Research brief: Beech leaf disease threatens NH forests

Beech leaf disease may be the biggest problem facing New Hampshire forests that you’ve never heard of.

To say it’s spreading quickly is an understatement. First detected in Ohio a mere 13 years ago, the disease reached New Hampshire in 2022 and was found in College Woods the following year.

“Now almost every beech tree in College Woods is affected, and we haven’t found any consistent patterns of resistance,” says Jeff Garnas, associate professor of natural resources and the environment, who is studying the impact of the disease with funding from the NH Agricultural Experiment Station. “It may eventually hit all of them.”

Beech leaf disease is caused by a tiny invasive worm called a nematode. Nematodes are well known for causing plant diseases, but most are soil- and root-based. The nematodes that cause beech leaf disease are found far above ground level, and their rapid spread from west to east indicates that they move on the wind.