Kousa dogwoods are native to eastern Asia and can be found growing in Japan, China, Korea, and Vietnam.
That means they know how to handle cold weather!
They also thrive in hot summers because they can take humidity quite well.
The best part is their resistance to pests and diseases.
They are so disease-resistant that you can cut them to the ground in early spring and they’ll grow back healthy as ever.
It’s a great choice for tough urban landscapes because it is tolerant of drought, shade, pollution, salt air, and urban heat island effects.
Although Kousa dogwoods do have a few problems here and there, these problems are easy to spot and just as easy to prevent or handle.
Here’s a list of the top 7 Kousa Dogwood problems from my experience working with these plants:
7. Anthracnose
Anthracnose causes dark lesions on leaves and flowers. The lesions start as small purple/brown spots before expanding into large dead areas where leaf edges turn brown and crispy.
The flowers may exhibit small purple/brown spots on the petals as well.
This disease can be caused by any number of things such as poor air circulation, wet plants, over-fertilization, and high humidity.
Solution
The best way to prevent anthracnose is to ensure good airflow through your plants so that dry winds can sweep spores off the plant before they have a chance to germinate.
Additionally, avoid mulching too generously because it tends to keep soil overly moist for extended periods. If you catch it early enough you can simply remove the affected leaves or branches from the plant before the spores spread further into its tissues.
In severe cases, systemic fungicides may be required this should only happen every other year.
6. Powdery Mildew
Powdery mildew typically appears on new growth in the spring and fall, but it can also occur again later in the summer.
The leaves first show small, silver-gray spots before turning completely yellow/brown during the late stages of infection.
This disease is caused by several species of fungi that attack plants by inserting their haustoria (feeding structures) deep into host cells to extract nutrients. Infected tissues feel powdery due to masses of fungal spores formed within.
Solution
The best way to prevent powdery mildew is to ensure good air circulation through your plants.
This disease thrives in warm, humid conditions so making sure there’s a nice flow of air between your Kousa dogwood and surrounding vegetation will go a long way toward preventing an outbreak.
Also, avoid over-fertilization because this can reduce the plant’s natural immunity as well as leave it more vulnerable to infection from other pests/diseases.
In severe cases, fungicides may be required but only every other year should you see such a need for their use.
5. Leafminers
A leafminer is a common pest in Kousa Dogwoods that feeds by chewing out “mine tunnels,” or spirals, through leaves.
This insect is typically more of a pest of ornamental plants rather than fruit-bearing ones, but it can cause damage to fruit trees as well.
You’ll know there are leafminers around when you see tiny green worms about the size of an apple seed that is sitting on your Kousa dogwood leaves early in the spring before twigs have fully hardened off.
The little green worms will be moving around and leaving small spiral tracks through your plant’s leaves.
Solution
The best way to prevent leafminers is to monitor for their presence early in the spring before they do any harm by checking the undersides of new growth for larvae activity.
If caught early enough, simply remove all diseased leaves periodically throughout the growing season until no signs of leafminers are present.
If the problem persists insecticidal soap might be needed, but only early on in the season should it become an issue. Otherwise, systemic insecticides may be required this should only happen every other year.
4. Aphids
Aphids suck juices from plants by inserting their needle-like mouthparts into phloem cells where they extract sap using a straw-like structure called a “proboscis.”
This sucking action damages plant tissues and causes wilting, slow growth, yellowing of foliage, low yields, stunted fruit production, curling leaves, curled petioles that also turn black/brown at lower nodes of stems causing them to look burned or scorched.
Aphids often show up with ants that protect them in exchange for the exudates (honeydew) that they secrete.
Solution
The best way to prevent aphids is to maintain healthy plants, especially during the fall when stressed plants are more vulnerable than ever before.
Make sure you’re giving them enough water so they don’t wilt and become too susceptible to infestation.
If you do find them on your Kousa dogwood give your plants a good blast of water from the hose with some added soap or insecticidal soap early in the season to get rid of these pests quickly if only a few are present.
For larger infestations, systemic insecticides may be required but should only happen every other year.
3. Tree Topples Over And Dies From The Top Down
Kousa dogwoods are very sturdy trees when young, but this changes with age. They get top-heavy and can easily be blown over in a storm or strong wind.
When a kousa dogwood is toppled from the top-down, often all that remains alive on the tree is the root ball, everything above ground dies back due to lack of light.
Solution
There is no easy solution to this problem because once these trees get too large for their space they need to be removed and replanted into a larger area.
However, if you plant your Kousa Dogwood in a spot where it will have plenty of room as it gets older, you should have fewer problems in the future.
2. Viral Diseases
Viral diseases that typically affect Kousa Dogwood plants include Cucumber Mosaic Virus (CMV), Raspberry Bushy Dwarf Virus (RBDV), and Verticillium Wilt (Vert).
All of these viruses infect plants through insect vectors like aphids or leafhoppers; major sources of disease spread among ornamental plants throughout regions plagued by these insects.
Solution
The best way to prevent and manage these viruses is to remove any diseased plant material in the fall. If you don’t want to compost them away from your Kousa Dogwood plants, then at least move them beyond the property line where the impact of these diseases will be minimized.
1. Verticillium Wilt (Vert)
Verticillium wilt is caused by a soil-borne fungus that exists throughout most soils of landscapes and vegetable gardens alike.
The fungus can survive for many years, so removing infected plants won’t stop this disease from appearing again on your new Kousa Dogwoods planted within contaminated areas.
Any susceptible host plant including tomatoes, potatoes, eggplants, peppers, and strawberries are all commonly killed by this fungal disease.
Solution
The best way to control Verticillium wilt is by planting Kousa Dogwoods in raised beds with good drainage and deep loamy soils that are not compacted.
Ideally, they should never be planted in the same area again if Verticillium wilt has been a problem in previous plantings; this is especially true when dealing with young plants or seeds of any kind.
When to plant
Plant your Kousa Dogwood from mid-fall through early spring (October–April). Avoid planting during the hot summer months (June – August ).
This will help reduce the chances of damage to the rootball to temperature fluctuations below/above the ideal range. Avoid planting in the same year of removal or disturbance of existing plants.
Planting location
Dig a hole that is twice as wide, but not quite as deep as the root ball.
Make sure there are no rocks at the bottom of the hole. Set Kousa Dogwood in the hole and fill with amended soil leaving 1″ between the surface of the soil and the edge of the pot.
Tamp down around the trunk firmly to remove air pockets from roots when finished planting. Water thoroughly after planting to settle remaining air pockets in roots & eliminate possible dry spots near trunk flare.
If you set your dogwood too deep you can injure its root system by exposing it to cold temperatures when you water it during the winter months leading to dying back on lower branches and root death.
Watering
Water your Kousa Dogwood deeply once a week during the first growing season (April–October). During times of drought water every 7 to 10 days.
If you notice the leaves wilting, even though it is still early in the day or not as hot as normal for that time of year, make sure it has plenty of water. Allow the top 2 inches of soil to dry out between watering.
Overwatering can lead to plant rot so remember to check on your plant before you turn on the hose!
Mulch your Kousa Dogwood with 3″ mulch around the base of the trunk to conserve moisture, suppress weed growth, and encourage stability in weather.
Fertilizing
Fertilize Kousa Dogwood in early spring as new growth begins with a complete fertilizer such as 15-15-15 or 10-10-10.
Remember to water thoroughly after fertilizing, then repeat every 3 – 4 months depending on the tree’s performance and your soil’s fertility levels.
Pruning/shaping
Prune any dead branches and thin out large branching at the base of the tree to improve air circulation & make sure the center is open for good light penetration.
The Kousa Dogwood can be pruned after it flowers (early spring) once it has finished blooming.
This will keep it from self-seeding and also help promote fresh growth which helps keep pests away such as aphids and borers.
Pests
Kousa Dogwood can fall prey to a few common pests such as borers and aphids. Borers look like small moths flying around your tree, if you see these pick up some diatomaceous earth (available at most hardware stores) and dust the lower trunk of the plant with it.
This will kill off any larva that might be living in there! Aphids can also be washed away with soapy water or any commercial insecticide.
Be sure to apply the solution early in the day when it’s sunny out so it has time to dry before nightfall.
Conclusion
The common problems that plague the Kousa Dogwood (Cornus kousa) are discussed above; however, it is important to note that there is no single method of solving all of these problems.
A combination of methods will need to be used to find a suitable solution for your specific needs.
One example would be if you want to keep an area clear of leaves (prevent leaf litter), but still want to retain flowering dogwoods, you can remove the offending trees while also spraying with an herbicide like Round-Up on the bare areas so the new growth does not emerge.
Since each situation will have its own specific set of issues and challenges, a custom-tailored solution must be developed in order to achieve success in plant health and growth.