Attack of the Cabbage Root Maggot!

All my lovely Broccoli is gone, one moment they were strong sturdy young seedlings and then all of a sudden they started to wilt. I was suspicious that this was more than just a case of thirsty plants as I had been keeping them watered well. So I pulled one of the plants up and sure enough the root system had been almost totally devoured by these little white worms.
The Cabbage Root Maggot

The Cabbage Root Maggot

I immediately pulled up the whole row of Broccoli,  every one of the plants were infested. Really disgusting! 
 After doing some research on the web I found that the only good way to control these critters organically is with beneficial nematodes.  So I found some fresh nematodes at Garden Fever in Portland and sprayed them on the soil. 
It takes a while for them to eat all the worms and larvae, hopefully I acted soon enough to save my kohlrabi and Kale.