Meaningful girdling (ringing) experiment cannot be performed within sugarcane because :

The meaningful girdling experiment cannot be performed within sugarcane because its vascular bundles are not present in ring. Monocots have scattered vascular bundles, while dicots have a continuous ring arrangement of vascular bundles. In a dicot stem, after a few years of growth, phloem is present as a single continuous layer or sheet on the outer side as a constituent of bark. 
It can be easily removed because it is present as a continuous sheet. In a similar manner phloem cannot be removed in a monocot stem, because of the scattered arrangement, some of the vascular bundles might be present near the surface and some embedded deep inside. 
Removing phloem from each of the bundles individually is not possible. The girdling experiment is used to identify the tissue through which food is conducted. In this experiment, a ring of phloem is removed from the woody plant.