How do you treat viburnum fungus?

Viburnum Fungus Got You Down? Here’s How to Fight Back!

Viburnums! Aren’t they just gorgeous? These shrubs can really bring a landscape to life. But, like anything else in the garden, they can run into trouble. And when that trouble comes in the form of fungus, well, it’s time to take action. Don’t worry, it’s usually manageable. Think of it like this: a little TLC goes a long way.

So, what nasties are we talking about? Let’s get familiar with the usual suspects.

Know Your Enemy: Common Viburnum Fungal Diseases

First things first: you gotta know what you’re dealing with. Spotting the problem early makes a HUGE difference. Here are some of the most common fungal foes your viburnum might face:

• Powdery Mildew: This one’s pretty easy to spot. Imagine someone sprinkled powdered sugar all over your viburnum’s leaves and stems. That’s powdery mildew! It’s caused by a fungus, Erysiphe viburni, and it LOVES warm days, cool nights, and humid conditions. Shady spots with poor air circulation? Prime real estate for powdery mildew. The good news? Some viburnums are tougher than others. Varieties like Viburnum burkwoodii ‘Mohawk’ and V. carlecephalum ‘Cayuga’ are like, “Powdery mildew? I don’t think so!”

• Downy Mildew: Now, don’t confuse this with powdery mildew. Downy mildew is sneaky. You’ll see light green spots on the top of the leaves, but the real action is happening underneath. Flip the leaf over, and you’ll find a grayish-white, downy fuzz. Those spots will get bigger, turn reddish, then brown as the leaf tissue dies. Plasmopara viburni is the name of the game here, and it spreads like wildfire in cool, wet weather. If you don’t get it under control, your viburnum could lose a lot of leaves.

• Fungal Leaf Spots: This is kind of a catch-all. Several different fungi (Cercospora, Phoma, Phyllosticta, to name a few) can cause spots on viburnum leaves. These spots are usually angular or irregular, and the tissue inside looks sunken and dry. They can start small, but they can merge together and turn reddish or grayish-brown. I usually see these pop up during the summer when it’s warm and humid, and they tend to hit the older leaves first.

• Anthracnose: Think black, sunken spots. That’s anthracnose, caused by Colletotrichum species. It can also cause leaf spots and make your viburnum drop leaves way too early. Not a good look.

• Algal Leaf Spot: Okay, this one’s a bit different. It’s not technically a fungus, but algae! It shows up as green, orange, or reddish-brown spots on the leaves. They might look a little raised and have feathered edges. Cephaleuros virescens is the culprit, and it loves cool, moist conditions. It spreads through wind and splashing rain, so watch out!

• Botryosphaeria Canker (Dieback): This is a nasty one, and it usually targets viburnums that are already stressed out – maybe from drought, injuries to the bark, or bad pruning. The fungus (Botryosphaeria species) gets in through wounds and starts killing the branches. You’ll see leaves wilting and browning, branches dying back, and little black bumps on the bark. I’ve seen this take out entire shrubs, so it’s important to catch it early.

• Armillaria Root Rot: Ugh, root rot. This one’s a killer. Armillaria mellea attacks the roots, causing them to rot away. The symptoms are pretty grim: stunted growth, yellowing leaves, thinning foliage, and eventually, death. If you dig around the base of the plant, you might see white, felt-like fungal growth on the roots. Not a pretty sight.

Time to Fight Back: Treatment and Control

Alright, enough doom and gloom. Let’s talk about what you can DO about it!

The Bottom Line: Prevention is Better Than Cure

• Keep ‘Em Healthy: A healthy viburnum is a happy viburnum, and a happy viburnum is less likely to get sick. Give it the right amount of sunlight, well-drained soil, and fertilizer.
• Keep an Eye Out: Check your viburnums regularly for any signs of trouble. The sooner you spot a problem, the easier it will be to fix.

So, there you have it! With a little knowledge and a little effort, you can keep your viburnums healthy and beautiful for years to come. Happy gardening!