Hello, I live in Alberta and my tree (Japanese maple?) has these yellowish 1mm growths on its leaves. These growths started about two months ago and slowly increasing in number. Does anyone know what this tree is suffering from? Thank You in advance.
Welcome to the forums. Wonder if it could be tar spot, a Rhytisma species. Not so sure it's a Japanese maple, though. http://plantclinic.cornell.edu/factsheets/tarspotofmaple.pdf
When I was in Nova Scotia a few years ago, I found a (sycamore?) tree with leaves covered in yellow-ringed black spots. I was horrified, never having seen anything like that before and had no idea what was the cause. Now my mystery may be explained because the photos sent by Autumnandme are very similar and I wouldn't be surprised if the cause was tarspot, as Chimera suggests. Rhytisma acerinum is a plant pathogen that commonly affects sycamores and maples in late summer and autumn - so seeing these spots this early in the season may indicate it is a different species of Rhytisma on a different kind of tree than in the photos sent by Autumnandme.
Just noticed that underneath the leaves each yellow spot has a "furry" growth. I'm unsure about the Rhytisma theory anymore.
It looks more like some kind of gall in the last photo. It doesn't really look like a maple to me. Is there a retail nursery or Dept. of Agriculture site near you where you could take some leaves so that it and the tree species could be properly identified ?
Definitely not a maple, almost certainly a gall. Unfortunately, we need to identify the tree/shrub first, then it makes finding what might have caused the gall relatively easy.
