Sheviis, Chapter 2, Mishnah 3. In the previous mishnah we dealt with types of field work that may be done only until Rosh Hashanah, and for which there is no need to add on to Sheviis - that is, the law of tosefes Sheviis does not apply to them. Our mishnah too lists additional types of work that are permitted until Rosh Hashanah.
The types of work permitted until Rosh Hashanah:
"Mesaklin" - removing the stones from the field.
"Mekarsemin" - the act of kirsum: cutting the dry branches off the tree.
"Mezardin" - cutting off moist branches, which are sometimes too numerous and need to be trimmed.
"Mefaslin" - several explanations have been offered for this term: some understand that it refers to removing the pesoles, all those harmful growths that develop on the tree; and some understand that it refers to cutting off ordinary branches so that the trunk of the tree itself will thicken.
All of these are permitted "ad Rosh Hashanah" - until the Rosh Hashanah of Sheviis.
The view of Rabbi Yehoshua:
Rabbi Yehoshua comments on zerud and pisul: "Keshem shezerudah ufisulah shel chamishis - kach shel shishis" - just as the zerud and pisul of the fifth year are done, so too those of the sixth year. Two explanations are given for these words:
According to the Rosh: just as the work of zerud and pisul of the fifth year continues into the sixth year, so too the zerud and pisul of the sixth year continue into Sheviis. It emerges that these activities are permitted not only until Rosh Hashanah, but even during Sheviis itself.
According to the Rambam: on the contrary, Rabbi Yehoshua is restricting. The permission does not extend until Rosh Hashanah, but only until the time when people normally perform these types of work in that year - and that time generally comes before Rosh Hashanah.
The view of Rabbi Shimon:
Rabbi Shimon says: "Kol zeman she'ani rashai ba'avodas ha'ilan, rashai ani b'fisulo" - as long as I am permitted to work the tree, I am permitted to prune it. One may prune the tree not until Sheviis and not until Rosh Hashanah, but only until the time when working and plowing around the tree is permitted. And as we mentioned earlier in the tractate, for an ordinary tree one may plow only until Shavuos. It emerges that Rabbi Shimon restricts the permission considerably: not until Rosh Hashanah, but until Shavuos.
In summary: our mishnah lists additional types of work that are permitted until Rosh Hashanah - clearing stones, kirsum, zerud and pisul; Rabbi Yehoshua's words are understood in two ways, by the Rosh, who extends the permission even into Sheviis itself, and by the Rambam, who restricts it to the time when people normally perform those types of work; and Rabbi Shimon restricts pisul to the time when working the tree is permitted - until Shavuos.