continuing brown spots on leaves of Acer Palmatum Orange Dream

Asked August 6, 2019, 3:45 PM EDT

these brown spots have been appearing for over a year now. I was told they were from heat but the spots come even in the cool weather. I have examined the spots with a loop and can see no insects. I keep removing the spotted leaves but the poor little tree is getting sparse. Any idea what the problem could be? It has been in a pot for 2 years now. I purchased online as a 1 yr. old graft.

Clatsop County Oregon container gardening japanese maples

1 Response

Your Japanese Maple appears to have Phyllosticta Leaf Spot.
The cause is Phyllosticta minustissima, a fungus which has been reported from Oregon and Washington. This fungus causes small, irregularly circular straw to tan color spots caused by spores which land on the leaves. The spores may be rain splashed or transmitted by overhead watering.

To control this fungus, rake and destroy fallen leaves, and avoid overhead watering. In time new leaves will emerge.

You may also spray with a fungicide, in the spring, when leaf buds are opening and twice more at 10 day intervals if the season is wet. Consult your local nursery for the proper chemical and always read the label thoroughly before applying.