I have a raspberry patch in my backyard. I cleared dead canes in the fall last year and again this year in the early spring. We mulched the patch in April to keep the weeds under control. The second-year canes and many new 1st-year canes came in green and very healthy (the whole patch looked great), and the second-year canes started flowering. But then about week ago, the leaves on the second-year canes started to turn yellow, and many of these canes are now dying completely. The first-year canes look fine so far. This happened last year too, but I ended up losing a whole large section (1st- and 2nd-year canes) of my raspberry patch while the remaining section flourished. I would like to know what might be causing this and how I might prevent it. Thanks for any help you can provide.