Dogwood trees, known for their blossoming in the spring and vibrant autumn leaves, are a beloved species of flowering tree. However, they are susceptible to various illnesses and pests.
Understanding these potential threats is the first step toward protecting your dogwood and ensuring its health and longevity.
In this guide, we’ll explore 17 common dogwood diseases and pests, their causes, symptoms, and, most importantly, how to prevent and treat them.
Managing diseases and pests is just one of the many things to learn about dogwood trees. I cover all the basics and more in my comprehensive Dogwood Tree Guide. It’s a must-read!
Dogwood Diseases
There’s a good chance your dogwood will never suffer from any debilitating disease, but if you do notice something wrong with your tree, it’s good to be familiar with the possible explanations.
1. Dogwood Anthracnose
Dogwood anthracnose is a serious fungal disease that affects dogwood trees. It’s caused by the fungus Discula destructiva, which can thrive and spread under wet, cool conditions.
Symptoms
Symptoms of dogwood anthracnose can vary depending on the severity of the infection. Early signs include small, purple-bordered leaf spots and blotches, which can be tan, brown, or purple in color.
As the disease progresses, these spots can expand, leading to large areas of dead tissue on the leaves. The disease can also cause cankers or sunken areas on the branches and trunk of the tree.
In severe cases, dogwood anthracnose can lead to extensive defoliation and death of the tree.
Prevention
Planting resistant varieties of dogwood can help reduce the risk of infection. Good air circulation around the tree can help reduce humidity levels, making conditions less favorable for the fungus.
Avoiding overhead watering can prevent the spread of the fungus as the disease can easily spread through water splashes.
Treatment
Treatment involves pruning and disposing of infected branches to prevent the spread of the disease. It’s important to sterilize pruning tools before and after use and between cuts to avoid spreading the fungus.
Fungicides containing chlorothalonil, mancozeb, or propiconazole are often recommended for treating dogwood anthracnose.
2. Spot Anthracnose
Spot anthracnose, also known as Elsinoë leaf spot, is a common disease in dogwood trees. It’s caused by the fungus Elsinoë corni.
Symptoms
Spot anthracnose is typically less severe than dogwood anthracnose. Symptoms include small, purple-bordered spots on the leaves, bracts, and sometimes the young shoots of the tree.
These spots are usually less than 1/8 inch in diameter and may have a tan or white center.
Prevention
Preventive measures for spot anthracnose are similar to those for dogwood anthracnose.
Regular cleaning of fallen leaves and debris around the tree can help remove potential sources of infection.
Ensuring good air circulation around the tree can also help reduce humidity levels, making conditions less favorable for the fungus.
Treatment
Treatment for spot anthracnose involves applying a suitable fungicide in the early spring when buds start to break. Fungicides containing chlorothalonil or mancozeb can be effective against this disease.
3. Powdery Mildew
Powdery mildew is a common fungal disease that affects many types of plants, including dogwood trees. It’s caused by the fungus Erysiphe pulchra.
Symptoms
Powdery mildew is easily recognizable by the white, powdery substance that appears on the leaves of the tree. The disease can cause the leaves to curl and may result in premature leaf drop.
In severe cases, powdery mildew can stunt the growth of the tree and reduce its vigor.
Prevention
Preventing powdery mildew involves planting resistant varieties of dogwood, ensuring good air circulation around the tree, and avoiding overhead watering which can create a humid environment that favors the fungus.
Regular cleaning of fallen leaves and debris around the tree can help remove potential sources of infection.
In addition, applying a bioassimilable sulfur-based compound can enhance the plant’s immune system and provide effective control against powdery mildew.
Treatment
Fungicides containing chlorothalonil, mancozeb, or propiconazole are often recommended for treating powdery mildew.
In addition, a study found that the combination of oil adjuvants and pyraclostrobin was highly effective in managing powdery mildew in plants.
4. Leaf Spot Diseases
Leaf spot diseases in dogwood trees can be caused by several different fungi, including Septoria, Cercospora, and Phyllosticta.
Symptoms
Symptoms of leaf spot diseases include small, round, or irregularly shaped spots on the leaves.
The spots may be tan, brown, or black, and they often have a purple or dark brown border. In severe cases, these diseases can cause premature leaf drop.
Prevention
Preventing leaf spot diseases involves removing fallen leaves and debris around the tree to remove potential sources of infection.
Ensuring good air circulation around the tree can also help reduce humidity levels, making conditions less favorable for the fungi.
In addition, a study found that a high nitrogen fertilization rate can impact the occurrence and severity of leaf spot diseases, so avoid applying excessive nitrogen.
Treatment
Treatment for leaf spot diseases involves applying a suitable fungicide such as chlorothalonil, mancozeb, or propiconazole.
5. Bacterial Leaf Scorch
Bacterial leaf scorch, caused by the bacterium Xylella fastidiosa, is a disease that can affect Dogwood trees.
This bacterium is xylem-limited, meaning it resides in the water-conducting tissues of the tree and can cause a disruption in the tree’s water transport.
Symptoms
Symptoms of bacterial leaf scorch include leaf scorching, where the leaf edges may turn brown, a phenomenon often confused with drought stress or nutrient deficiency.
The disease can cause a slow decline of the tree over several years.
Prevention
Preventing bacterial leaf scorch involves ensuring good water management for the tree. Water stress has been shown to enhance leaf scorch symptom severity and progression.
Therefore, maintaining proper irrigation and avoiding water stress can help in managing this disease.
Treatment
Effective treatment for bacterial leaf scorch in trees involves the use of antibiotics.
A study showed that American elms with bacterial-associated leaf scorch treated with oxytetracycline displayed a delay in symptom onset or remission of symptoms.
6. Fire Blight
Fire blight is a bacterial disease caused by Erwinia amylovora. While it’s more common in members of the Rosaceae family, it can also affect dogwood trees.
Symptoms
Symptoms of fire blight include wilting, blackening, and a “burned” appearance of branches. The disease can cause a slow decline of the tree over several years.
Prevention
Preventing fire blight involves pruning and disposing of infected branches during the tree’s dormant period.
Sterilize pruning tools before and after use and between cuts to avoid spreading the bacteria. Avoiding overhead watering can also help prevent the spread of the disease.
Treatment
Treatment for fire blight involves applying antibacterial sprays such as copper-based sprays or antibiotics like streptomycin.
However, these treatments are more effective as preventive measures rather than curative ones.
7. Root Rot Diseases
Root rot diseases in dogwood trees can be caused by several different fungi, including Phytophthora, Armillaria, and Rhizoctonia.
Symptoms
Symptoms of root rot diseases include yellowing leaves, wilting, and a general decline in the tree’s health. The roots of the tree may appear black and rotten.
Prevention
Preventing root rot diseases involves ensuring good drainage in the soil around the tree. Overwatering and waterlogged soils can create conditions favorable for these fungi.
Ensuring well-draining soil and avoiding overwatering can help prevent these diseases.
Treatment
Treatment for root rot diseases involves improving the drainage around the tree and applying a suitable fungicide. In severe cases, it may be necessary to remove and replace the affected soil.
8. Cankers
Cankers are localized dead areas on the bark of a tree, often caused by various types of fungi or bacteria. In dogwood trees, cankers can be caused by fungi such as Fusicoccum and Botryosphaeria.
Symptoms
Cankers are typically characterized by sunken, discolored areas on the bark of the tree. These areas may be small and localized or can spread to large sections of the tree.
The bark within the canker area often appears darker and may crack or peel.
In severe cases, cankers can girdle branches or the trunk, disrupting the flow of water and nutrients and leading to branch dieback or tree death.
Prevention
Preventing canker diseases involves maintaining the overall health and vigor of the tree. Stressful conditions, such as drought, injury, or poor nutrition, can make trees more susceptible to canker diseases.
Therefore, proper watering, fertilization, and injury prevention can help prevent these diseases.
In addition, pruning and disposing of infected branches during the tree’s dormant period can help prevent the spread of the disease. Be sure to sterilize tools before, during, and after use.
Treatment
Treatment for canker diseases involves removing and disposing of infected branches. In some cases, larger cankers on the trunk can be carefully cut out in a process known as “canker excision.”
This should be done by a professional arborist to avoid causing further injury to the tree. Fungicides are generally not effective against canker diseases once the infection is established.
However, a study found that injected treatments such as Arbotect (a triazole fungicide) and phosphorous acid can be effective in minimizing canker growth in trees.
These treatments likely work by stimulating the tree’s own defense mechanisms rather than by directly killing the fungus.
9. Botrytis Blight
Botrytis blight, also known as gray mold, is a common fungal disease caused by Botrytis cinerea. This fungus thrives in cool, wet conditions and can affect many types of plants, including dogwood trees.
Symptoms
Symptoms of Botrytis blight include brown leaf spots, wilting, and a fuzzy gray mold that develops on the affected parts of the plant. The disease can cause significant leaf drop and dieback.
Prevention
Preventing Botrytis blight involves ensuring good air circulation around the tree and avoiding overhead watering.
Regular cleaning of fallen leaves and debris around the tree can help remove potential sources of infection.
Treatment
Treatment for Botrytis blight involves removing and disposing of infected plant material.
Fungicides containing chlorothalonil or iprodione can be effective for treating Botrytis blight.
10. Crown Gall
Crown gall is a bacterial disease caused by the bacterium Agrobacterium tumefaciens. This bacterium can cause the formation of galls or tumor-like growths on the roots and lower trunk of the tree.
Symptoms
Symptoms of crown gall include the formation of round, wart-like galls on the roots and lower trunk of the tree.
These galls can disrupt the flow of water and nutrients in the tree, leading to reduced vigor and, in severe cases, death of the tree.
Prevention
Preventing crown gall involves avoiding injury to the tree as the bacteria can enter the tree through wounds. This includes careful handling of the tree during planting and maintenance activities.
In addition, using resistant rootstocks can help prevent this disease.
Treatment
Treatment for crown gall is challenging as the galls are often not removable and the bacteria can persist in the soil.
However, some studies have shown that certain nonpathogenic strains of Agrobacterium can be used as a biological control agent to prevent crown gall.
These beneficial bacteria can outcompete the pathogenic bacteria, reducing the incidence of the disease.
Dogwood Pests
Hopefully, you’ll never have to worry about a serious pest infestation on your dogwood, but if you do notice signs of pest activity, it’s important to know what you’re dealing with and how to treat it.
1. Dogwood Borers
Dogwood borers, Synanthedon scitula, are a common pest of dogwood trees. The larvae of these moths bore into the bark of the tree, causing significant damage.
Symptoms
Symptoms of dogwood borer infestation include wilting, yellowing leaves, and a general decline in the tree’s health.
The bark of the tree may show signs of damage, including holes and sawdust-like frass. In severe cases, dogwood borers can cause the death of the tree.
Prevention
Preventing dogwood borer infestations involves maintaining the overall health and vigor of the tree.
Stressful conditions, such as drought, injury, or poor nutrition, can make trees more susceptible to borer attack. Therefore, proper watering, fertilization, and injury prevention can help prevent these pests.
Treatment
Treatment for dogwood borers involves the use of insecticides. The timing of the application is critical, as the insecticides must target the larvae before they bore into the tree.
Therefore, insecticides are usually applied in late spring or early summer when the adults are laying eggs.
2. Dogwood Twig Borer
The dogwood twig borer, Oberea tripunctata, is a beetle that can cause significant damage to dogwood trees. The larvae of this beetle bore into the twigs and branches of the tree.
Symptoms
Symptoms of dogwood twig borer infestation include wilting and dieback of branches. The bark of the affected branches may show signs of damage, including holes and sawdust-like frass.
Prevention
Preventing dogwood twig borer infestations involves regular inspection and pruning of the tree. Removing and disposing of infested branches can help prevent the spread of the beetles.
Treatment
Treatment for dogwood twig borers involves the use of insecticides. As with other borers, the timing of the application is critical and usually coincides with the adult activity period in late spring or early summer.
3. Scale Insects
Scale insects feed on the sap of the tree, leading to yellowing leaves, stunted growth, and in severe cases, death of the tree.
Symptoms
Symptoms of scale insect infestation include yellowing leaves, a sticky residue on the leaves or surrounding surfaces (this is honeydew produced by the insects), and the presence of the scale insects themselves on the tree.
Scale insects are small and often resemble little bumps or scales on the tree’s branches and leaves.
Prevention
Preventing scale insect infestations involves regular inspection of the tree and immediate action when scale insects are detected.
Early detection and removal can prevent the insects from establishing a large population and causing significant damage.
In addition, maintaining the overall health and vigor of the tree can make it less susceptible to scale insect attacks.
Treatment
Treatment for scale insects involves the use of insecticides or horticultural oils like this one. The timing of the application is critical as the insecticides must target the insects when they are in their vulnerable crawler stage.
Therefore, insecticides are usually applied in late spring or early summer when the crawlers are active. In some cases, natural predators such as ladybugs can help control scale insect populations.
4. Dogwood Club Gall Midge
The dogwood club gall midge, Resseliella clavula, is a small fly whose larvae cause the formation of galls on dogwood trees. These galls can cause significant damage to the tree.
Symptoms
Symptoms of dogwood club gall midge infestation include the formation of club-shaped galls on the twigs of the tree.
These galls can cause the twigs to die back, leading to a reduction in the tree’s overall health and vigor.
Prevention
Preventing dogwood club gall midge infestations involves regular inspection of the tree and immediate removal and disposal of any galls that are detected.
This can prevent the larvae from completing their lifecycle and emerging as adult flies.
Treatment
Treatment for dogwood club gall midge involves the removal and disposal of the galls. Insecticides are generally not effective against this pest because the larvae are protected inside the gall.
However, maintaining the overall health and vigor of the tree can help it withstand the damage caused by this pest.
5. Aphids
Aphids feed on the sap of the tree, leading to yellowing leaves, stunted growth, and possibly tree death.
Symptoms
Symptoms of an aphid infestation include yellowing leaves, a sticky residue (honeydew) on the leaves or surrounding surfaces, and the presence of the aphids themselves on the tree.
Aphids are small and often found in clusters on the undersides of leaves or on new growth.
Prevention
Early detection and removal can prevent the aphids from establishing a large population and causing significant damage.
Additionally, maintaining the overall health and vigor of the tree can make it less susceptible to aphid attack.
Treatment
Treatment for aphids involves the use of insecticides or horticultural oils such as neem. The application timing is critical as the insecticides must target the aphids when they are in their most vulnerable stage.
Apply insecticides in late spring or early summer when the aphids are most active. In some cases, natural predators such as ladybugs can help control aphid populations.
6. Dogwood Sawfly
The dogwood sawfly, Macremphytus tarsatus, is an insect whose larvae feed on the leaves of the tree, often defoliating entire branches.
Symptoms
Symptoms of dogwood sawfly infestation include defoliation of branches and the presence of sawfly larvae on the tree. The larvae are caterpillar-like and can be found in clusters on the undersides of leaves.
Prevention
Preventing dogwood sawfly infestations involves regular inspection of the tree and immediate removal of any larvae that are detected.
This can prevent the larvae from completing their lifecycle and emerging as adult flies.
Treatment
Treatment for dogwood sawfly involves the removal and disposal of the larvae.
Insecticides can also be used to control the larvae, but these should be applied when the larvae are young as older larvae are more resistant to insecticides.
7. Japanese Beetles
Japanese beetles, Popillia japonica, are a significant pest of many types of plants, including dogwoods. The adult beetles feed on the leaves of the tree, often leaving a characteristic skeletonized appearance.
Symptoms
Symptoms of Japanese beetle infestation include skeletonized leaves, where only the veins of the leaves remain, and the presence of the beetles themselves on the tree.
The beetles are metallic green with copper-colored wings and are most active on warm, sunny days.
Prevention
Regularly inspect the tree for beetles and signs of their presence. If only a few are found, remove individuals by hand to prevent an infestation.
Treatment
Treatment for Japanese beetles involves the use of insecticides when the beetles are most active in late spring and early summer when the weather is warm and dry.
Closing Thoughts
Dogwood trees can be affected by a variety of diseases and pests. However, with regular inspection, proper care, and appropriate treatment, these issues can be managed effectively.
It’s important to maintain the overall health and vigor of the tree as a healthy tree is less susceptible to disease and pest problems.
If you notice any signs of disease or pest infestation, take immediate action to prevent further damage. In some cases, it may be necessary to consult with a professional arborist or extension service for advice.