Cutworms aren't worms. How's that for a start? If they aren't worms, then what are they? They are caterpillars.
So what's that name all about? No problem for me to figure that one out. These caterpillars hide in the top inch of soil during the day, then come out at night to feed. They eat whatever parts of the plant they encounter, which happens to be the stem, usually of a tender seedling. As they munch, they cut the stem right off at the ground. Thus CUTworm.
The bugger about this pest is that they are so incredibly wasteful. It pisses me off to see that they eat only a small section of stem before moving on. I've had them munch down a two foot row of seedlings in one night. I'll come out in the morning to find the little plants lying wilted on their sides. A total loss.
All cutworms aren't necessarily the same species. There are a number of moths whose caterpillars exhibit cutworm behavior. I don't know which moths are responsible for the cutworms I find here in Hawaii, but that doesn't really matter. Attacking all moths just to eliminate cutworm damage seems to me to be a bit irresponsible considering that there are plenty of animals that rely upon moths as food. I don't wish to jeopardize those animals, thus I choose to take steps to reduce cutworm populations in a way that won't effect all moths.
So what do my cut worms look like? They are chubby caterpillars about 1" long. Grey/brown in color. When disturbed they curl up in a ring.
I can find them by stirring up the top inch or two of soil. When I find cutworm damage, I'll go looking for the critter. It's almost usually just one, so it's not like there are dozens around any particular garden spot. Once I find the offender, I'll just simply squish it, adding it to the soil.
I've had other gardeners tell me that they used moistened, sweetened bran mash (a horse feed) that they added BT to. This is then sprinkled on the ground around newly transplanted seedlings that they wish to protect. I've never tried this, but I suppose it might work, assuming the cutworms will dine on the mash.
Another strategy for protecting seedlings is to put protective collars around the seedlings. I've done that and still resort to this when cutworms are bad. Once open a time I used discarded computer punch cards. They were perfect. Stiff enough to hold up, didn't disintegrate in the rain, easily stapled into position, no need to remove, and they were free. I've seen people now use stiff paper or cut up cereal boxes , plastic cups with bottom cut off, and metal cans with both ends cut off. I would think that aluminum foil crinkled around the stem should work too, though I haven't tried it yet. The idea is to create a barrier so that the cutworms can't reach the stem. Collars work to prevent damage but don't eliminate the worm itself.