From Rich Dunbar,
Division of Nature Preserves – Indiana Dept. of Natural Resources
Many people, including at times myself, recommend bagging and removing garlic mustard because the plants can continue to develop even once uprooted. As you know from direct experience, bagging and hauling out garlic mustard can take as much effort as pulling the plants. This can be especially true if you find a patch way back in the woods. We have had success with crushing the plants. This will stop the plants from developing further. My usual technique is to wring them like a wet towel, but other people on our crew have their own style. If we are near a driveway we sometimes throw the plants in the drive and drive over them as we come and go. It works as an alternative to landfilling them.
Below are three pictures. The first is of garlic mustard pulled and left uncrushed in a gravel driveway. You can see the tips of the plants have curled up toward the light. How many viable seeds a plant will produce when just pulled probably depends on a number of factors.
The plants below were crushed and left on the forest floor two days before the picture was taken. The plants are withering and not developing further. The tops are not very visible because I folded the plants in half before crushing them. Often we will wedge the crushed plants in a tree branch to make sure they dry out.
The plants below were crushed about two weeks before the picture was taken. It confirms that the plants did not continue to develop.
Of course there will come a time when the seeds are so well developed that the plants should be removed. We do not know where that point is. We are making our best guess based on how swollen the seeds are within the pods.