I've had an acer rubrum Red Maple for 3 months in a pot which has been growing vigorously. The growth during spring and early summer has been so vigorous that I've had to trim the tree regularly. Now in late summer I've noticed new leaves are sprouting quickly but they've also quickly curl down and die. They are light green in colour which were in contrast to the usual red which then turn to green. Is it some kind of fungal infestation? Some weeks ago I noticed some fungus on the soil surface which I just pulled and threw away. I then added a very thin layer of new soil on top and I haven't seen the fungus since. The weather has not been hot for a long time here in Sydney, in fact it has rained a lot. I also water the tree daily.
May be bothered by mineral salts in irrigation water there or hot weather. If you've been heading it back repeatedly (not a good idea, as it is likely to result in a twiggy specimen with excessive forking) you may have forced it to make out-of-season secondary shoots which can't take the weather you may be having now. Or, it has picked up a bacterial or fungal infestation that is affecting the recent sprouts. Instead of cutting it back, move it on to a bigger pot or a place in the ground.
Thanks Ron. I think your first explanation may be the answer as if it is a fungal/bacterial infestation, the old leaves would be affected too (although I might be wrong). So far no old leaves has curled down and dropped. I can't move it to a bigger pot or to the ground since I live in an apartment. So from now I'll just let the tree alone and only trim after all the leaves drop in autumn.
