MyWoodlot Health Alert: Sycamore Anthracnose

Brendan Murphy Monday, 14 May 2018

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Driving and hiking around the Catskills and lower Hudson regions this spring, we’ve been seeing a lot of sycamore trees that have lost their leaves. What’s going on? Are they sick? They are, and the culprit is Sycamore Anthracnose.

The telltale signs of this native fungus are springtime sycamore leaves that turn brown and fall off in mid- to late May. The sycamore then responds with bursts of new growth at the ends of branches, like the tree in this photo:

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Why has 2017 been such a bad year for sycamore anthracnose? Blame the weather. The fungus does its best work during cool, rainy springs, which pretty much sums up this year. The rain in particular spreads the fungus, because it disperses the fungus onto the young sycamore leaves.

If your sycamore has lost its spring leaves, is there anything you can do to protect the tree? Well, not really. There are preventive chemical treatments, but they’re not helpful if your tree is already infected. You’ll also need to hire an arborist to apply them.

Fortunately, Sycamore Anthracnose is a native fungus, not an invasive one. Sycamores are used to it and will typically recover from an infection. Your tree may not grow as much this year, but it will probably survive as long as it’s healthy otherwise.

One way to help keep your sycamore healthy is to make sure it’s free of vines and other climbing plants, especially invasives like porcelainberry and oriental bittersweet. When Sycamore Anthracnose hits, the sycamore relies on its trademark pale bark for photosynthesis. Keeping your sycamore vine-free will help it get the nutrients it needs to regrow more leaves.

Another tip if Sycamore Anthracnose hits is to watch under the tree for invasive shrubs like Japanese barberry. The fungus can leave your sycamore with very few leaves for up to a month, which means invasive plants underneath it will get more sunlight. If you have invasives growing beneath your sycamores, do what you can to control those plants to slow their spread.

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