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A cool, wet spring means a big year for fungal diseases on trees and shrubs

May 29, 2019

During cool, wet spring seasons, a variety of fungal diseases affecting trees and shrubs flare up. The symptoms of these diseases are often unsightly and somewhat alarming, and can be a cause for concern for homeowners and woodland owners. This spring is no exception — it’s been quite cool and wet so far (heck it even snowed this May!), and as expected, now that it’s warmed up we are seeing a lot of diseases like tar spot on maple, anthracnose on a variety of hardwood species, and others. 

The good news is that in general these diseases look worse than they actually are. While they can be alarming, they rarely kill trees or cause major damage. In fact, it’s usually not worth treating these diseases even for high-value trees like the ones in your yard. But not all diseases are the same, and some can be serious.

Symptoms to look for

If you’re wondering what’s wrong with your trees this spring, here are a few good resources to consult:

  • Curling or cupping leaves on deciduous trees often are the result of anthracnose diseases. While unsightly, anthracnose diseases generally don’t warrant treatment. You can read more in Extension’s Anthracnose of shade trees webpage.
  • If you have spruces, they are susceptible to a variety of needle cast diseases. Needle cast diseases can be spotted by the discoloration of older needles on spruce, while the current year’s foliage is not affected.

While tree health is on your mind…

You may also be interested in Extension’s fact sheet Emerald Ash Borer in Minnesota and MDA’s interactive map of known Minnesota EAB infestations. While not weather-related, oak wilt and Dutch elm disease are also important fungal tree diseases. Read more at Extension’s Oak Wilt in Minnesota and Dutch elm disease pages.

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