Last summer, I looked up and noticed something strange about the sugar maple tree that shades my favorite picnic table. Many of the leaves were brown on the margins.
Last summer, I was walking around the parking lot, meandering and looking around after a morning spent at the desk when I looked up and noticed something strange about the sugar maple tree that shades my favorite picnic table. (It’s my favorite picnic table specifically because it is shaded handily during the lunch hour by this maple tree.) Many of the leaves were brown on the margins. Not every leaf on the tree, but seemingly in bunches all over the tree with no definite pattern. I found a fallen leaf on the ground to investigate.
Adjacent leaves with and without scorch
Fallen leaves to investigate
My stretching time was over so I walked in with my leaf and asked a colleague if they had any idea what it might be. “Anthracnose?” they suggested. An excellent place to start.
It turns out anthracnose, which is a fungus, causes leaves to brown along the leaf veins. It wasn’t the culprit here as the margins were clearly the areas under attack. Another search exposed the perpetrator: physiological leaf scorch. Leaf scorch usually occurs during drought when the leaves lose moisture more quickly than they can take it up from the soil and distribute it to the leaves. How the tree decides which leaves get water and in what order is another mystery, not so easily solved. On some branches there were bunches of scorched leaves in the middle of the branch while the leaves closer to the trunk and at the end of the branch appeared unscathed.
Early summer in 2019 was wet, just like in 2018, so drought was not to blame here. Leaf scorch happens during drought, but it can also happen when roots get too wet and rot, causing nutrient movement difficulties. Or it can happen after a spell of wet weather, followed by hot weather with winds that dry the leaves. Another possibility is a bacterium carried by leafhoppers and spittlebugs called Xylella fastidiosa, which causes bacterial leaf scorch. However, there was no yellow band in between the brown and green leaf tissue, which is characteristic of bacterial leaf scorch.
The cherry beside it was having no such issues. Sometimes you just can’t do anything right. The tree responded to the wet conditions, but couldn’t change its modus operandi quickly enough when the weather reversed.
The black cherry behind the sugar maple with no scorch.
Are you interested in monitoring the health of the trees in your woodlot? Here are some resources to help get you started: