Pieris Forest Flame Diseases – what to look out for and how to treat them

Pieris Forest Flame Diseases – what to look out for and how to treat them

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Fungal Leaf Spot

Pieris Forest Flame is the most popular variety of pieris grown in the UK. From the bright red leaves and white bell-like flowers in the spring, the leaves go through colourful changes from red to pink to cream to green during the growing season. But if your Forest Flame leaves are looking a bit sickly, there’s probably one main culprit – the disease of Fungal Leaf Spot.

Does your pieris forest flame have fungal leaf spot?

To find out if your shrub has this common disease, just get down close to the leaves and look for brown spots on them. These spots start out small, then get larger and larger. Then, eventually the leaf falls off. You may need to turn the leaves over to look at the underside of them to find these ugly spots.

Fungal leaf spot disease arises when fungal spores in the air land on a warm and wet plant surface. Settling into their comfortable new home, the spores start to reproduce and the brown leaf spot starts to grow.

What to do about this pieris disease?

Care and attention

As always, it’s better to catch the disease in its early stages. Regularly examining your Forest Flame leaves is a way to detect the brown spots when they’re at the tiny stage.

As the fungus needs warm and wet conditions to flourish, ensuring good air circulation throughout the plant and keeping it dry will make it inhospitable to the spores in the first place.

Make sure to water at the base of the shrub so no water splashes on the leaves. Watering in the early morning allows the plant to absorb the water and dry out before the day really starts.

Keep the base of the shrub clear from weeds and other plants so that air can get between the branches and circulate. Although pieris Forest Flame don’t need much pruning, be sure to remove some branches if they start to crowd together in the shrub. You can learn more about pruning Pieris here

When you mulch your pieris in springtime, keep the mulch away from the trunk of the shrub. When the mulch rots, it won’t make the pieris trunk all wet and warm.


You can try a natural treatment before resorting to a fungicide. It’s better for the Forest Flame and for the environment in all its forms. Remove the affected leaves first. Then mix ½ teaspoon of baking soda into 4L of water and spray that on the remaining shrub.

If that doesn’t work, then use a commercial fungicide to kill all the spores remaining on the leaves of the plant, a general garden fungicide will do the trick.

But it could be Phytophthora Root Rot

Phytophthora Root Rot

If, after examining your pieris leaves, you don’t find any brown spots, check the color of the entire leaf surface. A rare disease that affects pieris Forest Flame is Phytophthora Root Rot. This turns the leaves and some of the rest of the plant yellow and then sometimes purple.

Phytophthora Root Rot is a fatal disease so there’s nothing you can do to treat it. It appears on waterlogged plants so make sure that the soil the shrub is in is well-drained. And don’t over-water and leave standing water around the base of the trunk. Remove the affected branches and hope that this disease hasn’t spread to the rest of the shrub.

I also have an article which covers other pieris leaf problems here and another articles with cover other Pieris plant problems in general here. If your Pieris is losing its leaves you can also learn more about that here.

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