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Cornus (Dogwood) pests and diseases
Last Updated on March 20, 2020 by John
Dogwood is a very popular ornamental tree that is known for its elegant foliage and is bright red fruit, you also get the Cornus varieties such as Cornus alba and Cornus sanguinea which are grown for there bright winter stems and pruned back hard in spring.
Cornus are very strong but one downside is the host of diseases that can infest a dogwood tree and cause serious problems no matter how healthy your tree was otherwise. For most people, serious problems are not very common, however, they do however have issues and its worth keeping them in mind.
The best way to prevent some diseases is to provide ideal growing conditions, Dogwoods require moist, fertile soil with optimum drainage, this means not to wet but also keeping the soil moist but not water logged.
They also require dappled lighting and a lot of protection against the hottest sun of the day, this means trying to avoid planting them in open sunny positions to start with. But even if you have the right growing conditions with proper fertilizers and adequate water, you can still come across problems that can have a significant impact on the health of your plant.
Dogwood anthracnose is one of the most common fungal diseases but it only effects the flowering cornus, which include Cornus florida and Pacific dogwoods (C. nuttallii). Kousa dogwood (C. kousa). It does not seem to affect Tatarian dogwood (Conrus. alba) and redosier dogwood (C. sericea).
For those it does affect, it starts with blighted leaves and eventually manifests in the form of purple margins and brown colours along the perimeter of your leaves. After that, you might notice cankers on the small branches too. Eventually, the problem will make its way to the trunk and result in necrotic weeping areas along the trunk.
Spot anthracnose, powdery mildew and septoria leaf spot
Spot anthracnose which mostly affects Cornus florida, powdery mildew which affects most cornus varieties as well as many other plants and finally septoria leaf spot also known as Septoria blight, are all conditions that can negatively impact the leaves. These are best treated to removing effects leaves and spraying with a fungicide. Ideally, if you have been affected by these diseases before, we recommend spraying just as buds start to open in spring to help prevent it again. Ensuring good air circulation can also help prevent these and many diseases.
Root rot and Canker disease
Root rot and Canker disease can take place if you have moist conditions, this means not overwatering and making sure the soil is free-draining. This may mean digging in some horticultural grit into the soil to help drainage, ideally before planting.
To combat all of these it’s best that you use listed fungicides in spring and spray every 7-8 weeks or what the manufactures recommend on the packaging.
- Systemic protection and control of blackspot, powdery mildew and rust
- Use on roses and other flowering or ornamental plants
- Protects new growth and protects plants for over 3 months, when used at intervals recommended in usage instructions
- Use between March to September
- Apply using a garden pressure sprayer washed before and after use
There is no ornamental tree that doesn’t have its downside. Dogwood trees are no exception and there are several insects that can make your dogwood their home so it’s important to treat affected trees quickly to reduce damage.
The Dogwood borer is one of the worst pests you will find. The larvae lay inside of the tree and then eat their way out of the tree taking nutrients and water from it. The result is that the leaves and branches die.
There are a lot of scale insects that can cause problems for your tree too but they are usually not too damaging.
Dogwood sawfly larvae
The Dogwood sawfly larvae live feed on the foliage as well causing a great deal of damage and can nearly strip a tree of all its foliage very quickly.
Treating these pests
If you have a large infestation of any of these pests, the only treatment is to use a pesticide spray as soon as you notice a problem. Always follow directions on the pesticide.
- A contact and systemic insecticide that offers protection against a wide range of pests for flowering plants
- Kills all major ornamental insect pests including whitefly, greenfly, blackfly and other aphids, scale insects, mealy bugs, red spider mites, caterpillars and lily beetles
- Also offers a useful level of control of thrips
- Its systemic action protects treated plants from such pests for up to three weeks
- For use outdoors and in greenhouses and conservatories
Other potential problems
Dogwoods can show signs of distress if there is flooding or drought, again this means water during dry spells and makes sure the soil is well-drained before planting maybe adding some grit to the soil to help with drainage.
They require fertile soil so if the soil conditions change the health of the tree will eventually decline, again before plating add plenty of compost to the soil. You might notice the foliage turning red or burning in the summer if you haven’t watered it enough.
You can help conserve moisture by adding 10 to 15cm of mulch spread out one meter around the base of the plant. Just make sure the mulch doesn’t directly touch the trunk.
Last update on 2020-10-01 at 09:02 / Affiliate links / Images from Amazon Product Advertising API