Common Dogwood Problems: Pests And Diseases Of Dogwood Trees

By: Bonnie L. Grant, Certified Urban Agriculturist

Dogwood is a popular ornamental tree with its flowering bracts, elegant foliage, and bright red fruits. These plants are relatively hardy but they do have their Achilles’ heels. We have all heard the fables about how even the smallest can bring down the mighty. This is true with a host of fungal and bacterial diseases of dogwood or tiny insects that may infect or infest your dogwood tree. The issues affecting dogwood trees are too numerous for this writing, but we can cover some of the most common dogwood problems.

Dogwoods need fertile, moist soil with good drainage. They are understory trees and require dappled lighting with protection from the hottest rays of the day. But even plants with good site conditions, annual fertilizer, and adequate water may still encounter dogwood tree problems that destroy their health and vigor.

Diseases of Dogwood

Dogwood anthracnose is one of the most common fungal diseases to attack this plant. It starts out with blighted leaves, showing purple margins, and tan color around the edges of leaves. Secondary signs may include cankers on twigs and smaller branches. These gradually extend to the trunk of the tree with necrotic weeping areas.

Spot anthracnose, septoria leaf spot, and powdery mildew are all conditions that affect the leaves. Root rots and canker disease abound and thrive in moist conditions. There are listed fungicides and bacterial agents to combat the various disease issues affecting dogwood trees. Check with your local County Extension office for help in treatment or contact a certified arborist.

Dogwood Tree Pests

Hardly any ornamental tree is without its fans. Dogwood trees have several insects and their larvae that call the tree their home. Significant loss of vigor and illness can result when these tiny marauders invade in quantity.

  • The dogwood borer is the most noteworthy pest of the tree. Larvae live in the cambium layer and their travel and eating damage the flow of nutrients and water. Often branches can die.
  • Numerous scale insects are dogwood tree pests.
  • The dogwood sawfly larvae feed on the foliage and the dogwood club gall midge causes spindle-shaped swelling on twigs.

In large colonies, the only treatment is pesticide sprays to prevent loss of health in your tree. Read all the directions carefully and use a targeted formulation.

Other Common Dogwood Problems

Dogwoods do not respond well to drought or flooding. They need fertile soil, so in poor soils they will eventually decline. The foliage may burn or turn reddish in summer when there is insufficient water. Use mulch 3 to 4 inches (7.5-10 cm.) deep and 3 feet (1 m.) around the trunk to conserve moisture. Just be sure it doesn’t touch the trunk.

Speaking of trunks, the tree is susceptible to mechanical injury, which will open the gate to insect invasions or fungal issues. Most dogwood tree problems can be avoided by giving adequate care and choosing healthy dogwood varieties that are suited for your area.

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Preventive Care

Provide excellent, consistent care to red twig dogwoods. Appropriate cultural attention is often the only control necessary to prevent the development of canker disease. These trees tolerate wet conditions and adapt to most soil types. But for the healthiest trees, grow red twig dogwoods in areas of the landscape that offer full sun to partial shade and maintain moist, well-draining soil with a pH of 5.0 to 7.5. Red twig dogwoods perform best in U.S. Department of Agriculture hardiness zones 2 to 9.

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.

Anthracnose Identification

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.

Anthracnose Treatment

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.

Canker Identification

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 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.

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.

Comments 2 comments

Have lost 100’s of dogwood in Wa & Or, sad. What zone is corus x rutgersnsis?

I can’t find White Weeping Birch for zone 3 in Helena Montana. Is there any for sale in my area?

Yes, it’s a shame to see it affecting Pacific dogwoods too. The Hybrids are zone 5, which is pretty much the same for all flowering dogwoods. As for White Birch, I would check for the presence of birch borer in your area (ask around, including FDA reps and local horticulture colleges) before planting. It’s a European species and certainly out east not really viable anymore because of borer attack. You might look for native birch instead – Betula nigra for example.

Variants of the Dogwood

Cornus refers to a specific genus, and within the genus are over 50 species of the commonly known Dogwood. These species are divided into four subgenera, or sub-genus species. These sets are determined by distinguishing characteristics of the flowers and bracts[1]. The four main subcategories are:

Flowering Dogwoods (Benthamidia)
Bunchberries or Dwarf cornels (Chamaepericlymenum)
Cornels (Cornus)
Dogwoods (Swida)

Choosing the right Dogwood for your property means considering what your location has to offer and for what you are looking. A symbiotic relationship, where both your Dogwood benefits from necessary water, sun, and nutrient supplies and you benefit from the best height, shade, and beauty of the Dogwood, is in everybody’s interests.

Noteworthy Tips on the Dogwood

– Dogwoods do not usually require a great deal of fertilization skimp on the mulch and meter out the water!

– The name Dogwood comes from the word “dog-tree”, which was introduced into English in 1548.

– Dogwood is also thought to derive from “dagwood”, which would involve using the tree’s thin twigs for creating daggers.

– Chaucer used the term “whippletree” to refer to the Dogwood, which is the name for the piece of wood connecting the horse’s harness to the drag pole of a cart.

– Dogwoods have been used medicinally for generations the bark is rich in tannins, so ground bark or leaves are used to treat pain, fevers, backaches, dizziness, weakness, excessive sweating, uterine bleeding, and incontinence.

[1] Bract – a specialized leaf, usually associated with the reproductive actions of the plant. These “leaves” often sit below the flower or on smaller stems.

Watch the video: Powdery Mildew On Flowering Dogwood - James Blake

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