Yes you can. Bt can be used right up to day of harvest.

Dave

Bt is quite expensive over here. Is it really worth it for one cabbage? If you only have a single plant could you hand pick any caterpillars or blast with the hose?

Thanks for letting me know that I can spray Bt. Bt is not very expensive here in california.

Purnima

Purnima may need to hand collect the caterpillars AND spray with Bt. If the caterpillars are pretty good sized, they may be at the stage where Bt just isn't particularly useful. There may be some very young ones as well as the older. Bt will control the little guys.

Of course, this is assuming that it is caterpillars chewing the holes and not something else...like beetles.

I dont see any caterpillars. There are small light brown things over the bottom part of the leaves. I had hosed down with water about a month ago when I first noticed these brown things and saw that the new leaves were just trying to form head. But the brown things came back and I feel may be they were eggs or something. But I dont see any caterpillars. I am anyway going to spray Bt on the leaves.
Thanks,
Purnima

Bt only works on caterpillars - they have to eat it for it to work. So you need to ID exactly what the pest is rather than just waste pesticides.

Dave

I also have cabbage with lot of holes. It was slugs who are making the holes and they are brown and different sizes.

BT is a dead bacteria in suspension. Super safe to use for
the homeowner. It is a gut poison on all lepidopteris larvae (caterpillars). This stuff works GREAT on controlling cabbage worms on cabbage, broccoli, cauliflower,
brussels sprouts ect.

IF I am growing a lot of these types of plants, I spray the
Bt in a pump sprayer. Because of the high pressure and lack of hairs on the plant leaves, it is best to add a few
drops of dormant oil to the mix as a spreader-sticker so it
adheres to the leaf.

For those with just a few plants, mix it in a small mister
bottle and skip the oil. The mister bottle puts out such fine droplets that the spray will not run off the leaves unless you over-apply.