Hi Everyone, I'm from New Jersey and like to share what I learned about saving my Broccoli plants from those pests that make hundreds of holes (large & tiny) in the leaves of the plant.
First off, if you only have a dozen or less plants it's actually very easy to avoid pesticides and just hand pick the pests form the plants. I tried both ways and think it's easier to hand pick them.
Here in NJ, the holes start appearing in the first half of June. In the daytime, look on the top side of each leaf and you will likely find little light green worms resting on the center vein of the leaf. These are commonly called cabbage worms or cabbage loopers. They are typically about 1/2 inch to 3/4 inch long and about 1/6 inch in diameter. Those are the large ones you can easly see but actually there are more but they are much smaller than that!
After you found a few of the big ones and know what to look for, focus your attention on each leaf and look hard because the smaller ones blend in well. Look all over each leaf on the top and bottom side and you will find very tiny green worrms as small as 1/8" long and only about 1/32 inch diameter. They like to hide right next to the tiny veins on the underside of the leaves and it's easy to miss them unless you know what to look for. If you are a newbie, I recommend using a magnifying glass just until you know what they look like..
Once you find the worms, you can simply squish them betwen your finger tips. For the very tiny ones, it's just easier to quish them right onto the leaf than to try to pick them up.
Anyway, I found that you only have to pick them off for a few weeks early in the season and then they seem to disappear completely for the rest of the season. I'm not sure if that is unique to my location so someone else might want to comment on this.
BTW: The reason I posted this long detailed tip is becasue this topic comes up each year in this NG and even though I read the posts it took me several seasons to find out that there were also the very tiny ones hiding on the undersides of the leaves. I hope this helps you too!
---pete---