First of all why the hell do you want to kill marijuana plants????
Second of all, why the hell are you guys all giving him ideas?
If I were you, to kill it, I would get some good nutes, feed it once every other week with the nutes, and water in between. If your indoors switch the light to 12/12 when the nodes start to alternate, then wait about 8 weeks, maybe more if it needs it, *then cut it, and hang it upside down for a week or two, in a dark spot. After that, I would reccomend curing it for another 2-3 weeks. Place it in a airtight jar, then close the lid. After about 8 hours, open the jar and give it some fresh air, move the weed around with ur fingers. Close the jar again and then wait 12 hours, then repeat the last step. Then I would say about every day repeat this process. After the three weeks, call me : )