Just like the laws of Shabbat have Avot (primary activities that are forbidden) and Toladot (secondary activities – see Massekhet), similarly the laws of shemitta have both Avot and Toladot. The Avot are the agricultural activities that are specifically listed in the Torah (see 25:4-5) as being forbidden during the Sabbatical year, primarily activities of planting, pruning and harvesting.
The baraita that is quoted by our Gemara lists various activities that are considered Toladot, but the conclusion is that these Toladot are only Rabbinic in nature, and are, therefore, not punishable. What is included in the Toladot? Among them we find –
The accepted definition of kirsum is the removal of dry branches, which Rashi points out is identical to zemira (pruning), although zemira is specific to grape vines. Another suggestion is that it refers to the removal of excess branches by methods other than pruning.
Rabbi Yehiel of Paris’ student suggests that this is the removal of branches from a tree so that the tree will grow thicker; the anonymous peirush (commentary) on Moed Katan says that it is the removal of extra roots.
Rashi explains this to mean supporting weak branches of the tree (from the word pisga – height – that is, to lift up); the Ran suggests that it is tying up the branches to help the tree grow; the Meiri teaches that it is the removal of branches.
Rashi understands that this means removing stones that are weighing down the roots of a tree; the Meiri suggests that it is the removal of excess leaves.
Smoking the trees (fumigation) was done with either regular smoke or sulfur smoke, and its purpose is the same as current practice – as a pesticide that kills the insects and other destructive elements on the leaves and the fruit.