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6 Most Common Viburnum Diseases and How to Treat Them

Justice is currently an engineering student and has a passion for doing DIY projects and gardening.

This is a  viburnum davidii plant.

This is a viburnum davidii plant.

What Are Viburnum Plants?

Viburnum plants are popular in yards and gardens, especially during the spring when they bloom. Unfortunately, they’re prone to certain diseases that can affect their health and appearance over time.

These diseases don’t always affect viburnum plants visibly, so it’s important to know how to identify them so you can start treating them early on.

This article will cover some of the most common viburnum diseases and how to treat them, along with additional tips for viburnum care so you can keep your plants healthy year after year.

1. Armillaria Root Rot

One of the most common diseases that affects viburnums is Armillaria Root Rot. This disease is caused by a fungus that attacks the roots of the plant, causing it to rot and die. The best way to treat this disease is to remove the affected plant from the ground and destroy it.

Planting on raised beds can help reduce the spread of the disease because there will be fewer opportunities for infected plants to come into contact with healthy ones. It's also a good idea to avoid planting new plants in an area where Armillaria Root Rot has been present for two or more years. There are no chemical treatments for this type of fungal infection so prevention is key.

It’s important to know how this type of fungus spreads: through vegetative reproduction.

2. Algal Leaf Spot

This disease is caused by a type of algae that thrives in moist, shady conditions. Algal leaf spots appear as small, dark spots on the leaves of the plant. If left untreated, the spots will eventually turn brown and cause the leaves to fall off.

To treat algal leaf spot, remove affected leaves and dispose of them properly. Cut back any overgrown branches to increase air circulation. Spray with fungicide every 10-14 days until no new signs of algal leaf spot appear.

The fungicide must be reapplied after rainfall or heavy watering. There are also preventative treatments for algal leaf spots that can be applied before planting your viburnum, such as organic soil amendments like compost tea and biological fertilizers. These products help suppress the growth of bacteria and fungi that can cause diseases.

For a more natural option, spray plants once a month with garlic extract or use copper-based sprays. These substances inhibit fungal growth without hurting the viburnum's overall health.

It is important to note that all these methods should only be used when there are no visible signs of disease. Once symptoms start appearing, they should not be treated since it may aggravate the problem.

In addition, make sure to give the viburnum plenty of space so it has room to grow away from surrounding trees and shrubs. With the proper care, viburnums can live up to 30 years!

This pathogen is called cephaleuros virescens

This pathogen is called cephaleuros virescens

3. Powdery Mildew

This powdery mildew appears as a white or gray powdery growth on the leaves and stems of the plant. Powdery mildew can weaken the plant and make it more susceptible to other diseases, so it's important to treat it as soon as possible.

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There are a few different ways to treat powdery mildew, including chemical fungicides, horticultural oils, and homemade solutions.

The most common treatments for powdery mildew include either using a good quality liquid horticultural oil (such as Alamo), using your preferred commercial spray fungicide with an oil carrier (such as chlorothalonil) or spraying your plants with water in which you have dissolved bicarbonate of soda at one tablespoon per gallon.

All three methods work well, but they take time to show their effects. If left untreated, powdery mildew will eventually kill the viburnum plants due to weakening them and giving other pests an opportunity to attack them.

My favorite way to stop powdery mildew is to apply something like garden spray or almond oil on the surface of the plant before symptoms start showing up.

Another option is using a natural product such as neem oil or coconut oil diluted with water that has been acidified by lemon juice. All of these are highly effective against powdery mildew, but only if applied early enough to prevent it from occurring in the first place.

This is a Powdery Mildew.

This is a Powdery Mildew.

4. Fungal Leaf Spots

Fungal leaf spots are one of the most common diseases that affect viburnums. These spots are usually circular or angular and can range in color from pale yellow to dark brown. If left untreated, these spots can eventually lead to leaf drop.

To treat this disease, remove affected leaves and dispose of them properly. You can also spray the plant with a fungicide containing copper or mancozeb. Repeat as necessary for best results.

This disease also has a few preventative measures you can take:

  • Pruning out older stems when necessary.
  • Keeping your plant well-watered is also important.
  • Overly dry soil can increase its susceptibility to infection.
  • For better drainage, make sure to not overwater it.

5. Downy Mildew

This disease is characterized by fuzzy, grayish-white growth on the leaves of affected plants. Downy mildew usually appears in late spring or early summer, and can spread quickly if left untreated.

Fortunately, there are a few things you can do to treat this disease and prevent it from spreading.

  • First, make sure to remove any affected leaves from the plant as soon as you see them.
  • Then, mix a solution of baking soda and water together until it reaches the consistency of white glue.
  • Finally, apply the mixture liberally over all infected parts of the plant with a paintbrush or spray bottle.
  • The downy mildew should be gone within two weeks!

On average, downy mildew affects viburnums and their species at least once per year. However, you can minimize its effects by keeping your plants well-watered in dry periods. You should also try to plant viburnums in full sun where possible, as they prefer direct sunlight over shaded areas.

Finally, you can eliminate some disease-carrying mites by thoroughly washing infected branches in lukewarm water every two weeks.

A pathogen that causes downy mildew on cucurbit plants spreads its spores by wind between fields.

A pathogen that causes downy mildew on cucurbit plants spreads its spores by wind between fields.

6. Botryosphaeria Canker

The disease causes cankers, or dead areas, on the stems of the plant. The cankers are often dark in color and may ooze sap. The disease can spread quickly and can kill a viburnum plant if left untreated. Treatment for this disease includes pruning out affected branches and stems and destroying them. Additionally, fungicide can be used to prevent the spread of the disease.

Wounds canker is not common, but it can be found on viburnums. To identify wounds canker disease, look for gray streaks growing in your viburnum’s branches. As time passes, those gray streaks become more noticeable, turning into darkened areas of bark that ooze sap when you touch them.

Wounds canker may eventually spread through your plant; however, its spread is slowed by cutting out affected parts of a viburnum with pruning shears or a knife. If left untreated, a wound canker infection will cause death of the viburnum tree.

Take Care of Your Viburnums

There are a few things you can do to keep your viburnums healthy and prevent disease.

  1. Make sure you plant them in an area that gets plenty of sunlight and has well-drained soil.
  2. Water them regularly, but don't overdo it - too much water can actually lead to fungal diseases. Third, add a layer of mulch around the base of the plant to help retain moisture.
  3. Prune away any dead or diseased branches as soon as you see them.
  4. Finally, consider treating your viburnums with fungicide at least once a year during the hottest months.

Remember that these steps will not only keep them healthy now, but will also help protect them from potential problems down the road. To identify the most common types of viburnum diseases, there's one thing you need to know: they're all related!

Unfortunately, there's no one way to completely avoid all types of diseases since many varieties share some common traits. The good news is that different types tend to show up together on plants.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2022 Justice Ndlovu

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