Diseases That Affect Viburnum
Learn which diseases you should keep an eye out for on your viburnums.
Choose viburnums for a true low maintenance plant. These eye-catching shrubs offer a host of positive attributes, including beautiful flowers, viburnum berries and fall color. For the most part, viburnums are tough and tolerant plants, not plagued by pests or problems. Occasionally, viburnum diseases may strike, but their occurrence is typically rare.
As with nearly any plant, the best way to prevent viburnum diseases is by giving plants ideal growing conditions. For instance, don’t tuck a viburnum into deep shade unless that’s what recommended for it. Adjust soil pH as needed. Most viburnums need soil that’s slightly acid, although some, like Viburnum farreri, thrive in a more acid soil. On the opposite end of the spectrum, arrowwood viburnum (Viburnum dentatum) and Viburnum lantana, including ‘Mohican’ viburnum, tolerate alkaline soil. The bottom line is that you need to know what conditions are best for the viburnums you’re growing.
In general, when growing conditions aren’t ideal, viburnums are more susceptible to disease. The other factor that greatly affects disease development and spread is weather conditions. Certain conditions provide the right environment for diseases to grow, while others halt diseases in their tracks. Most of the viburnum diseases that attack plants are leaf diseases, and the majority of these diseases aren’t intensely damaging to the plants.
Powdery mildew, a viburnum disease caused by a fungus, tends to develop when the weather delivers warm days, cool nights and high humidity. Rain helps to slow this viburnum disease, which is always more severe on plants sited in shade. With powdery mildew, young viburnum leaves and shoots develop a white to light gray fungus covering on leaves. It looks like a light dusting of powder.
To battle powdery mildew, increase air flow around viburnums by removing branches on dense plants to increase air circulation to the center of the plant. Avoid using overhead irrigation, and make sure viburnums — and plants surrounding them — are spaced enough to permit air flow. There are viburnums resistant to powdery mildew, such as Viburnum burkwoodii ‘Mohawk’ and Viburnum carcephalum ‘Cayuga.’
Fungal leaf spots are another common viburnum disease. These leaf spot viburnum diseases usually occur during summer months, when conditions are warm and moist. You’ll usually see the first spots on older leaves. To control the leaf spot viburnum diseases, follow the same practices for powdery mildew control. With both viburnum diseases, rake up and destroy any fallen leaves.