Thanks for the responses. These worms ate through the stem only...didn't touch the leaves. Last night when i got home i picked a bunch of teeny-tiny caterpillar-looking things off the leaves of one other broccoli plant (not sure if they were the same type of thing that ate through the stem, though), then sprayed them all with a garlic/soap/pepper mixture. There was no more damage when I checked this morning, so I watered them well and covered with some row cover. We do have a lot of white moths (my garden is in a wooded area by the house), so maybe they're the problem.

Sawfly larvae most likely. They will turn into an ugly tan and black, wasp looking flying pest and nuisance. Pick the bugs off and squash them gleefully. If you look closely further down the cane of the rose, you will likely see a black section and lesion. This is where the larvae hatched from. The adult sawfly lay's eggs right into the tender new rose canes and these worms hatch from there and eat all the tender new growth and buds. They are a nuisance here at this time of year.

I use plain ole Sevin dust on the leaf rollers which attack my canna lilies. Applied early as they begin growing, it seems to insure they grow all season long without further leaf roller problems. This year, I was preoccupied with hosta anf forgot the lovely Phasion and Tropicana cannas, until now they are basically a mess. However, new leaves are emerging without blemish. A dusting of Sevin did the trick there. But it can also leave permanent signs on the hosta leaves, if you sprinkle it on them. I tried that on a couple of hosta when the sawfly larvae were messing with them, and quickly stopped. Now I use the Bayer spray with Magic in it to control those tiny worms, and reapply it whenever I see a fly hovering around a plant.

i second BT...Bacillus thuringiensis go to your garden center and get a bottle of "caterpillar killer." that's BT...it's a bacteria that acts on the digestive system of the caterpillars and kills them...but is totally safe to us. it's organic...and you have to spray every seven days or so...but (for me) it beats having to hand pick if there is a heavy infestation. although...if they are only eating leaves and they are just an annoyance more than anything...then i would just hand pick. admittedly...i hate touching squishy caterpillars...(heebie jeebies) ESPECIALLY horn worms!!!! they're SO huge...they seem almost...animal.