Black Spots on Maple Leaves in Richmond Hill?

In August you notice them: shiny black blotches on your maple leaves, as if someone flicked roofing tar across the canopy. By September half the tree looks spotted. It is a common sight in Richmond Hill, and in nearly every case the cause is a leaf fungus called tar spot.

What Tar Spot Is

Tar spot is caused by fungi in the Rhytisma group. Spores land on new leaves in spring, small yellow spots appear in early summer, and by late summer those spots turn into raised, black, tar-like blotches. The fungus spends the winter in fallen leaves on the ground. In spring it releases spores again, and the wind carries them back up onto the fresh leaves.

Wet springs make it worse, because the spores need moisture to infect leaves. That is why some years look terrible and others hardly show it.

Is It Hurting My Tree?

For a healthy maple, no. The fungus lives on the leaves, and the tree grows a new set every spring. A badly spotted maple can shed its leaves a couple of weeks ahead of schedule, which looks alarming but doesn’t do lasting damage. Tar spot doesn’t spread into the branches, the bark or the trunk.

The exception is a tree that is already in trouble. A maple fighting root damage, drought on sandy soil, compaction from construction or old wounds can feel every bit of extra stress. In that case tar spot is not the main problem, but it piles on.

How to Tell Tar Spot From Something Worse

A few checks separate a cosmetic leaf problem from a tree that needs attention.

• Spots only on leaves. Tar spot stays on the leaf surface. Black cankers, oozing or cracks on the bark point to a different problem.
• The canopy is still thick. If the tree is full of leaves apart from the spots, it is fine. Bare branches at the top, or whole sections that leaf out late, are a different story.
• Leaves are spotted, not scorched. Leaf edges that turn brown and crispy in midsummer point to drought or root stress instead.
• Which maple? Norway maples get it worst. Silver and red maples get it too, usually more lightly. Sugar maples are less affected.

What Actually Helps

The single most effective step is cleanup. Rake up the fallen leaves in fall and put them out with your yard waste rather than mowing them into the lawn or adding them to a backyard compost pile, which often isn’t hot enough to kill the fungus. Fewer leaves on the ground over winter means fewer spores next spring. If your neighbours’ maples are spotted too, it helps if everyone on the street rakes.

Beyond that, keep the tree healthy. Water a young or stressed maple deeply during dry spells, keep mulch a few centimetres away from the trunk, and avoid driving or parking over the root zone. A thinned crown dries faster after rain, which can reduce leaf diseases, but it won’t stop tar spot on its own.

Spraying isn’t something we do. Fungicide on a big maple for tar spot is rarely worth the money anyway, and it takes an applicator with a licence.

Maples in Richmond Hill

Norway maples went in along many Richmond Hill streets decades ago, especially in older neighbourhoods like Richvale and Crosby, and they are the trees most often covered in tar spot. You will also see it on silver maples around Mill Pond and along the creeks. Up north on the moraine, the sandy ground around Lake Wilcox dries out in summer, and for maples there a dry August is a bigger threat than any spots.

A spotted maple on the strip by the curb is usually a City tree. Those are the City’s to look after, so call Access Richmond Hill at 905-771-8800 about them.

When a Spotted Maple Needs More Than Raking

Call us if the spotted maple also has bare twigs high in the canopy, big broken limbs, a split in the trunk, fungus growing near the roots, or a crown that looks thinner every summer. Those are signs of a tree under real stress, and tar spot is only the visible part. Often the fix is clearing deadwood and thinning the crown so the tree carries less weight and gets more air. That is everyday work for our trimming and pruning crew, and we haul every branch away.

Not Sure What You Are Looking At?

Snap two pictures, one close-up of a spotted leaf and one of the full tree, and text them to (289) 475-5822. If it is plain tar spot, Scott will tell you to keep the rake handy and hang on to your money. If the tree has something more going on, we’ll come by that same day, any day of the week between 8am and 8pm, and the quote is free.

Tar spot often shows up alongside other late-summer worries, such as leaves dropping early or a few dead twigs. Seeing several problems at once is the best reason to have someone look at the whole tree rather than just one leaf.