably differ; trees with severely distorted foliage are often found adjacent to dogwoods with little or no apparent symptoms. When transplanting native dogwoods from wooded areas into home landscapes, only dig trees with healthy foliage. The flowering dogwood cultivars 'Cherokee Brave', 'Jean's Appalachian Snow', and 'Karen's
Appalachian Blush' have excellent resistance to powdery mildew. Moderately resistant cultivars include 'Barton White', 'Cherokee Chief', 'Cloud 9', 'Double White', 'Weaver's White', and 'Welch's Bay Beauty'. Moderate to severe mildew infestations were seen on a number of widely available cultivars of flowering dogwood such as 'Cherokee Sunset', 'Dwarf White', 'First Lady', 'Junior Miss', 'Ozark Spring', 'Pink Beauty', 'Purple Glory', 'Red Beauty', 'Pink Rubra', and 'Stoke's Pink'.
Several kousa dogwood (C. kousa) cultivars also are resistant to powdery mildew. In recent field trials, the kousa dogwood cultivars 'Milky Way,' 'Milky Way Select,' and 'National' have remained nearly free of disease symptoms. In addition, the cultivars 'Gay Head,' 'Julian,' 'Temple Jewel,' 'Big Apple,' 'Greensleeves,' and 'China Girl' along with the recently released hybrid dogwoods 'Stellar Pink,' 'Star Dust,' 'Galaxy,' 'Aurora,' and 'Constellation' have also been shown to have good disease resistance. The giant dogwood (C. controversa) may be immune to powdery mildew.
In the landscape, fungicides can be used to control powdery mildew on established flowering dogwoods.
Fungicide applications are suggested only on valued specimen trees that have previously been damaged by this disease. As the trees leaf out in the spring, inspect the foliage weekly for disease symptoms. Apply a recommended fungicide (see Table 5) when the characteristic fungal colonies or distortion of the new leaves are first noticed. Reapply the fungicide every 7 to 14 days until the leaves have matured or conditions no longer favor disease spread. See Extension publication ANR-1051, "Powdery Mildew
on Flowering Dogwood," for more information.
Table 5. Chemical Control of Dogwood Anthracnose
| Fungicide |
Rate |
Comments |
| Per gal |
Per 100 gal |
| azoxystrobin |
Foliar Spray: Apply at first sign of disease and repeat applications every 14 to 28 days until the new leaves mature. |
| Heritage 50W |
— |
1 to 4 oz |
| chlorothalonil |
Foliar Spray: Begin applications at bud break or at the
first sign of the disease and repeat at 7- to 14-day intervals until the new leaves mature. The application interval for Banner Maxx is 14 to 21 days. |
| Daconil Ultrex |
— |
1.4 lb |
| Daconil WeatherStik 6F |
— |
13/8 pt |
| Garden Fungicide |
2¼ t. |
— |
| myclobutanil |
| Immunox |
2 T. |
— |
| propiconazole |
| Banner Maxx |
— |
2 to 4 fl oz |
| Systemic Fungicide |
1 T. |
— |
| tebuconazole |
| Disease Control for Roses, Flowers, and Shrubs |
|
— |
Dogwood Canker
Dogwood canker, a serious disease of unknown cause, was first reported on stems and trunks of white flowering dogwood in Virginia in 1969. Since then, this disease has been seen in several southeastern states, including Tennessee, where considerable effort has been made in recent years to identify the causal agent. Dogwood canker has not been found in Alabama, but diseased trees have been found in several Tennessee counties bordering the state. This disease has been identified on trees in landscapes,
field nurseries, and forest settings.
Canker has been reported to occur as two distinct symptom types. Some trees show sunken bark areas that girdle the stems or trunks, eventually killing the upper canopy of the tree. Other trees display rough areas of bark with associated swellings in two or more locations along the trunk or main branches. Often these roughened, swollen cankers are invaded by insects.
Control of dogwood canker involves removal of cankered limbs or trees. When establishing dogwoods, homeowners should carefully select trees free of any swellings or cankers on the limbs and trunks.
Virus Diseases Of Dogwood
To date, six viruses have been found to infect dogwood, but only two, cherry leaf roll virus and arabis mosaic virus, cause definite symptoms on the foliage. Because of the few reports of dogwoods with virus-like symptoms, these diseases are considered unimportant.
Cherry leaf roll virus (CLRV) may cause a variety of symptoms on dogwood leaves, including ringspots,
mosaics, and oak-leaf patterns. Some twisting of bracts has been associated with CLRV infections of dogwood. Generally symptoms occur early in the spring and disappear as the weather warms. Research also has shown that this virus may cause significant stunting of dogwood.
Arabis mosaic virus (ArMV) causes yellowed leaf tips or a light green and white mosaic.
It is not known how these viruses are transmitted in nature, but both viruses have a wide host range. Dogwoods might serve as over-wintering hosts in some cases for these viruses.
Because virus infections of dogwood are rare, no preventive measures are really necessary. When
establishing dogwoods, inspect the foliage for unusual color patterns on the leaves. Removal of diseased
trees in home landscapes may slow further disease spread.
Dogwood Decline
A number of factors other than disease may contribute to the decline of dogwood in landscape settings.
With a shallow root system, dogwoods are highly sensitive to drought conditions—particularly
newly planted trees in full sun—and tree death is not uncommon. The effects of a water shortage on tree health are aggravated by the increased demand for water by the trees exposed to high temperatures. Poor site selection and improper tree establishment also greatly increase the sensitivity of dogwood to drought stress. Wounding of dogwood with mowers and other lawn tools (for example, weedeaters) also may kill the tree or favor invasion of trunk wounds by the dogwood borer. The kousa dogwood, a tree well adapted to temperate climates, has sometimes proven sensitive to low temperature winter injury following
a warm fall.
Poor foliage color, unthrifty plant growth, twig dieback, and possibly tree death are typical symptoms of
dogwood decline. An upward folding of the leaves at the mid-rib and downward at the tip are often seen on trees suffering from drought during the hot summer months. Later, a marginal leaf burn characterized by the browning of the tissues around the edge of the leaves may develop on severely stressed trees. Some defoliation may also be seen. The oldest leaves often are the first to show the effects of heat and drought stress. Death, particularly of recently transplanted dogwood, will occur unless the trees are properly watered.
Dieback and bark splitting are typical symptoms of cold injury on both the kousa and flowering dogwood.
Bark splitting is usually seen on the south or southwestern sides of the tree trunk.
Dogwood decline often can be prevented by following good tree establishment and maintenance practices.
Dogwoods are an understory tree in forest settings and are best adapted to well-drained, slightly acidic soils on partially to fully shaded sites in home landscapes. Well-caredfor trees will, however, prosper in full sun.
Newly established dogwoods are especially sensitive to extreme heat and drought conditions. Planting dogwood in the fall rather than in the spring allows the tree enough time to grow a good root system, thereby increasing its chances of surviving Alabama’s hot summers. Burlapped and container-grown trees are usually easier for homeowners to successfully establish than bare-root dogwoods.
Poor site preparation often accounts for the poor growth or death of dogwood. Add lime and fertilizers according to soil test recommendations and deeply work the soil. Amend sandy soils with one part peat moss, finely milled pine bark, well-rotted sawdust, or leaf compost to two parts of soil. The hole should be deeper and wider than the root ball to ensure good root development. Planting shallow-rooted trees and
shrubs like dogwood too deep is a common mistake made by many homeowners. Firming the soil while filling the hole should minimize settling of the root ball below the soil surface. After planting, the root ball should sit at or slightly above the soil level.
A 2- to 3-foot circle around the base of new and established dogwoods should be mulched with rotted sawdust, pine straw, or aged pine bark to hold moisture in the soil and prevent mechanical injury to the base of the trunk by mowers and other equipment. Occasional heavy watering is needed on new trees. Established trees should be watered about every 5 to 7 days during extended periods of hot, dry weather. Surface irrigate slowly to get water to all the roots.
Table 6. Chemical Control of Powdery Mildew
| Fungicide |
Rate |
Comments |
| Per gal |
Per 100 gal |
| azoxystrobin |
Foliar Spray:
Make first application when flower buds show color and repeat every 7 to 14 days until the bracts fall.
On badly diseased trees, continue fungicide applications until the new leaves mature in mid-June.
Refer to label for the recommended application interval for each fungicide. |
| Heritage 50W |
— |
1 to 4 oz |
| myclobutanil |
| Immunox |
2 T. |
— |
| Eagle 40W |
— . |
3 to 6 oz. |
| propiconazole |
| Banner Maxx |
— |
2 to 4 fl oz |
| Systemic Fungicide |
1 T. |
— |
| Tebuconazole |
| Disease Control for Roses, Flowers, and Shrubs |
1.5 T. |
— |
| thiophanate-methyl |
| 3336 50W |
2 ½ t. |
12 to 16 oz |
| 3336 4.5F |
1 T. |
10 to 20 fl oz |
| Halt 50W |
2 ½ t. |
— |
| thiophanate-methyl + mancozeb |
For more information, contact your county Extension office. Visit http://www.aces.edu/counties or look in your telephone directory under your county's name to find contact information.
Issued in furtherance of Cooperative Extension work in agriculture and
home economics, Acts of May 8 and June 30, 1914, and other related
acts, in cooperation with the U.S. Department of Agriculture. The Alabama
Cooperative Extension System (Alabama A&M University and Auburn
University) offers educational programs, materials, and equal
opportunity employment to all people without regard to race, color,
national origin, religion, sex, age, veteran status, or disability.
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