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Bumps on the Leaves of River Birch — 3 Causes and Remedies

River birch, also known as red birch, is an elegant, fast-growing tree that does best in moist conditions. 

River birches are generally self-sufficient and disease-resistant and, unlike cedar trees which need care, don’t require too much looking after. They often live for more than a century and a half!

That said, these hardy trees are not invincible. 

One of the first signs that a river birch is not in a good condition is the appearance of lumps or bumps on the leaves of river birch.

If you’re concerned because your river birch leaves have gone from being beautiful, delicate, silvery things to looking like they have a case of chicken pox, you’ve come to the right place.

This article will run through the different possible causes of bumps on birch leaves and then discuss how to identify and treat them.  

What are the Bumps on the Leaves of my River Birch?

Bumps on river birch leaves may be light green mite galls that you can treat with pruning and insecticide. Orange pustule-like bumps on the birch leaves’ undersides are caused by fungal rust. Black raised lumps on birch leaves’ tops are sooty mold. The latter two problems are treated with pruning and applying fungicide.

Bumps on the Leaves of River Birch
Bumps on the Leaves of River Birch

Bumps on River Birch Caused by Insects

Bumps on tree leaves caused by gall midges, gall wasps, mites, and aphids are called leaf galls

There are over 1,500 species of insect that cause galls to appear on newly unfurling tree leaves in the early spring. 

Galls are abnormal plant tissue formations that can resemble little balls, knobs, lumps, or warts, depending on the insect responsible for creating them. 

 

Identification

River birch leaf galls are smaller than some other varieties of leaf galls.

The river birch leaf galls are smaller in size compared to other leaf gall varieties and cause green bumps to appear on the leaves' surface
The river birch leaf galls are smaller in size compared to other leaf gall varieties and cause green bumps to appear on the leaves’ surface

They are light green in color when they first appear and are only between 0.2 and 0.8 cm in diameter. 

 

Harmfulness

Specific tree varieties are prone to infestations from specific insects. 

Leaf galls on river birch are caused by an eriophyid mite, which produces wart-like green bumps by feeding off the new leaf growth and then laying eggs inside the emerging galls. 

The leaf galls that cause bumps to appear on the river birch's leaves are caused by the eriophyid mite
The leaf galls that cause bumps to appear on the river birch’s leaves are caused by the eriophyid mite

Fortunately, as with bumps on the leaves of maple trees, the galls are largely a cosmetic issue. 

But, that doesn’t mean you’ll relax while mites nibble your birch leaves to bits.

Follow the treatment recommendations below, which are similar to the recommendations for getting rid of bumps on hibiscus leaves, to get rid of the problem as quickly as possible. 

 

Treatment

If your tree is still young, try to clip away any badly affected leaves and then treat the tree with an organic insecticide. 

Unfortunately, once the galls have developed, you won’t be able to cure your leaves within a single growing season. 

The best thing you can do if you have birch leaf galls is focus on taking preventative measures before the following spring.

In the autumn, when the tree leaves drop, rake them up off the ground and dispose of them in a sealed black bag. 

Then, the following year, treat your tree with a round of a mite-specific insecticide in late February before the new leaf growth appears. 

 

Bumps on River Birch caused by Rust

Rust is a fungal infection that affects trees with lush foliage when the spores are left to fester during periods of rainfall.

Rust is made worse when a tree’s canopy doesn’t get enough air circulation. 

 

Identification

If you notice little orange lumps growing on the undersides of the leaves of your river birch, it probably means that your tree has rust.

You may also see masses of orange spores. 

 

Harmfulness

Rust is not generally life-threatening for river birches. However, it can still be detrimental to a tree’s health and prevent it from thriving. 

If left to spread uncontrolled, this fungus will cause yellow leaves to develop and will lead to leaf drop.

If you leave the orange spores of the rust fungi to spread on the river birch foliage, they will eventually turn yellow and drop
If you leave the orange spores of the rust fungi to spread on the river birch foliage, they will eventually turn yellow and drop

If the situation deteriorates further, your birch may struggle to photosynthesize because there is not enough surface area for a healthy leaf to be exposed to the sun.

 

Treatment

Because rust thrives in a wet or moist environment, try to improve the soil drainage around your affected river birch. 

If the problem worsens over time and the orange spores don’t seem to be clearing, spray your birch leaves with an organic fungicide.

Always follow the specific instructions given for the product you are using when applying anti-fungal solutions. 

To prevent the problem from reoccurring next season, thin out your tree’s upper canopy during the dormant winter period. This method improves the speed at which your birch leaves dry out. 

 

Bumps on River Birch Caused by Sooty Mold

Sooty mold looks just as unfortunate as it sounds.

If black, raised lumps begin appearing on the top of your river birch leaves, your tree may be suffering from sooty mold. 

 

Identification

Sooty mold is a black fungus that grows over and around places where insects have damaged leaves by feeding on them.

As a result, leaves with sooty mold are covered in black, raised lumps. 

Just like what happened to this lemon tree's leaves, sooty mold can cause black, raised bumps to form on your river birch's leaves
Just like what happened to this lemon tree’s leaves, sooty mold can cause black, raised bumps to form on your river birch’s leaves

The mold is feeding on the honeydew left by the insects, so to clear the infection, you need to focus on getting the insects away from your tree. 

 

Harmfulness

If left unchecked, sooty mold can prevent a birch tree from photosynthesizing properly, which can lead to leaf drop. 

However, if treatment advice is followed correctly, river birches with sooty mold can be restored to perfect health over the course of just a single growing season.  

 

Treatment

Check your local horticultural store for an anti-insect tape that can be wrapped around the bottom of trunks of affected birch trees.

Then, use an organic insecticide to treat your birch leaves. 

If the birch in question is small, you could even use a fit-for-purpose eco-horticultural oil to wipe down the leaves.

Follow the application of oil with a damp cloth to keep the oil from burning your leaves. 

Once the insects have left your tree and enough air is circulating through the canopy, the mold will clear on its own accord. 

Conclusion On Bumps on the Leaves of River Birch

The reason for bumps on the leave of a river birch are:

  • Light green mite galls – Treat with an insecticide
  • Fungal rust causes orange pustule-like bumps – Treat with a fungicide
  • Scooty mold cause black raised lumps – Treat with a fungicide

Author Bio

Daniel Iseli

Taking care of houseplants and gardening are my greatest passions. I am transforming my apartment into an urban jungle and am growing veggies in my indoor and outdoor garden year-round.