Those Pesky Spots on Maple Trees
Photos
During a recent tour of the Ford House latest outdoor exhibit, Vanishing Acts: Trees Under Threat (open during normal Ford House hours from 9 a.m. to 5 p.m. Admission to the exhibit is included with regular admission), a question was posed to me, “What are the black spots on my trees?” I responded by picking up a silver maple leaf (Acer saccharinum) and said, “Is this the problem?” The leaf had several dime-sized black spots all over it.
The disease is called tar spot, which is a fungus in the genus Rhytisma. This disease is purely cosmetic and doesn’t cause permanent damage to the tree. Occasionally, the disease will cause early defoliation of the tree. Tar spot and other fungi have been ever-present in nature for many years. The right conditions such as a susceptible host and proper weather can infect a tree.
The spots reveal themselves late in the growing season as the tree is preparing for winter. There is no appropriate control measure this late in the season. Tar spot can be controlled with a fungicide, but timing is everything. In my opinion, it’s not worth the money to try to prevent it. If you are concerned with the cosmetic appearance of the leaves, you may mulch the leaves in the fall to disrupt the disease cycle. Keep in mind that this will not eliminate the disease, as there are other sources (i.e. silver maple) throughout our community that can play host to tar spot.
I do not support applying fungicides to control this cosmetic issue. Instead, I encourage you to find the beauty of these spots against the beautiful fall color of the leaves.
Bill IV
1:43 pm on Monday, October 29, 2012
Douglas, thank you for the insight. My Maple has those spots and i was wondering about them. I remember them appearing after the monsoon rains of 2011. Good to know it's no big deal because the tree is huge.
Kathy Abke
8:58 am on Tuesday, October 30, 2012
My ash has the same spots & I was wondering what it was. Thanks!
Haulin T Male
11:18 am on Tuesday, October 30, 2012
May I add, most arborist will tell you, it's from excessive moister, that does not get a good chance to dry out. Last year we had a very wet spring........ the spots showed around June, I to was told don't worry, I went to every nursery and asked, as I looked for some thing diff. in flowers. I asked, to get a flavor of knowledge. My town has maples all over, they ALL had the tar spots.
This year, my one maple got them in Sept. (on the side away from the sun) (?) is that a sign...........it is young and not been thinned out yet?
My other Maple never got them at all, both are newish, 26 and 17 ft tall, still reaching for the sky.
With my gardens, I very seldom throw any leaves to the gutter, in the fall. since my walks in the forest show me, Where are the decades of leaves that fall every yr?
One common thread between the internet and local Arborist, get rid of all "Tar" leaves (don't mulch them) so I now rake and contain, for compost P/U.
In closing, that is one reason why I don't rush over to the local DPW to get free "compost" never know what's in it, since it is SOCCRA wide, and your getting what Back.?
Haulin T Male
11:18 am on Tuesday, October 30, 2012
Tarred leaves, and what else..........