white lines like little trails are leaf miners - not a big threat

partly chewed leaf can be slugs or cabbage loopers (tiny green caterpillars - Google for pics) so you'll have to explore to determine which as they have different remedies.

Dave

Coffee grounds deter slugs, right? I know I had a horrible time with these huge green worms/caterpillars on my brussels sprouts a couple of years back. But I haven't seen them as of yet.

Do either slugs or cabbage loopers come out at night? I just can't seem to find anything during the day.

Kim

Slugs are out at night. Need a flashlight and a salt shaker to sprinkle them with. Major infestations of slugs call for Slug-B-Gone or Sluggo or one of the slug killers.

huge green worms/caterpillars

Define "huge". Loopers are only about an inch long or less. The only "huge" green bad guy caterpillar is the tomato/tobacco hornworm 4" or so and have a horn but they prefer tomatoes.

Then there is cabbage worm - green and llok like loopers but a bit bigger 1 1/2", not huge.

The standard treatment for all caterpillars is Bt (Bacillus thuringiensis). Lots of discussions here about it. But use with care as it will also kill butterfly caterpillars.

You can Google any of these by name and get all sorts of pics to compare with yours to ID them.

Dave

Put on row covers before the butterflies appear and you won't need to use Bt and you won't have any "worms". Row covers are cheap, reusable, easy to put on and take off, and effective. The con is, as a friend used to say, the garden looks as if it's wrapped in toilet paper.

You probably have these. Don't know if I can eat broccoli after this traumatic experience.

http://georgiahomegarden.blogspot.com/2011/05/2011-garden-broccoli-blues.html

Here is a link that might be useful: My Garden Blog

Oh my goodness. I am not sure I can eat home grown broccoli after seeing the pix in your blog. I can deal with a lot of critters on my food (I just pluck them off) but worms like that turn my stomach. I had tomato fruit worms for the first time last year and ripped out my plants early rather than deal with them.

LOL, I told you it was bad. Yeah broccoli just has too many places for stuff to hide. That was the first time I have grown broccoli too so it was not a good initiation for me.

Here is a link that might be useful: My Blog

I can't grow any Cabbage family plants anymore. The plants look perfectly fine and growing until about around now when it warms up hot. The roots have been destroyed by the caterpillars, and the plants wilt in the heat. You don't see any damage before you easily pull up the dying plant... the roots are destroyed.

Is row covers the only option other than poison, they have to stay on until harvest?

How many years would one have to avoid Brassicas to reduce the problem? Just one year? Or two? I only grow a few plants here and there to try to fit in around hot weather vegetables.

When I could grow Broccoli, I once put a Broccoli head into a bowl of water. Over 20 green caterpillars were hiding in the one Broccoli head. Yuck.