Viburnum Branches Dying – Causes and Fix
Viburnum is considered a tough and disease-resistant shrub. However, those that are not well cared-for can become vulnerable to plant stress, which can cause damage to their foliage and stems.
Fungal diseases of the roots and leaves are the most prevalent issues that can kill viburnums. Improper watering, a lack of air circulation, and incorrect lighting levels are all factors that can contribute to weakening these plants, reducing their lushness and vigor. Branches will start to brown as the nutrient supply from the roots is cut off, eventually leading to the collapse of the entire plant.
So, what are the causes of dying viburnum branches? Let us look at the possible contributors, one by one, and learn how we can fix them.
Why are my viburnum branches dying?
1. Botryosphaeria canker disease
Botryosphaeria is a type of plant disease that causes cankers in viburnum branches. This fungal disease generally starts with one dying branch, and gradually spreads through the entire plant.
As the pathogen continues to devour and kill your plant, you might notice the affected stems or branches starting to develop black or dead areas. This is where the fungus is producing fruiting bodies. Eventually, the injury will start to form girdles on the affected branches, cutting the supply of water and nutrients from the roots to the leaves of your viburnum. At this point, the plant loses its vigor and stops producing new leaves until it dies.
How to fix botryosphaeria canker disease:
Unfortunately, treating this disease can be challenging. While you can use fungicides as a preventative measure, there is no cure available to eradicate botryosphaeria. Severely affected viburnums are often best discarded to prevent the disease from spreading to other plants.
Hence, your best chance of winning against the disease is to prevent it in the first place. Pruning back your viburnum might help in most cases, but most importantly, you should nurture your plant properly to ensure that it does not contract the disease.
2. Fungal leaf spots
Fungal leaf spots are caused by fungal spores that thrive in damp, humid environments. These pathogens usually infect viburnums that are watered with overhead sprinklers. The spores cling onto the wet leaf surfaces of the plant, creating small, dark, water-soaked spots. Soon, these spots enlarge as the fungi begin to reproduce, forming bigger necrotic lesions on the leaf tissue. Without proper intervention, the spores can quickly engulf entire leaves and branches of your viburnum, sending the plant to an untimely demise.
How to fix fungal leaf spot disease:
To treat fungal leaf spots in viburnums, consider applying neem oil or copper fungicides to the affected leaves. Make sure to apply the treatment as soon as you notice the symptoms, and repeat the treatment every ten to 14 days until your plant recovers. Because wet environments attract and promote fungal growth, avoid watering the plant from overhead so that you can keep the leaves dry.
For severely infected viburnums, it is best to discard the plants to prevent the fungal disease from spreading. Also make sure to clean and sterilize your garden tools before and after use.
3. Downy mildew
Another type of fungal disease that thrives in damp environments is downy mildew. This plant disease is caused by Plasmopara viburni, and one of its many symptoms is the appearance of angular spots between the leaf veins. Fungal spores can cause the infected leaves to turn brown or red, shrivel, and then die. Another tell-tale sign you might notice is that the undersides of the leaves are engulfed with a white, fuzzy mold.
How to fix downy mildew in viburnums:
The best remedy to keep your viburnums safe from mildew is to practice proper watering. As with other fungal-related issues, wet leaf surfaces can attract fungal pathogens. So, instead of overhead watering, water your viburnums directly in the soil.
Lastly, gather and destroy any diseased leaves and stems from the plant. Do not leave any dead leaves on the ground, especially during the rainy season, as this will allow the spores to spread.
4. Armillaria root rot
Armillaria root rot is caused by fungal spores that mainly attack the shrub’s root system. Early signs might include wilting and yellowing leaves, later followed by stunted growth, leaf drop, and dieback of the stems or branches. Unfortunately, it can be difficult to diagnose Armillaria root rot in viburnums, especially as the symptoms are a bit similar to those of overwatering and other fungal issues.
How to fix Armillaria root rot in viburnums:
Sadly, there are no absolute treatments available for Armillaria root rot. However, you can manage the spread of the disease by removing and burning the infected stems and leaves. Sunlight and air exposure can also help kill the fungal spores present in the soil.
Viburnum leaves can also turn brown and die due to overexposure to sunlight. Leaf scorch or sunburn can affect any shade-loving plants, including your beautiful viburnum shrubs, especially during the hot summer months.
Aside from the sun’s intense ultraviolet rays, dry winds and elevated temperatures can also cause excessive moisture loss from the plant’s leaves. Its roots will also struggle to obtain enough water to supply the drying leaves, resulting in browning leaf tissue.
How to fix sunburned viburnums:
Unlike fungal diseases, sunburn or leaf scorch is not a disease but rather a sign that your plant is in distress. In most cases, the issue can be corrected by moving it to partial shade, or you can add an artificial shade structure to protect your plant’s foliage from the intense summer heat.
The sad news, though, is that the dehydrated parts of the foliage will never return to green, so it is best to prune the damaged parts and wait for your viburnum to recover. Make sure that it receives enough moisture during the hot season to keep it well hydrated.
6. Aphids and thrips
Viburnums can also be assaulted by aphids and thrips. The infestation becomes evident when you notice unusual spots on the leaves, along with other symptoms like black sooty mold, honeydew-like substances on the leaf surface, a silvery appearance on the older leaves, and the presence of tiny insects crawling on the undersides of the leaves.
Pests can weaken and distort your viburnum’s leaves. Green leaves might start turning brown as the tiny bugs feast on their sap. Without proper pest control, aphids and thrips can eventually overrun your viburnums and kill them.
How to fix aphid and thrip infestations:
First of all, the early stages of an infestation can be managed effectively by giving the plant a strong blast of water from your garden hose. This should dislodge most of the insects from the leaves, leaving only a few which you can quickly eradicate with organic treatments. We highly recommend using insecticidal soap or horticultural oils to get rid of adult insects and eggs.
Natural predators are excellent and safe solutions, too. Treat your garden as an ecosystem by adding beneficial insects that enjoy eating aphids and thrips. Some of the natural enemies of these pests include lady beetles, spiders, lacewings, mantises, and wasps.
For severe infestations, chemical pesticides might be your last and only hope. The only downside of this solution is that they also kill beneficial insects. Pesticides are considered toxic to both humans and animals, so use your best judgment before resorting to this method.
7. Viburnum leaf beetle
Viburnum leaf beetles are destructive pests that feed exclusively on the leaves of viburnum shrubs. These invasive insects cause significant damage to the foliage by creating visible bite-holes on the leaves. Long periods of infestation can skeletonize your plant, cause dieback of the leaves and stems, and eventually bring your viburnum to an early demise.
How to fix viburnum leaf beetle infestation:
Both horticultural oil and insecticidal soap have been proven effective in eradicating most of the eggs before they hatch. However, adult insects can be a bit challenging as they tend to be more mobile. The best way to kill the adult beetles is to use contact insecticides such as permethrin, acephate, deltamethrin, bifenthrin, carbaryl, cyfluthrin, or lambda-cyhalothrin.
You can also use systemic products like imidacloprid and clothianidin as soil drenches to control the infestation. However, these chemicals are best applied after your shrubs are done flowering, to avoid harming any beneficial insects.
Can a dying viburnum be saved?
Yes, it is possible to save a dying viburnum, depending on the severity of the damage. First, check the shrub’s branches. If you only see a few browned branches, then your viburnum should bounce back easily. What you need to do is to prune back the dead stems or branches; then make sure to address the underlying issue appropriately.
However, if most of the branches have become brown and brittle, then saving the dying viburnum is probably futile. It is best to discard the diseased plant to protect the remaining healthy plants in your garden.
Seeing your beautiful viburnum on the brink of death can be devastating. Browning or dying branches are caused primarily by fungal diseases, followed by a lack of proper care.
But, do not let this traumatic experience hinder your gardening goals – you might still save your precious shrub with early intervention! If, however, you are too late to save it, you may need to start over with a new plant. Hopefully, in this case, you will have learned through experience how to prevent the same issues in the future.
Image: istockphoto.com / Trygve Finkelsen