Probably old age - raspberry canes deteriorate their second year and are cut out.

Also you will get much better results planting your raspberries in the ground, where they have room to develop fully, than keeping them in pots.

If you are limited to growing them in pots maybe try the new dwarf kinds that have been in garden centers recently instead of trying to keep traditional full-sized cultivars confined to containers that are too small for them.

This happens on the my 1st year canes as the cane in the picture grew this year and it happened on my Dorman Red which is in the ground, starts off good in the spring starts to look bad in summer and now is starting to grow again, could it be the Georgia summer heat or maybe because there in part shade, the one in the pot I water about 3 times a week and the ones in the ground about 1 good watering a week. I did fertilize them back in July which someone told me that might be it?

If you see a cane or two dying back on a raspberry, you shouldn't be too concerned. Raspberry canes are biannual. The real issue is whether the cane was doing well enough before so that the roots have the energy to send up another cane when they are ready. In some cases they don't, and a raspberry plant continues to decline, sending up smaller and more feeble canes as time progresses until finally the plant dies. Don't judge a raspberry by the death of visible canes, but rather by how well the canes were doing before. If, however, 6 months go by without any sign of leafage, the plant most likely did not survive.

my heritages have been in the ground for 5 yrs. and never seen this. maybe its the hot summers? my canes are usually 8ft tall and very green by mid summer! almost too vigorous ! only give them cow manure and mulch with hardwood chips 4in. deep every spring .

i also cut my canes to the ground in early spring for one fall primocane crop on the current years canes.