I have a 7 year old Australian Tree Fern about 8 feet tall that initially appeared to have survived a rough winter here in North Florida with 13 straight nights of sub 32 degree lows (several nights where in the low 20's). It lost all its fronds and then started to come back nicely this spring. However since early May it's fronds barely complete their unfurling before they start to turn brown. There has been no change in the amount water it receives or humidity this summer from previous ones. Another tree fern 15 feet away seems to be doing well. Are there common diseases a stressed Australian Tree Fern may succumb to? What can be done? Thanks.