There might be issues, such as infestation, or in Israel issues like truma and maaser... The shmitta year upon us has brought a new one not considered in most years - supervision on marijuana from the aspect of shmitta. Marijuana grown in Israel during the shmitta year could be a problem of having kedusha, or possibly being completely prohibited if one considers it in the category of sefichin. Other issues might be using hetter mechira for marijuana, or importing from other countries or using what is called yevul nochri - non-Jewish grown marijuana, and one might want supervision for any of those issues.

A company in Israel that produces/grows medical marijuana announced that their product has kashrut supervision from Rav Yosef Efrati ensuring that they are shmitta compliant. The company report believes this certification will spur an increase of sales in the religious and Haredi markets.

This is seemingly the first time a marijuana company in Israel has received kashrut certification.

source: Hamechadesh

we are living in interesting times..

I dont know how they grow the marijuana while being shmitta compliant. Maybe in hothouses, hydroponics, and the like. 

I also wonder if marijuana gown [improperly] during shmitta would have the status of sefichin and be prohibited or if it would need to be treated with kedusha, special care for shmitta produce. And, if one had marijuana with kedusha status, could one just bake it into edibles for consumption or could one also smoke it - ie would burning it be considered its normal use and ok or would it be considered destroying shmitta produce which is not allowed?  So many questions!