Fungal Disease Turns Aspen Leaves Brown

Oct 6, 2015

Orange and gold leaves usually fill the branches of Aspen trees this time of year. But as Arizona Public Radio’s Aaron Granillo reports, a fungal disease is turning some of those leaves brown and blotchy across the Southwest.

A heavily infected leaf on the Apache-Sitgreaves National Forests
Credit US Forest Service/Apache-Sitgreaves National Forests

The fungi, known as Black Leaf Spot, actually develop every spring, when the leaves first bloom. The main difference this year is the weather, said James Jacobs, a plant pathologist with the US Forest Service. 

“We had a lot of spring moisture, which can be conducive to disease build-up. And this fungus tends to like moisture at certain times followed by warm weather and so we had that,” said Jacobs.

James says additional rainfall this summer combined with monsoon winds splashed the fungi over new

Credit Us Forest Service/Apache-Sitgreaves National Forests

 Aspen leaves, mainly in the Coconino and Apache-Sitgreaves National Forests. As a result, some of the leaves now appear brown, while others have already fallen. Jacobs says there could also be other factors affecting the fall foliage.

“There’s a bunch of variables involved. There’s some insects that can defoliate trees. And, so it’s hard to separate out disease defoliation from insect defoliation,” said Jacobs.

Black Leaf Spot is the most common type of disease found on Aspens in Arizona and New Mexico. But, Jacobs says it’s rare for the fungi to have any long-term effects on the trees.