My esteemed BIL wrote on his blog (link on the side) as follows:
>>>There's a machlokes in Yerushalmi Kilayim between R' Yochanan and Reish Lakish as to when the zeri'ah of kilayim is considered to have been done - according to R' Yochanan it is only when the zera'im hit the ground; while according to R"L it is once you release it from your hand:תלמוד ירושלמי מסכת כלאים דף ה/אזרע שני מינין בבקעה שני מינין בחורבה שני מינין וחלקן גדר. ר' יוחנן אמר פטור. ר"ש בן לקיש אמר חייב. מודה ר"ש בןלקיש בזורע ע"ג הים ע"ג פטרה ע"ג סלעים ע"ג טרשים שהוא פטור. מודה ר"ש בן לקיש בזורע ע"מ לחלקן גדר שהוא פטורBut we find in the Bavli the famous machlokes R"Y and R"L on aish:תלמוד בבלי מסכת בבא קמא דף כב/אאתמר רבי יוחנן אמר אשו משום חציו וריש לקיש אמר אשו משום ממונו וריש לקיש מאי טעמא לא אמר כרבי יוחנן אמר לך חציו מכחו קאזלי האי לא מכחו קאזיל ורבי יוחנן מאי טעמא לא אמר כריש לקיש אמר לך ממונא אית ביה ממשא הא לית ביה ממשאIsn't this a contradiction?Isn't R"L in Kilayim more in sync with chitzav?Any suggestions?Let's see if my BIL has something to say.<<<
Let me just note that the Ridba"z starts his very lengthy comments to Kilayim 5 "Hasugya hazos hachamura...", which is never a good sign. Warning: I am going to tackle this halfway, the rest you will have to look up : ) Reading Ridba"z, Reish Lakish seems to hold by Kilayim that the oseir is the akira, even without a hanacha. The way I understand that is through the principle (Kesubos 31) that "akira tzorech hanacha hi" - since the akira leads to a hanachas issur, the chiyuv starts from the moment of akira. The gemara writes that if I shoot an arrow on Shabbos and it rips clothes in the way, I am patur on the clothes because "akira tzorech hanacha", the shooting of the arrow already had the potential for the chiyuv misa of Shabbos and kam leih b'derrabah minah, you cannot be chayav misa and mamon in one act.
When it comes to "isho m'shum chitzav" or "m'shum ma'mono", at first glance the debate seems to center on this very principle of whether you say "akira tzorech hanacha" or not. However, if you look at the case in B"K 22, an eved is chained to a haystack and burning the eved creates a situation of kam leih b'derrabah mineh so you are patur on the haystack. The Rashba asks why this should be so: the eved inevitably dies first before the burning of the property (the haystack)? Conspicuously absent from the Rashba is the teirtuz I would have given: Akira tzorech hanacha, i.e. once the fire is lit, the potential it has to consume both the eved and the haystack causes the chiyuv immediatly. QED that the machlokes R"Y and Reish Lakish in B"K has nothing to do with this principle (and is therefore also unrelated to the issue in Kilayim)!
Now comes the hard question: why indeed are the 2 sugyos not related, and why does the Rashba not use the teirutz of "akira tzorech hanacha"? I don't know if I can do justice to explaining this, so if you are interested, ayen Birchas Shmuel B"K #17:5. In a nutshell, "akira' tzorech hanacha" is invoked to define what constitutes an "action" - shooting an arrow is the same as physically walking along and ripping everything in the arrow's path. If I want to know what the act of planting kilayim constitutes, this issue comes into play. When you start talking about nezikin, it is entirely possible to be chayav even when no overy action occurs, provided you are a cause of the damage that transpires.
Intellectual honesty causes me to just note that there is an answer of "akira tzorech hanacha" given by some, so the kashe would need some more work.