HELP! Asters turning brown!
I have a long row of purple dome asters along the top of a native stone wall. Last year it was absolutely beautiful! Lately I have noticed that the stems underneath and bottom leaves were all turning brown but there were still lots of green bushy leaves at the top of the plant with buds forming. Now the tops of some of the plants are turning brown too! It started at the south end of the row and is creeping north and most of the plants are affected. I have been noticing webs now and then among the leaves but didn't think much about it---just knocked them off as I watered. Could it be something called spider mites or some other garden pest? Or maybe they got a whiff of weed killer? Other plants near by don't seem to be affected---yet anyways. Hmmmmm???? What do you think it is? What should I do? I hope someone has some advice for me. Thank you for any help you can give me.