deciduous leaves

Asked November 4, 2020, 8:35 PM EST

Hi, Our vine maples, bigleaf maples, and kiwi leaves are all just turning brown and staying stuck to the branches. There is no color change. Most of these plants were watered periodically over the summer (in most cases once a week) but other bigleaf maples on our property were not and look the same. Do we have a fungus problem or some other stressor going in in our trees?? Thanks so much! Jen

Benton County Oregon

1 Response

Brown leaves hanging onto trees and other plants this fall - this is something I'm sure a lot of people are wondering about. First, it is unlikely to be caused by a fungus. If you don't see signs of fungal infection, you don't need to worry about that.

In a normal fall, the weather gradually cools, signaling deciduous plants that it is time to stop photosynthesizing. This is what causes many leaves to change color, as the removal of green chlorophyll reveals the underlying colors of the leaves. Then the plants draw out the nutrients from their leaves and put it in storage in their tissues for the winter. Finally, they form what is called an "abscission layer" at the base of each leaf where it attaches to the branch. This cuts off the connection between leaf and tree (or shrub) and the leaf falls.

This year things were a bit different. First, we had the smoke in early Sept., which reduced the amount of daylight plants were receiving for nearly two weeks. Not a lot is known about how this affects plants, but it appears that some plants that use day length to cue their growth patterns thought it was time to shut down for fall. So some plants developed brown, dead leaves back in September.

After this, we had fairly warm fall, and then, very suddenly, a significant freeze around Oct. 27. Many plants were simply not prepared. The freeze killed their leaves, before the abscission layer was formed, and so they hang there, brown but still attached, until they decay enough that a wind can blow them off.

The good thing is, there are many trees that didn't react adversely to either of these events, and are right now displaying their normal glorious fall colors. I hope you’ll get out and enjoy the fall color where you can find it!