Are they little green caterpillars about the same color as the leaves. If so, the white cabbage butterfly laid the eggs on the undersides of the leaves and they hatched out and began eating. If these are the ones you have, you have to keep the butterflies off the plants, or find and destroy the eggs before they hatch.

when I had caterpillars in the Brassicas, I let them be, not for the first time and then I discovered yellowjackets or wasps patroling the Brassica beds and no caterpillars after that.

You can use Bacillus thuringiensis spray nicknamed "BT", it is not a poison but the caterpillars ingest it and makes them ill, very effective.

Bonide Thuricide BT is a brand name you can find at good local garden nurseries. Not sure if you can find dependably at Lowe's or Home Depot.

Amazon Bonide BT

@callirhoe123 there are 2 or 3 different kinds including the pale green ones that are the same colour as the leaves. I did net them last year but it was unsuccessful overall.

This year I am trying to hold them at bay with my sticky fingers and 2.0 magnification glasses.

I am just surprised how quickly they get into the very growing tips of the plant where they do the most damage .

@robert567 Thanks. I will look into that BT spray for next year.

@prairiemoon2 z6b MA my beneficial insects are probably a bit more laidback than yours. Perhaps they have it too easy with all the ivy on the walls and the windfallen apples under the trees.

BT will work very quickly and help solve your problem this year, easier than trying to find them all with a magnifying glass. The caterpillar problem will last until it freezes.

HU - It takes a while for beneficial insect solutions to actually work. If you want something to eat aphids, you have to have a supply of aphids, etc. That is how I ended up with ladybugs that eat the aphids. I had to ignore the aphids for long enough to attract the ladybugs. I've been gardening organically without pesticides etc. for 40+ years, but at first, I was always trying to remove pests myself. It wasn't until I didn't have time and started to ignore the pests, that I saw the beneficials come to the rescue.

As others said BT is amazing. I swear those things show up fully grown in hours. BT is also organic and cheap. Follow instructions. It works GREAT. Handpicking does not even come close to as quick of results and I did it several times a day 7 days a week.

@Donald V Zone 6 north Ohio

Yes I too was surprised how quickly they show up ("fully grown in hours " describes just how it seems to me)

I too have hand picked 2 or 3 times a day for a few weeks .

I think they tailing off now thank god !

By the way, does anyone else scrape the soil just next to the roots and incorporate manure pellets into it during the growing season?

It seems to work for me. I have giant Brussels sprout plant this year after starting this treatment.

Yes, I'll give another shout out to BT, I just sprayed my cabbages for the second and last time of the season, this stuff completely wipes the buggers out and as well is long lasting as it remains viable upon the back side of foliage that is shielded from rain. Now, if the worms have worked their way deeper into the head, such is evident by the holes made and the gross droppings left behind, then just be sure to lift and liberally spray under all foliage that you can!

Just use row covers. Stops the "caterpillars" from the start. I've been using row covers since they first became available--30 years?--and haven't had a problem since.

@laceyvail 6A, WV would you be able to grow broccoli or Brussels under a row cover?