The horse chestnut trees in yards around the North Shore may look like rust-tinged shadows of their normally lush-green selves, but experts say the prognosis for the plants is much better than their bedraggled appearances.
“I’ve definitely had some calls, people wondering if they’re imagining things or if there really is a problem,” said Kevin Sorby, a forester with the village of Wilmette. “I tell them they’re not imagining it, but that it’s not too bad of a problem.”
Area experts said the trees are being unusually affected by a fungus known commonly as leaf blotch (and more scientifically as Guignardia blotch) but they will most likely survive, and thrive, to bloom next year.
Leaf blotch regularly affects horse chestnuts when the right weather conditions hit, and this year’s wet June and subsequent hot weather provided a nurturing environment for the fungus’s spores, said Tom Fritz, a plant health care specialist and arborist with the Chicago Botanic Garden.
“We seem to see this every summer, but it’s a little more extreme this year, due to the fact that we had very wet conditions at the beginning of the summer,” Fritz said. “One of the saving graces is that usually it doesn’t affect the health of the tree. It’s more an aesthetic problem.”
Fritz said the botanic garden has 30 to 40 horse chestnut specimens on site.
Arborists and foresters in several suburban communities say they’ve heard concerns that the horse chestnut – the aesculus hippocastanum – are looking ominously unhealthy, shedding their seven-lobed leaf clusters far earlier than normal, the leaves transformed from green to dry red-brown before they fall.
The dying leaves make affected horse chestnuts noticeable. The blotch also affects buckeye trees, their close relatives, according to experts. That has led some worried tree lovers to call their local arborists.
The tree boasts perfume-heavy spring blossoms and autumn crops of green-rinded brown nuts, making them standout ornamental additions to the North Shore’s suburban treescape.
Sorby and Fritz both noted that the horse chestnuts, planted by European settlers and Victorian-era fans of the tree, aren’t all that common in the Midwest, at least not on public parkways. They are more often found in private yards, Sorby said.
In Wilmette, Sorby estimated that only one in 200 of the village’s 17,000 parkway trees are horse chestnuts.
Horse chestnuts – not to be confused with the American chestnut tree – are lovely to look at, but not very hardy, both he and Frtiz said. Highland Park city forester Joe O’Neill seconded that estimation.
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“They don’t make terribly good street trees. They are shorter-lived and do have some decay issues,” O’Neill said. “For parkway trees, we want something a little hardier.”
Their relative rarity means that municipalities and private owners have some leverage in preventing leaf blotch from becoming an annual problem on their horse chestnut trees. That can be done, experts say, by raking up and disposing of blotch-infected leaves, thus depriving the fungus spores of a place to survive in the winter.
Fritz added that pruning the trees is important.
“Open up the canopy and let the sun in and the heat to prevent moisture,” he said.
Those measures would be a lot more difficult with more populous species, Sorby said.
“If you clear up your tree, but your neighbor doesn’t get rid of his leaves, the problem remains,” he said, “but with chestnuts, you might have one, and the next one’s a block or two down. It gives you some room to work.”
Winnetka forester Jim Stier offered some advice for lovers of horse chestnut trees, Ohio buckeyes and the rest of the aesculus family.
“Don’t panic,” he said. “They look worse than they are.”
Twitter: @pioneer_kathy