Answer: Based on your description I am not certain what you are seeing. There are many different pests and diseases that could cause wilting of only certain canes. I would suggest you work with your county extension to try to diagnose what is affecting yours. If it is something that requires treatment they will have the most up to date recommendations for Illinois in terms of what can be used and how/when is best to apply it. In the meantime you may find the following information helpful, especially the pages on problems which include fairly detailed descriptions of the symptoms. It was developed for Pennsylvania but the information should be applicable in your area, too. Good luck with your blackberries!
Q&A Library Searching Tips