Eradicating Cabbage Loopers

This is the first year I've tried broccoli and it's been challenging. 3/4 of my seedlings died, leaving me feeling a little despondent. Then, thanks to a few lightning-charged rain storms, the remaining three perked up and were on the fast track to healthy production.

Flower head developing below:

Unfortunately, 24 hours later, my sweet broccoli floret would look like this:

I found at least twenty tiny, bright green worms and scores more eggs. As far as I can tell, based on the lack of markings of the immature caterpillars is that they are cabbage loopers. See sample below:

Biological controls include companion planting with rosemary, dill and sage, although I suspect it might be too late to use the aromatic herbs to repel existing caterpillars. An Integrated Pest Management (IPM) technique is spraying the entire plant with Bacillus thuringiensis (BT) which would kill young caterpillars. (I've had some measure of success with BT on tomato hornworms, but the key is spraying young caterpillars. The older ones tend to build up a resistance.) And of course there is hand picking them -- if you can spot them.

Even though pictures of the damaged broccoli plant may suggest otherwise, I've caught these intruders at a very early stage. My window of opportunity to begin vigorously spraying with BT is still wide open. Too bad the Co-op is not on Sundays. So I'll be handpicking again today and breaking out the spray guns first thing Monday morning. Wish me luck!