- Dogwood Anthracnose
- Host Plants:
- Symptoms & Disease Cycle:
- Dogwood Anthracnose (Discula) – Trees
- Key Points
- Additional Resources
- Connecticut State The Connecticut Agricultural Experiment Station
- Dogwood Diseases & Insect Pests
- Insects & Other Pests
- Other Problems
- How to Handle a ‘Diseased Dogwood’
- Identifying and Treating Harmful Dogwood Diseases
- Dogwood Anthracnose – Information About Dogwood Blight Control
- Dogwood Anthracnose Information
- Controlling Dogwood Blight
The fungus Discula destructiva causes dogwood anthracnose leaf blight and canker.
Dogwood anthracnose infects flowering (Cornus florida) and Pacific dogwoods (C. nuttallii). Kousa dogwood (C. kousa) is also susceptible to infection but is highly resistant to the disease and typically suffers only minor leaf spotting. Other common landscape dogwoods, such as Tatarian dogwood (C. alba) and redosier dogwood (C. sericea) are also resistant to the disease.
Symptoms & Disease Cycle:
Discula destructiva was introduced into eastern North America from Asia in the late 1970s and quickly spread throughout the region, decimating natural populations of flowering dogwood in southern New England. Because D. destructiva is non-native in North America, flowering dogwood has no natural defense against the pathogen, allowing the fungus to spread unchecked within the tree. Under ideal environmental conditions, dogwood anthracnose can be the sole cause of death. Foliar symptoms of infection range from angular-shaped leaf spots and blotches, marginal leaf scorch and a complete blight of infected foliage. Leaf spots are round to blotchy and have tan centers with reddish-purple margins. Additionally, succulent shoots and small stems can be killed and perennial cankers can develop on larger branches. Stem and branch cankers disrupt water and mineral transport, leading to a progressively worsening canopy dieback. Vascular cambium infected with dogwood anthracnose is chocolate brown in contrast to the pale tan color of healthy sapwood.
Another common symptom of infection on flowering dogwood is the prolific formation of epicormic sprouts adjacent to large branch cankers. This creates an abundance of small-diameters stems within shaded, interior portions of the canopy that are readily attacked by the fungus, increasing overall inoculum. The fungus requires abundant moisture, humidity and shade to cause disease. Thus, lower canopy branches are most susceptible to infection. Once established, the pathogen spreads upward within the canopy. Discula overwinters within diseased foliage and stem cankers, initiating new infections in the spring. Early in the growing season, fruiting structures erupt through the bark of infected twigs and on the underside of spotted leaves. During wet weather, copious numbers of spores are extruded and spread via splashing water and wind to nearby shoots, leaves and flowers.
There are a number of resistant species and varieties of dogwood available that greatly reduce the need for disease management. Principally, Kousa dogwoodis naturally resistant and provides many of the same landscape features that have made flowering dogwood so popular. Numerous C. kousa × C. florida hybrids and disease-resistant C. florida cultivars are also available. Dogwood anthracnose severity is inversely related to available sunlight. Therefore, trees should be planted only in full sun with no surrounding plantings. Prune and discard blighted shoots and stems as they develop and remove any epicormic sprouts that form as a result of the disease. Large, perennial cankers on scaffold branches are more difficult to manage, since removal may serious degrade the aesthetic value and overall health of the tree. Collect and discard all infected leaves that are shed throughout the growing season. Limit additional stresses, such as string trimmer and mower damage, that may attract secondary pests (e.g. dogwood borer) and pathogens (e.g. stem cankering pathogens like Phomopsis and Cytospora). During extended dry periods, provide trees with a soaking irrigation of the root zone and maintain a 2-3 inch layer of composted mulch over the root zone. During periods of wet spring weather, fungicide use may be warranted to protect green shoots and leaves on high-value flowering dogwoods. Begin fungicide applications when buds open and continue with additional treatments per label directions to maintain protection.
Dogwood Anthracnose (Discula) – Trees
The early symptoms of discula anthracnose begin in mid to late May as leaf spots with tan or purple borders
- In the past, anthracnose was the most serious disease of dogwoods in the landscape and our forests but it is now less common. It causes dieback or even death of infected trees.
- The early symptoms begin in mid to late May as leaf spots with tan or purple borders. In wet weather these spots can rapidly enlarge and kill the entire leaf. These blighted, drooping leaves can remain hanging on the branches in wet weather before defoliation occurs.
- The disease spreads from infected leaves into the twigs and branches and can cause dieback of the limbs. Young green stems and water sprouts are especially susceptible. Dark cankers will cause stem girdling and dieback. On older branches, the wood under the bark will appear dark brown in contrast to healthy light-colored wood. If the dieback reaches the main trunk the entire tree can be killed.
- To distinguish this disease from other leaf spots, examine the underside of the leaves (with a hand lens or magnifying glass) for numerous small tan to brown dots, about the size of a printed period, scattered within the blighted tissue. These dots are the source of spores that will be washed away by rain or dew, or spread by insects to healthy leaves and neighboring trees. The disease overwinters in twig and stem cankers that initiate new infections in the spring.
Under severe disease conditions, the flower bracts can become spotted.
- 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.
- Diagnosing Problems of Flowering Dogwood
- Flowering Dogwood Trees: Selection, Care, and Management of Disease Problems
- Dogwood Insect Pests: Identification and Management
Connecticut State The Connecticut Agricultural Experiment Station
Dogwood anthracnose is considered the most serious disease of flowering dogwood (Cornus florida) in Connecticut and the Eastern Seaboard. It is also an important disease of Pacific Dogwood (Cornus nuttallii) in the West. The causal agent is the fungus Discula destructiva, and as the name suggests, this pathogen is highly destructive. It is believed that the fungus was probably simultaneously introduced into the East and West Coasts of the United States in the mid-1970s. Since its introduction, dogwood anthracnose has resulted in the death of many dogwoods in forests, woodlots, and landscapes.
SYMPTOMS AND DISEASE DEVELOPMENT:
Initial foliar symptoms develop in May and June as brown spots up to ¼ inch in diameter that are visible on both the upper and lower leaf surfaces (Figure 1). These spots can be circular or irregular in shape and frequently develop distinctive smoky, purple-brown margins (Figure 2).
Figure 1. Necrotic spots on leaves. Figure 2. Smoky, purple-brown rings on foliar lesions.
The flower bracts are also susceptible to infection and develop reddish or brownish spots or blotches. These are most prevalent when wet conditions occur during flowering.
Under certain conditions, pinpoint, brownish-black fruiting structures can be seen in the centers of the foliar spots or lesions. Spots on the leaves usually become so numerous that they coalesce, which results in the development of large, dead areas on the leaves. When entire leaves become necrotic, they usually droop and rather than falling off, they remain on the tree throughout the fall and into the winter. The persistence of infected leaves on the tree during winter is a distinctive characteristic and can help in diagnosis. The presence of infected leaves on the tree also serves as an important source of overwintering inoculum, since fungal spores capable of initiating new infections in spring are produced on these leaves.
When the whole leaf becomes infected, the fungus grows into the petiole and then into the twig where it causes cankers. Cankers are often tan, slightly sunken, elliptical areas of bark and are readily distinguished from surrounding healthy bark. The fungus can also directly infect shoots
Figure 3. Progressive dieback of branches up the tree.
during spring and fall. These infections develop into very small cankers. If left unchecked, these cankers increase in size and eventually girdle the affected tissues (e.g., twigs, stems, branches, or the main trunk). Symptoms and branch dieback typically begin on the lower limbs and move progressively up the tree (Figure 3). This pattern of dieback appears to be associated with poor air circulation in the lower canopy, which results in tissues staying wet for longer periods of time. This makes them more susceptible to infection. Some trees attempt to compensate for the loss of limbs by sending out sprouts from the trunk (epicormic sprouts) but these sprouts are highly susceptible to infection. Sprout infections usually spread quickly to the trunk and cause severe cankers and splits in the bark. These cankers readily develop into tree-killing cankers.
Dogwood anthracnose is more aggressive on trees that have been predisposed or weakened by environmental and cultural factors. Among some of the more common predisposing factors are drought stress, poor site selection (e.g., full sun, windy or open area, or thin or rocky soil), mechanical injury (e.g., damage from string trimmers and lawn mowers), and soil compaction.
DISEASE MANAGEMENT STRATEGIES:
The effects of dogwood anthracnose can be minimized by following an integrated approach toward managing the disease.
Rake and remove fallen leaves to remove important sources of overwintering inoculum.
Prune and remove cankered limbs and dead wood. This helps to reduce the ability of the fungus to grow into the main trunk where girdling, tree-killing cankers can develop.
Maintain tree vigor by following sound cultural practices. It is especially important to avoid drought stress so watering the tree during periods of low rainfall is essential. Mulching is also helpful since it helps maintain soil moisture, moderate soil temperatures, and minimize chances for mechanical injuries.
Provide adequate spacing for good air circulation. Since the fungus requires free water on plant surfaces in order to infect, any practices that reduce periods of wetness can help to minimize chances for infection.
Control insects and avoid unnecessary mechanical injuries.
Plant resistant species or cultivars. Although Cornus kousa (Kousa Dogwood) is less susceptible to infection than C. florida (Flowering Dogwood), it can become infected in years when there is heavy infection pressure and favorable weather for disease development. Breeding programs that have made crosses between C. florida and C. kousa have yielded promising cultivars such as the ‘Stellar’ Hybrid series, ‘Aurora,’ ‘Celestial,’ ‘Constellation,’ ‘Ruth Ellen,’ ‘Stardust,’ and ‘Stellar Pink.’
Fungicides are another component of disease management. Applications can be made at budbreak, when the bracts fall, and 4 weeks later. A late-summer fungicide application when fruit and leaves begin to color has also been found to be helpful. Among the compounds registered for homeowner use in Connecticut are chlorothalonil, copper hydroxide, mancozeb, and thiophanate-methyl. Consult the label for dosage rates and safety precautions.
Dogwood Diseases & Insect Pests
The flowering dogwood (Cornus florida) is a small, deciduous ornamental tree that is native throughout the eastern United States. Although dogwoods are well adapted to South Carolina, they can be affected by many pests and diseases. Maintaining healthy dogwood trees by following the recommended cultural practices is the first line of defense in reducing any of these problems. More information about growing dogwoods is available in HGIC 1010, Dogwood.
Powdery Mildew: Erysiphe pulchra (formerly Microsphaera pulchra) is the fungus that attacks leaf surfaces and tender shoots and causes powdery mildew. New growth is covered with a fine, white, powdery coating, typically on the upper surfaces of the leaves. Infected leaves exhibit marginal leaf scorch, dead patches, reddish discoloration, yellowing and premature defoliation. Spores are spread by wind to surrounding dogwood plants.
Powdery mildew on dogwood (Cornus florida) leaves.
James Blake, ©2007 HGIC, Clemson Extension
Powdery mildew is most common in dense, shady areas where the air circulation is poor. Warm, dry days and cool, damp nights favor disease development.
Prevention & Treatment: Most powdery mildews of landscape trees occur late in the summer and are therefore of little consequence. Infection that begins early in the season can be devastating, and the use of fungicides may be warranted.
Cultural controls should be the first line of defense. Begin by raking up and destroying all fallen leaves. Prune out dead and infected branches and twigs. Improve air circulation and sunlight penetration around the tree by removing overhanging branches and crowding vegetation. Resistant species and cultivars are available and should be considered for new plantings. Cultivars of the oriental dogwood Cornus kousa (such as ‘Milky Way’, ‘Milky Way Select’, and ‘National’) and many of the Cornus florida x Cornus kousa hybrids (such as ‘Aurora’, ‘Constellation’, ‘Celestial’, and ‘Stellar Pink’) are generally resistant to powdery mildew. The flowering dogwood (Cornus florida) cultivars ‘Appalachian Joy’, ‘Appalachian Blush ‘, ‘Appalachian Snow’, and ‘Appalachian Mist’ are very resistant to powdery mildew. ‘Cherokee Brave’, ‘Springtime’, and ‘Pygmy’ have partial resistance. All other flowering dogwoods (C. florida) are susceptible. Red-twig dogwood (C. sericea) is very susceptible to powdery mildew.
If disease is severe enough to warrant the use of fungicides, be sure that the dogwood is a valuable specimen and the spray equipment can provide good coverage. For fungicides to be effective, they must be applied as soon as symptoms are noticed. Very effective fungicides for dogwood powdery mildew control include myclobutanil and propiconazole. Some control can also be obtained with triadimefon, thiophanate methyl, sulfur, or copper fungicides (see Table 1 for specific products). Product labels will provide information on how often to spray. The first four fungicides listed have systemic properties and can be sprayed less often than sulfur or copper fungicides. When powdery mildew persists and sprays are repeated, it is recommended to alternate fungicides to decrease the chance of fungi developing resistance.
Spot Anthracnose: This disease is caused by the fungus Elsinoe corni, one of the most common leaf diseases of flowering dogwoods. The flower bracts are usually attacked first and then the leaves, young shoots, and fruit of dogwoods, primarily during wet spring weather. Symptoms are small (⅛ inch), tan spots with reddish-purple borders. When infection is severe, these spots can cause flower bracts and leaves to become wrinkled and distorted. As further infections occur, individual spots eventually merge to form larger spots. The centers may drop out. This fungus survives from year to year on infected twigs, fruits, and other tissues.
Spot anthracnose on dogwood (Cornus florida) petals.
Joey Williamson, ©2009 HGIC, Clemson Extension
Frequent rains or extended periods of high humidity are needed for disease development. When dry weather follows bud swell and bloom, the symptoms are rarely seen on the flower bracts. If spotting does not appear on the bracts, the disease may not be severe on the leaves.
Prevention & Treatment: In most cases, this disease doesn’t result in significant damage, but severe and repeat infections each year can significantly weaken a tree. Thin the canopy to increase air movement. Planting species and cultivars with some degree of disease resistance is an excellent option for managing this problem in the landscape.
The disease-tolerant and resistant varieties include:
- Kousa dogwood (Cornus kousa) ‘National’, ‘Milky Way Select’
- Flowering dogwood (C. florida) ‘Cherokee Brave’, ‘Cherokee Chief’, ‘Welch’s Bay Beauty’, ‘Cherokee Princess’ and ‘Springtime’
- Rutger’s Hybrid – ‘Stellar Pink’
The worst spot anthracnose has been reported on Cornus florida ‘Rainbow’ and ‘Cherokee Daybreak ‘.
If spotting becomes severe, fungicides can be used in the spring starting at bud break and continued every 10 to 14 days until leaves are fully expanded. Fungicides available for use include chlorothalonil, mancozeb, propiconazole, thiophanate-methyl, or copper fungicides (see Table 1 for specific products). Fungicides for spot anthracnose will also control dogwood anthracnose (canker anthracnose). Apply all chemicals according to directions on the label.
Dogwood Anthracnose (Discula Anthracnose): This is a relatively new disease of dogwood in South Carolina, and it is caused by the fungus Discula destructiva. Dogwood anthracnose is most severe only in areas of the state that are higher than 2000 feet. A few cases have been reported at lower elevations where dogwoods are grown in very cool, moist, shady locations. It is a serious disease capable of killing large numbers of trees and most Cornus species can become infected.
The first symptoms that appear in the spring are spots on the leaves and flower bracts. Leaf symptoms develop first in the lower canopy and progress up the tree. Infected leaves have tan spots with purple edges, dry brown margins or large blotches on them. Blighted gray or drooping leaves hang on the twigs and are often the first symptoms noticed during cool, wet weather.
Symptoms of Discula anthracnose on dogwood (Cornus florida) leaves.
Joseph O’Brien, USDA Forest Service, www.ipmimages.org
Canker on dogwood (Cornus florida) caused by Discula anthracnose (bark removed).
Joseph O’Brien, USDA Forest Service, www.ipmimages.org
Infection spreads into the shoots, main branches, and trunk causing brown sunken areas (cankers) to occur. Cankers can girdle and kill individual branches or twigs. Multiple cankers can girdle the main trunk and eventually kill the tree. Diseased trees produce numerous epicormic shoots or “water sprouts” on the lower trunk and lower limbs, which soon become infected.
Prevention & Treatment: Planting resistant species and cultivars is an excellent option for managing this disease in the landscape. Kousa dogwood (Cornus kousa) is generally resistant to dogwood anthracnose and is a better choice for replanting in sites where dogwoods have died from this disease. Crosses between Cornus kousa and Cornus florida (Rutger’s Hybrids) have greater disease resistance to dogwood anthracnose and include: ‘Aurora’, ‘Celestial’, ‘Galaxy’, ‘Ruth Ellen’, ‘Star Dust’, ‘Stellar Pink’, and ‘Constellation’. Cornus florida ꞌAppalachian Spring’ has a high level of resistance to anthracnose.
A combination of cultural and chemical measures is necessary to control this disease. Effective control may be possible if the disease is detected before branch dieback begins.
During hot, dry summer weather, prune and dispose of all dead or cankered twigs and limbs. Remove all “water sprouts.” Rake and remove fallen leaves. Do not leave dead leaves attached to the tree. Improve air circulation and light penetration by removing understory plants and crowding vegetation.
Avoid high applications of nitrogen fertilizer, since this can promote very succulent (susceptible) new shoots. Maintain healthy dogwoods by following recommended cultural practices.
Avoid transplanting dogwood seedlings from the woods as these plants may harbor the fungus.
Fungicide sprays to protect the new leaves and shoots need to begin at bud break in early spring. Fungicides for spot anthracnose will also help to control dogwood anthracnose. These include: chlorothalonil, mancozeb, propiconazole, thiophanate-methyl, or copper fungicides (see Table 1 for specific products). Maintain a protective covering of fungicide when new growth is present. Apply all chemicals according to directions on the label.
Septoria leaf spots on dogwood (Cornus florida).
Division of Plant Industry Archive, Florida Department of Agriculture and Consumer Services, www.ipmimages.org
Cercospora & Septoria Leaf Spots: These leaf spot diseases are caused by the fungi Cercospora cornicola and Septoria species, respectively. They most commonly occur during the wet summer months, and may become so numerous that they cover the leaves by the end of summer. Heavily spotted leaves may be shed early. The light spotting seen on leaves of dogwood usually has little impact on tree health, but repeated years of early leaf drop can weaken the tree.
Cercospora and Septoria leaf spots are very similar in size and appearance. Both are small (⅛ to ¼ inch), angular to irregularly shaped and usually bordered by leaf veins. Spots caused by Cercospora species have tan-brown areas with diffuse borders. Septoria leaf spots are a dark brown purple in color, later developing light brown or gray centers with dark borders.
Prevention & Treatment: Clean up and dispose of infected leaves on the ground and on the tree, if possible, since this is where these fungi survive the winter. For severe infections, fungicides containing chlorothalonil, thiophanate-methyl, or mancozeb can be sprayed (see Table 1 for specific products).
Insects & Other Pests
Although insects often damage dogwood trees, the damage is usually minor. If the tree is planted in full sun with limited water or under other stress, the damage can be serious. Most insect damage occurs on the trunk and branches of dogwoods. Commonly occurring insect pests of dogwood include the dogwood borer, dogwood club-gall midge, and scales.
Dogwood borer adult.
James Solomon, USDA Forest Service, www.ipmimages.org
Dogwood Borer: The dogwood borer (Synanthedon scitula) is the larva (immature form) of a clearwing moth that resembles a wasp. The borer is off-white in color with a reddish-brown head. It is about 5/8-inch long at maturity. The female moth lays eggs on the bark.
The borers can become established only if they locate a wound or opening in the bark. Inside the tree, they feed on the cambium, which is where water and food-carrying structures of the tree are produced. If the cambium is destroyed, branches or the entire tree will die. Leaves of dogwoods infested with the dogwood borer will often turn red and drop early. Bark sloughs off around holes on the trunk or branches. In late summer, a brown sawdust-like borer frass (insect waste) may be seen near or below the holes. Infested young trees can be killed in one to two seasons. Large, established trees that are infested often lack vigor and have rough, knotty areas on the trunk and large branches.
Prevention & Control: The best prevention is to keep trees healthy by fertilizing, watering, and mulching. In addition, protect the trees from unnecessary wounding, such as from lawn mowers and string trimmers, as this will reduce the chances of infestation. Permethrin is labeled for use by the homeowner against dogwood borer (see Table 1 for specific products). Since dogwood borer adults may be present from late April through July, several applications may be needed for good control. Begin treatment in early May and repeat four times at three-week intervals. Thoroughly spray the trunk, major branches and any wounds on the bark. Read and follow all label instructions and precautions.
Damage on dogwood (Cornus florida) caused by dogwood club-gall midge.
Joey Williamson, ©2013 HGIC, Clemson Extension
Dogwood Club-Gall Midge: The dogwood club-gall midge (Resseliella clavula) is a small fly, about 1/16-inch long. The female lays eggs in tiny terminal leaves of the dogwood. The larva hatches and enters the shoot. In response to the feeding and growth of the larva, a ½-1 inch long club- or spindle-shaped tubular swelling (gall) forms at the tip or along the stem. The twig beyond the gall may die. In early fall, the larvae make exit holes in the galls. They drop to the ground where they survive the winter. An early symptom of a club-gall midge presence is a wilted, deformed leaf. A light infestation is not serious. A heavy infestation can stunt a tree.
Control: Twigs with galls should be cut off and burned before larvae make their exit holes.
Scales: Several scale insects are pests of dogwood. Scales are unusual insects in appearance. They are small and immobile, with no visible legs. Scales vary in appearance depending on age, sex, and species. They may be found on leaves or stems and look like small brownish, grayish or blackish bumps. They feed on sap by piercing the leaf or stem with their mouthparts and sucking. If infestations are very heavy, they may cause leaf yellowing, stunting, or branch dieback. Adult scales are relatively protected from insecticides by their waxy covering. However, immature forms, called crawlers, are susceptible.
Control: For heavy infestations, spray with horticultural oil in the spring to kill many adults and eggs by smothering them. Oil should be applied before new growth begins and again after flowering. Be sure to thoroughly coat all of the branches. Avoid using insecticides unless the plant is very valuable and in serious danger from scale. The use of the horticultural oil is a safer alternative to insecticides for spraying upward into a large tree (see Table 1 for specific products).
Insecticides will often kill the naturally occurring enemies of scale. If insecticides are going to be used, spray when crawlers are observed. Monitor the crawler emergence with sticky cards, double-faced tape wrapped around a branch, or by putting an infested shoot or leaf into a baggie and watching for crawler movement. Crawler activity often coincides with the flush of new plant growth in the spring. However, some scale species may have overlapping generations with an extended crawler emergence period, such as along the coast. Insecticides labeled for use by homeowners against scale crawlers on dogwood include bifenthrin, cyfluthrin, permethrin, lambda cyhalothrin, and malathion (see Table 1 for specific products). Repeat treatments in 10 days. Read and follow all label instructions and precautions.
Poor leaf color, unhealthy plant growth, twig dieback, and even tree death are typical symptoms of distressed dogwoods. A number of factors other than insects or diseases can contribute to the decline of dogwoods in the landscape, especially mower injury, over-fertilization, and poor growing conditions.
Leaf scorch caused by drought stress on dogwood (Cornus florida).
Joey Williamson, ©2014 HGIC, Clemson Extension
Leaf Scorch: Leaf scorch is caused by environmental conditions that are too dry. Leaves have dry and browning edges. On severely stressed trees, drying and browning of the areas between the veins and leaf drop can occur.
This condition looks just like a disease, but it isn’t. Dogwoods have a very shallow root system, and thus are very susceptible to drought stress, especially newly planted trees in full sun.
Prevention & Treatment: Watering during dry spells is the key to avoiding leaf scorch. After transplanting, be sure to water as needed during the first summer and fall to avoid leaf scorch. Apply a thick layer of mulch (3 to 4 inches) that extends out beyond the foliage of the tree. Do not grow grass over the root system area.
Caution: Pollinating insects, such as honey bees and bumblebees, can be adversely affected by the use of pesticides. Avoid the use of spray pesticides (both insecticides and fungicides), as well as soil-applied, systemic insecticides unless absolutely necessary. If spraying is required, always spray late in the evening to reduce the direct impact on pollinating insects. Always try less toxic alternative sprays first for the control of insect pests and diseases. For example, sprays with insecticidal soap, horticultural oil, neem oil extract, spinosad, Bacillus thuringiensis (B.t.), or botanical oils can help control many small insect pests and mites that affect garden and landscape plants. Neem oil extract or botanical oil sprays may also reduce plant damage by repelling many insect pests. Practice cultural techniques to prevent or reduce the incidence of plant diseases, including pre-plant soil improvement, proper plant spacing, crop rotation, applying mulch, applying lime and fertilizer based on soil test results, and avoiding over-head irrigation and frequent watering of established plants. Additionally, there are less toxic spray fungicides that contain sulfur or copper soap, and biological control sprays for plant diseases that contain Bacillus subtilis. However, it is very important to always read and follow the label directions on each product. For more information, contact the Clemson Extension Home & Garden Information Center.
Table 1. Insecticides & Fungicides to Control Dogwood Insect Pests & Diseases.
|Insecticides & Fungicides||Examples of Brand Names & Products|
|Bifenthrin||Ferti-lome Broad Spectrum Insecticide Concentrate
Hi-Yield Bug Blaster Bifenthrin 2.4 Concentrate
Monterey Turf & Ornamental Insect Spray
|Chlorothalonil||Bonide Fungonil Multi-Purpose Fungicide
Hi-Yield Vegetable, Flower, Fruit & Ornamental Fungicide
Southern Ag Liquid Ornamental & Vegetable Fungicide
Garden Tech Daconil Fungicide Concentrate
Ortho Max Garden Disease Control
Tiger Brand Daconil
Ferti-lome Broad Spectrum Landscape & Garden Fungicide Conc.
|Copper-based Fungicides||Bonide Liquid Copper Concentrate
Camelot O Fungicide/ Bactericide Concentrate
Natural Guard Copper Soap Liquid Fungicide Concentrate
Southern Ag Liquid Copper Fungicide
Monterey Liqui-Cop Fungicide Concentrate
|Cyfluthrin||Bayer BioAdvanced Vegetable & Garden Insect Spray Concentrate|
|Horticultural Oil||Bonide All Seasons Spray Oil Concentrate
Ferti-lome Horticultural Oil Spray Concentrate
Southern Ag Parafine Horticultural Oil
Monterey Horticultural Oil Concentrate
Summit Year Round Spray Oil Concentrate
|Lambda Cyhalothrin||Spectracide Triazicide Insect Killer for Lawns & Landscapes Concentrate
Martin’s Cyonara Lawn & Garden Concentrate
|Malathion||Bonide Malathion 50% Insect Control Concentrate
Ortho Max Malathion Plus Insect Spray Concentrate
Southern Ag Malathion 50% EC
Spectracide Malathion Insect Spray Concentrate
Hi-Yield 55% Malathion Spray
Martin’s Malathion 57% Concentrate
Tiger Brand 50% Malathion
Gordon’s Malathion 50% Spray
|Mancozeb||Bonide Mancozeb Flowable
Southern Ag Dithane M-45
|Myclobutanil||Spectracide Immunox Multi-Purpose Fungicide Concentrate
Ferti-lome F-Stop Lawn & Garden Fungicide
|Permethrin||Bonide Eight Insect Control Vegetable Fruit & Flower Concentrate
Bonide Total Pest Control – Outdoor Concentrate
Hi-Yield Indoor/ Outdoor Broad Use Insecticide
Tiger Brand Super 10 Concentrate
Martin’s Vegetable Plus Concentrate
|Propiconazole||Bonide Infuse Systemic Disease Control Fungicide
Ferti-lome Liquid Systemic Fungicide
Banner Maxx Fungicide
Martin’s Honor Guard PPZ
|Thiophanate-methyl||Southern Ag Thiomyl Systemic Fungicide
Cleary’s 3336-WP Turf & Ornamental Fungicide
How to Handle a ‘Diseased Dogwood’
Q. I have a dogwood tree in my yard I’m really concerned about. It was planted about three years ago in what I now realize is a very hot afternoon sun location (probably not ideal). Its leaves look brown every year and it has not yet flowered. I thought it was drought stressed, so this season I really kept on top of watering it with a soaker hose. It started leafing out, but by early summer the leaves began to look dry and about 50% of each leaf curled inward. An arborist I called said the tree suffers from anthracnose and will need an annual fungicide spray; non-organic. I am hoping there are other options.
- —Jennifer in South Jersey
A. You don’t specify if you have one of the native varieties or the Asian import known as the Kousa dogwood, but you’ve already shown yourself to be a better arborist than your arborist by diagnosing the problem as probably being caused by a bad location and not a disease.
Yes, dogwood trees are prone to anthracnose, a fungus that affects many plants, especially in damp, wet seasons. But last summer’s hot and dry weather kept anthracnose problems to a minimum. And your symptoms don’t match. If your tree were attacked by anthracnose, you would have complained about spots and blotches on the leaves, not late arrival (which is normal for dogwoods) or leaf curl—which can be caused by a number of problems but simple-minded me tends to think they curled up because they were roasting in the sun.
Dogwoods are one of those great conundrums of the plant world—they need sun to bloom well, but they also sunburn easily. And they despise drought. And all trees do poorly if they aren’t watered well during their first few years of life. So if you got your tree off to a bad start by failing to water it carefully the year it was planted, it could easily have been weak and behind schedule when that historically hot summer blew through.
Try and figure out which type you have. The native variety (scientific name Cornus florida) is so acclaimed for its fabulous blooms that its common name is ‘Flowering Dogwood’ (even though all dogwoods produce pretty posies), but it blooms the earliest of any dogwood—in April or May, before the leaves appear. So if you’re cleverly pruning it in the summer, fall or winter, you’re cutting off all the buds and that’s the reason for your lack of flowers. The only safe time to prune dogwoods and other Spring blooming plants is right after they flower.
Because the native does bloom so early, its flowers can also be lost to a late hard frost. And you have to be patient; it takes dogwoods a while to settle in before they bloom, and it wouldn’t be unusual to still be waiting for blooms on a three year old.
But no matter which type it is, it doesn’t want to sit out being fried in the summertime. No spray in the world is going to help a plant that’s trapped in a desperately wrong place. Because it’s only three years old, I’m going to suggest we stress it one more time with a move; no fun for the plant, but it will end its yearly heat stress. Replant it in a location that gets full morning sun and some shade late in the day. Not the opposite! Disease prone plants need to dry off first thing in the morning, and dogwoods do tend to get the horticultural sniffles when conditions are poor. (So trading full sun for morning shade would be just as bad as what you have now, but in reverse.)
I suggest you move it now if your ground isn’t frozen yet. The tree should be dormant and there aren’t the distractions of Spring. Follow the directions in our previous Question of the Week on moving plants. When you get the tree to its new location, dig a nice wide hole, but keep it shallow. Dogwoods especially need to planted high in the ground or they’ll develop energy-sucking cankers around the portions of the bark that are underground You must see the root flare above ground or the tree will not prosper. As we recommend with all newly planted trees, refill the hole only with the removed soil; don’t add any soil amendments underground.
Dogwoods thrive in naturally rich acidic soil, so after planting, spread an inch of milled peat moss around the base of the tree, and then cover it with an inch of high-quality yard-waste compost. Don’t use wood, bark or root mulch; those things breed anthracnose like mad! And don’t touch the trunk with any mulch; leave a good six inches of open area all around. But do take the peat moss and compost mulch out as far as the tips of the furthest branches. Water well when you’re done and then provide supplemental water any week we don’t get an inch of rain. Be especially vigilant during hot, dry times.
The tree should thrive once it gets into the right location. To keep it healthy, keep the trunk clear of mulch and debris, don’t feed it chemical fertilizers and don’t use herbicides anywhere near it. But do freshen up the peat moss and compost mulch every Spring—and be sure the compost always goes on top. Compost on the surface of the soil is your best defense against diseases like anthracnose in years when the weather is wet.
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Identifying and Treating Harmful Dogwood Diseases
The dogwood tree is commonly grown for ornamental purposes, often as a standalone tree. It is popular for its exotic, bright-colored flowers. Some dogwood varieties grow red berries during the early winter season. Dogwoods are low-maintenance trees but they are susceptible to some garden diseases. Early detection and disease management can help you to save your dogwoods from many deadly infections.
The anthracnose disease affects flowering varieties of dogwoods like the Pacific dogwood. Anthracnose disease spreads very quickly and it is critical to identify it during its nascent stage. It is caused by the Discula fungus. This disease propagates quickly in cool, slightly wet conditions that are associated with the late spring and fall season. Dogwoods exposed to extreme weather variations like extended dry spells or freezing winters become more vulnerable to anthracnose disease.
The symptoms first develop in the dogwood tree’s leaves. Initial indications include tan spotting along the upper portion of the leaves. Some spots may have a purple-colored rim to them. Some leaves could develop necrosis with a weathered look to the outer edges. A blight-like pattern develops on the stem during the late spring or the early fall season. The blight spots have a girdle-like shape. The spots are commonly found among the leaf nodes. Such blighted twigs develop a typical, bent appearance.
Mulching dogwoods is vital, particularly during the winters. Dogwoods exposed to alternative freezing and thawing patterns are more prone to fungal infections. You should apply a 3-inch thick mulch around your dogwood before the winter season sets in. You shouldn’t water the mulch repeatedly, i.e. keep it moistened but not wet and replace it every 3 weeks. Avoid irrigating the dogwoods with overhead irrigation. This system of spraying water creates extremely moist conditions in the upper part of the tree’s foliage. Such conditions are a thriving ground for fungal infections. You can also use organic fungicides. Spray the fungicide at regular intervals, with a minimum gap of 12 days.
Dogwood Canker Diseases
Cankers are essentially dead spots on a tree wherein the plant’s nutrition supply has been stopped. Dogwood cankers are commonly found on the main trunk area. A particular kind of canker disease called the Diffuse Canker is typical to dogwoods. It is caused by the canker fungus that spreads inside the bark, sucking-away the bark’s nutrition. The most serious but rare, Trunk Canker among dogwoods is caused by the Phytophthora fungus.
Most cankers are first found among the lower, slightly older branches. Once canker infection seeps into the bark, small callus-like formation is found on the main bark.
Short dry spells can stimulate canker infection. You should maintain proper soil moisture, particularly among young dogwoods. Hindered root development, often caused due to nearby structures can cause root suffocation. This too makes the tree susceptible to fungal infections. Older branches are more prone to canker infections. Ensure that you regularly prune-off dying and bent branches. Branches that are intensely twined around the main bark should be immediately pruned.
Leaf Spot Disease
Leaf spotting is common among dogwoods. If it isn’t detected early, spotting can spread to the dogwood fruit. It can cause widespread infection among the berries. This form of berry-spreading leaf spotting is caused by the Septoria fungus. Sometimes, it is difficult to determine the cause of leaf spots among dogwoods. It is often caused by other factors like soil nutrition deficiency. However, the fungal or Septoria spotting is more common in humid conditions.
Leaf Spot Identification
The symptoms include characteristic purple-colored spots on the leaves. The spots are often oval shaped. The spots may develop a grayish hue in their center during wet conditions. The purple border among leaf spots is the identifying mark of spotting caused by fungal infections. The duller, dark brown-colored spots could be caused by soil nutrition deficiency.
Leaf Spot Treatment
Nutrition-based spotting can be treated by enriching the soil bed with basic, NPK fertilizers and regular watering. However, fungal spotting needs systematic care. You should regularly prune the dogwood trees, using lightweight shears. This helps to minimize injury to the plant that is common during pruning sessions. Fungal leaf spot infections are known to spread quickly through injured sites on the tree. Spotting often initiates in damp soil conditions. Ensure that the soil bed is not waterlogged. You should use organic mulch made from pine bark to increase the water-draining capacity of the soil.
Dogwood Anthracnose – Information About Dogwood Blight Control
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 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 – this is how many infections started.