I just tear them half way through and slide 'em around the stem.
Attachment 298214Attachment 298215

Stops root aphids, mosquitoes, and yellowjackets too.
Anything that hunts by scent.
It won't kill off an ongoing infestation, but it does slow it down.

Un-infested soil stays clean, and it allows air exchange.
You can water through it, but I lift it up for watering.
No wanna knock down the scent.

Aloha,
Weeze