Hello, We live in north eastern WI.  We have approximately 100 feet of everbearing raspberries.  Each cane lasts two seasons -- in year one it gives berries in the fall Sept-October time and the following year it bears fruit in end of July-August before dying off.  This is the first year we have noticed what appears to be raspberry cane borer...or something very similar.  We have not seen the insects themselves, but are finding rings around the tops of some plants and are having tips break off at that ring level.  Much of the advice I have read online recommends trimming off the canes approx. 6 inches below the bottom-most ring in hopes of trimming off where the larvae are before they travel farther down the cane and overwinter in the bottoms.

 My question:  It's the beginning of August and the tops that have not yet broken off are loaded with raspberries that will come ripe in the next 4-8 weeks..  How quickly do the larvae move down?  And how far?  Do I need to trim off the top now?  I will lose a significant amount of berries doing this.  Or can I wait until I get this fall season's fruit off and then take out the whole plant?  Will that be soon enough?
 
Thanks.