4 Common Spring Tree Fungi in Minnesota
Spring is a time of renewal for Minnesota trees, but it also brings the perfect conditions for tree fungi to thrive. If you’ve ever noticed curling leaves, dark spots, or early leaf drop, your trees may be dealing with a fungal infection. But, by knowing what to look for and how to manage these diseases, you can help keep your trees healthy all season long.
1. Anthracnose
Anthracnose Disease is a fungal infection that thrives in cool, wet spring weather (50-68°F). It causes distorted leaves and leaves to drop but rarely inflicts lasting damage to the tree.
Signs of Anthracnose include:
- Tan or brown leaf spots
- Leaves may curl, cup, or appear deformed
- Lower and inner branches are usually affected the most
What Causes Anthracnose?
The Anthracnose fungus overwinters in buds, twigs, and fallen leaves. Come spring, it then spreads through wind and water splashes to infect new leaves and continue the cycle.
Anthracnose Treatment & Prevention
While this fungal disease is not often deadly, there are ways you can help avoid it. These efforts include:
- Raking and destroying fallen leaves before winter
- Moving any watering or sprinklers that keeps the leaves wet
- Fertilizing only if necessary to keep the tree strong
Even though Anthracnose Disease can look severe, it’s usually not fatal, and most trees recover on their own.
2. Dutch Elm Disease
One of the most well-known tree fungal diseases, Dutch Elm Disease, is caused by the fungus Ophiostoma novo-ulmi. It spreads quickly and can kill an elm tree within 1–2 years.
Dutch Elm Disease symptoms include:
- Wilting, yellowing, and browning leaves (starting at the outer crown)
- Premature leaf drop in spring and summer
- Brown streaking beneath the bark near infected branches
What Causes Dutch Elm Disease?
Dutch Elm Disease spreads in two ways:
- Elm Bark Beetles – The beetles carry the Dutch Elm Disease fungus as they feed and breed inside elm trees, contaminating them as they go.
- Root Grafts – The disease also moves from one tree to another when their roots are connected underground.
Dutch Elm Disease Treatment & Management
- Early pruning of infected branches can slow the spread
- Fungicide treatments may help protect healthy trees
- Removing the severely infected trees, and debarking, chipping, or burning the wood to prevent further spread
- Replacing and replanting with Dutch Elm Disease-resistant elm varieties.
If you notice signs of Dutch Elm Disease, quickly contacting professionals is key to saving your tree and protecting nearby elms.
3. Apple Scab
Apple scab disease is the most common fungal disease affecting Minnesota apple and crabapple varieties. The Apple scab fungus, Venturia inaequalis, thrives in wet spring conditions and can make your fruit inedible.
Apple Scab symptoms include:
- Round, olive-green leaf spots that turn brown or black
- Yellowing leaves that drop by mid-summer
- Olive-green spots on fruit that become corky and deformed
What Causes Apple Scab?
The Apple Scab fungus overwinters on fallen leaves, and spreads to new leaves, flower, and fruit in the spring by the wind and rain. This fungus requires moisture to establish, making wet conditions a major risk factor.
Apple Scab Treatment & Prevention
- Cleaning up fallen leaves—raking and removing to eliminate spores
- Spacing trees properly and pruning for good airflow helps keep leaves dry
- Planting Apple Scab-resistant crabapple varieties
If you see signs of Apple Scab, take action early to reduce fruit damage and protect the other apple trees in your area.
4. Oak Wilt
Oak Wilt is a fatal disease caused by the Bretziella fagacearum fungus. It is most severe in red oak species, where it can kill a tree in just a few weeks. Whereas with white oak species, the fungus may slowly spread across the tree over years before it becomes fatal.
Oak Wilt symptoms include:
- Leaves turn brown at the edges with green centers
- Wilted leaves dropping, starting at the top of the tree
- Peeling bark and fungal mats may appear on the tree trunk
What Causes Oak Wilt?
Oak Wilt season begins in spring when beetles carry spores from infected trees to fresh wounds. The disease also spreads underground when tree roots connect, contaminating nearby trees.
Oak Wilt Treatment & Management
- Avoiding pruning oaks during Oak Wilt season (spring & summer)
- Severing root connections between infected and healthy trees
- Fungicide injections may help protect high-value trees.
- Removing and properly handling the wood to prevent further spread
If you notice signs of Oak Wilt, act fast—Oak tree fungus can quickly devastate entire stands of oaks.
Stay Ahead of Spring Tree Fungi
Minnesota’s cool, wet springs create the perfect environment for tree fungi to spread, but with proper spring tree care, you can protect your trees from serious damage. If you notice the symptoms of any of these tree fungal diseases, contact our experts today!