Oak Wilt

This is a hyper-aggressive fungal disease that shuts down a tree’s water-carrying vessels. It’s essentially a cardiac arrest for oaks. Once a Red Oak is infected, it can lose all its leaves and completely die in as little as a few weeks. It spreads both through underground root systems to neighboring trees and via beetles attracted to fresh pruning wounds.

• What to look for: Sudden wilting and rapid leaf drop in mid-to-late summer. Leaves typically turn a dull bronze or brown starting at the outer edges and moving inward toward the stem.

Dutch Elm Disease (DED)

You might think this old enemy disappeared decades ago, but Dutch Elm Disease has made a massive comeback in Minnesota. Carried by tiny elm bark beetles, this fungus clogs the tree’s vascular system, starving it of moisture and nutrients.

What to look for: “Flagging”—where a single upper branch suddenly develops yellowing, wilting leaves in late spring or summer while the rest of the tree looks perfectly healthy. The branch quickly turns brown, and the infection works its way down the trunk.

Emerald Ash Borer (EAB)

Decline While technically an insect infestation rather than a disease, EAB acts like a terminal illness for untreated Ash trees. The adult beetles do minor damage, but their larvae chew winding S-shaped tunnels right beneath the bark. This cuts off the tree’s food and water supply, killing 99% of infected, untreated ash trees within a few short years.

• What to look for: Thinning canopy at the very top, vertical bark splitting, heavy woodpecker activity (as they strip bark to eat the larvae), and small, D-shaped exit holes on the trunk.

Bur Oak Blight (BOB)

This is a native fungal disease that has become significantly more severe due to warm, wet spring weather. It targets Bur Oaks specifically, weakening them year after year until secondary pests like the two-lined chestnut borer move in to finish the job.

• What to look for: Purple-brown, wedge-shaped dead spots forming on leaves in late July and August. The leaves die but remain tightly attached to the branches all winter long instead of dropping naturally.

Rhizosphaera

Needle Cast If you have a Colorado Blue Spruce or other evergreen that looks like it’s dying from the bottom up, this fungus is the likely culprit. It thrives in humid conditions and dense canopies, choking out the needles until the tree looks thin, hollowed-out, and completely bare at the base.

• What to look for: Second-year needles turn a distinct purplish-brown color in spring and early summer, then drop off entirely, leaving only the brand-new growth at the very tips of the branches. Spotting the Signs: How to Identify Tree Stress Diseases rarely strike out of nowhere; they take advantage of trees that are already stressed out by our brutal winters, summer droughts, or soil compaction. Keeping your trees healthy starts with knowing what a stressed tree looks like. Keep an eye out for these early warning signs:
• Premature Leaf Drop: Shedding leaves in July or August is a cry for help.
• Stunted Leaf Size: New leaves that look tiny, pale, or yellowish compared to previous years.
• Epicormic Sprouting: A sudden explosion of fuzzy, small twigs growing directly out of the lower trunk or base of the tree. The tree is trying to compensate for a dying canopy up top.
• Deep Trunk Cracks or Oozing: Liquid weeping from the bark or deep fissures that expose internal wood. Why Timing is Everything: The High Stakes of Delaying Treatment The Golden Rule of Tree Health: It is infinitely easier, cheaper, and safer to invest in preventative care early than it is to deal with a hazardous tree removal next to your roof.

When you ignore a sick tree, you aren’t just letting a plant die—you’re creating a serious liability.

• Hazardous Tree Risks: Delaying preventative action until a tree is past the point of saving means you’re locked into dealing with a heavy, unstable, and hazardous tree removal.
• Safety Hazards: Dead trees dry out fast, becoming incredibly brittle. In Minnesota, a sudden thunderstorm or winter blizzard can easily drop dead, heavy limbs directly onto your house, car, or power lines.
• The Neighborhood Domino Effect: Diseases like Oak Wilt and EAB don’t stay contained. If you let an infected tree sit on your property, the pathogens will actively migrate through the soil roots or air to kill your other trees—and your neighbors’ trees, too.

Why You Need a Professional Tree Care Specialist You wouldn’t try to diagnose a complex medical condition using an online search, and your mature trees deserve the same respect. Tree biology is complex. Misdiagnosing a tree issue can be fatal. For example, treating a tree with the wrong method or pruning an Oak during the high-risk spring transmission window can actually accelerate its death. When you bring a certified tree care specialist from

Above All Tree Service out to your property, we look at the whole picture. We evaluate the health of the tree, measure the structural integrity of the wood, and create a targeted, scientifically backed care plan. Whether it’s structural pruning or canopy management, we catch the problem before it turns into a costly emergency.

Don’t wait until your canopy starts thinning. Get ahead of the season and give your property the protection it deserves.