Maple Tar Spot infected leaf. Image used with these permissions: Use:Saforrest, Black tar spot on sugar maple, CC BY-SA 3.0
I’ve received a lot of questions about the diseased Maple leaves falling early and whether they’re safe to compost.
I’m terrible at this whole “don’t give an answer right away in order to drag readers along” so here’s the short answer:
If you hot compost, you can compost them.
If not, send the leaves away.
More explanation and information after the jump.
First of all, we’re dealing with two diseases on the Maples this year. These diseases have been with us forever and will be here next year also, regardless what you do.
- Maple Tar Spot, which is largely an aesthetic issue that causes the leaves to get large black spots on them. I see this every year though to a much lesser extent, and I’m kind of surprised at how many people haven’t noticed this before.
- Maple Anthracnose, which is a completely separate problem and is aiding in the early leaf drop.
The fallen Maple leaves contain spores from both diseases. Left alone, the spores will survive the winter and in the wet spring they will grow and spread to the trees.
If your compost gets hot (140° or higher for an extended period) and you are confident you’ll get all of the leaves to decompose in that high heat, then you can compost the leaves. The reality is that most home composters do NOT reach that level of heat or thorough decomposition of all materials. That isn’t a bad thing – we’ve all got other things to do with our time.
If you’re among the 99.8% who do not hot compost in a thorough manner, you should rake what you can and send infected leaves away in the municipal yard waste. It is a good idea to get rid of the leaves you can but don’t freak out over this as it is mostly an aesthetic thing when it occurs in such abundance like it has this year.
Getting rid of the leaves will help remove many of the spores from your yard but realistically, your yard is going to be covered anyway unless you use a vacuum cleaner on your yard and every other yard in a 200 mile radius. Still, reducing the number of spores (by getting the leaves off site) is probably a good idea.
EDIT: A Cornell professor says that composting the leaves is just fine, as long as you’re not composting directly under a tree that might suffer from Tar spot. I’ve asked for further clarification and will update here or with a new post once I learn more.
EDIT 2: See update, with more from Professor Hudler.
If you “hot compost” like I and the municipal compost facility do, it is less of an issue. There will be more leaves later in the fall and you can always use newspaper.
Finally, next year some number of these Maple trees will die. Some will blame it on one or both these diseases, and they may even be correct, but only partially. Neither of these diseases, even in combination, are likely to kill a healthy tree. If a tree dies because of this year’s infections, it is almost certainly because the tree had other significant preexisting conditions. Please keep that in mind.