Leaves turning yellow/black

Now that the sawfly larvae are gone, I am having a problem with the lower leaves turning yellow and then developing dark spots all along the edges, finally moving to the interior of the leaves and finally falling off. This is happening to some of my other plants as well. Some of the roses and dahlias. What the heck do you think is going on here? Thanks for any help. Karen aka liebran

For the roses, I would say black spot, but I don't know if that affects Hibiscus or not. But that would be my first guess. If it is that, make sure you pick up all the affected leaves that fall off and discard them, otherwise it'll stick around and re-infect the plant. I'm not sure how to treat it on something like a Hibiscus, with roses I just wait until the leaves fall off, then get rid of the bad leaves, and in the spring I spray with antifungal as the new leaves are starting to come in, but once you already have the spots the antifungal doesn't seem to be very effective (at least for me). This is also spread easily by splashing water, so if it turns out this is the problem, be careful when you're watering.

Thanks for the info. It seems like this same "condition" is effecting several other plants as well as some of my trees. My black walnut tree is losing a lot of leaves, all yellow with the black/brown spots. My girlfriend called to say that the same thing is happening with her black walnut tree. But I hat it because not only does it effect the hibiscus leaves, some of the new and some not as new buds are turning yellow and dropping off. Aggghhhh. I am wondering if the trees reinfect the plants?? Karen

Karen, I had that happen not too long ago, too. I had my tropical hibiscus close to a rose bush that was suffering from black spot. I moved the hibiscus and took all the spotted leaves off. Now, it's fine again. Would you happen to have your hibiscus close to any rose bushes?

Thanks. No it isn't close to any rose bushes. But my black walnut tree is losing leaves like crazy (and my girlfriends is, too)--with the same look-yellow with black/brown spots. I got some pics today, I have to download them. The begonia has it as well as some of the weeds. I have no idea what is going on. Karen