Something is cutting off my 20 year old clematis stems near the growing tips. Diatomaceous earth has not helped. I have not seen this problem ever before. Only one of my multiple clemati is affected. It is trained onto an trellis against the wall of my house. Any thought? Thanks.
Squirrels will sometimes eat tender shoots if their preferred foods are not available especially in the spring, however clematis plants have a toxin that irritates the stomach though it is not usually life threatening. The more likely culprit is earwigs. They like to feed on leaves and tender shoots and hide in cracks and crevices during the day. Your trellis could provide hiding places for them. Try setting some earwig traps to see if this is the case. See the link below for suggestions of how to do this.
https://www.canada.ca/en/health-canada/services/pest-control-tips/earwigs.html