Dead Space 3

Weedkiller - 30G

This one is easily skipped over, and is fairly easy. In Chapter 14, right after you get the research lab key card, you will see a group of Cysts as soon as you open the door. This is the ONLY time you can get this!
First, what you are going to do is stasis the first two cysts. Then, you are going to run past them, but watch out, you want these guys to live! For now... So pull their pods that they launch away from them (the pods will also be slowed because of stasis) and launch them at the ceiling or something, as long as it doesn't kill them. Then, turn around and stasis the third one, run past him and safely rid of his (her?) pod as well. As soon as that is done, continue on and do the same for the 4th. Once that is taken care of, you are in the clear. When you get to the end of the hallway, your 5th cyst will be on the wall around the corner (next to the lockers) simply stasis him and run by, no need to take care of his pod. Once this is done, simply continue with the main objective, and soon you will be directed to cleanse the room with the gas. Easy as that!
Also, if at anytime one of those cysts dies prematurely, do not be afraid to restart from checkpoint, as there is a checkpoint literally before you open that door! Have fun!

hey i know some people like videos so i found a link seems really easy. just going to point out that doing this achievement solo is easier than co-op.

Weedkiller (Secret)
Kill 5 Cysts in the Biology Building with a single poison gas cloud.

The oppurtunity for this achievement will come during Chapter 14. Once you gain key access, you can follow the mission indicator to the "Biology" sector. Once opening the door, you will see small plants along the ground and walls. You will have to make it through this room, without any of them dying. To do this, just walk near them and use statis, then when the spore comes out, grab it using TK. Now aim somewhere safe and shoot the spore to blow it up. Do this for all 5 cysts. Now, at the end of the room, you'll notice that the gas is stuck, so go down the lift, restore power, then come back up and deploy the gas, killing the 5 cysts, gaining the achievement.

Here is my guide from my channel, Toslow Gaming. On chapter 14, you'll given the key to open any door. Go to the Biology lab and you'll find 5 Cysts. Stasis each one before they shoot a bomb and kill themselves. Kinesis the bomb and destroy it from a safe distance from the shooting Cyst. You''l need to do this process 5 times and turn on the pump. Go back up the elevator and start up the chemicals! Make sure you put HD.

On chapter 14 when you encounter the cysts you can go past them all without killing them but you need to take it slow and at a sensible pace.

When you go near them and they throw their mine into the air it will typically bounce to the floor killing themselves in the process. To avoid this stasis them when you have alerted one and catch their mine in the air using your TK. Dispose of them against a higher wall or the ceiling etc to ensure you do not kill any other cysts in the corridor.

Can be done in coop here is video going from where you first encounter them up to where the achievement pops. Good luck.