Friday, October 19, 2018

Andrew Dowd

Tar spots on maple leaves seen throughout Eau Claire

Raking helps reduce odds that the aesthetic malady will return

  • IMG-0194

    Maple leaves with black spots on them remain on trees on Nov. 10 in Eau Claire. Tar spot disease is caused by fungi that several maple tree varieties are susceptible to. The disease is mostly cosmetic and can be dealt with by getting rid of the fallen leaves to reduce the amount of fungi around the tree.

    Staff photo by Andrew Dowd
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Instead of waking to fiery red leaves on the maple tree outside my window on autumn mornings, I’ve been greeted with green leaves marred by black tar spots.

A fungus that enjoys water, which we’ve gotten plenty of in recent growing seasons, grew in my maple tree and many others in Eau Claire.

Weather made for a short-lived and somewhat lackluster fall foliage display this year in the Chippewa Valley and the infected maples with their ugly spots didn’t help. 

I’ve seen a fair amount of the tar-spotted leaves hanging from maple trees along sidewalks and in parks lately.

Todd Chwala of the city’s Parks, Recreation and Forestry Department said his crews also noticed maple tar spot this season in trees around Eau Claire. It’s not normal around here, he noted, but also not uncommon to see more of it with wet growing seasons.

Ugly, but OK

To my relief though, maple tar spot is an aesthetic concern but doesn’t harm the tree’s overall health, according to several articles I read online about the disease. The fungus and resulting gross polka dots on the leaves are supposed to go away in following seasons.

To up the odds the spots won’t come back, the articles said the fallen maple leaves should be raked up so the fungus in them won’t linger around trees.

Benjamin Polzin of Down to Earth Garden Center agreed with that advice.

“It overwinters as a spore in the soil, so if you get rid of the leaves, the chances of having that spore winter there is much less,” he said in an email.

Beyond that, for me and many others with maples bearing tar spots, the only thing to do is hope for better looking foliage next year.

There’s “no real acute strategy to manage an aesthetic malady,” Chwala said.

Case for variety

Maples are among the most abundant trees in the city’s urban forest after two other kinds of trees suffered from diseases that weren’t just leaf-deep.

Dutch elm disease has been decimating trees in the U.S. for decades. I had a few elms removed in my yard this summer — one dead from the fungus, a couple others headed in that direction.

Ash trees are being proactively replaced in the city as the emerald ash borer has arrived in our area.

In the wake of these diseases impacting common trees, the city now plants a greater diversity of trees on public land and encourages residents to do the same.

It’s a long-term strategy to prevent an abundance of one kind of tree, only for that variety to be hit by a disease and wipe out a large portion of Eau Claire’s greenery. Though not intended for it, that same rationale works for reducing the impact of aesthetic diseases that effect only specific kinds of trees.

But for now, I’ll just get rid of the ugly leaves and hope that’s enough to improve the look of my maple tree next year.

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