Imported cabbageworm problems

We had our cabbage crop decimated at one of our gardens this year by cabbageworms. Here is the vicious little beast I'm talking about: http://www.vegedge.umn.edu/vegpest/colecrop/cabbworm.htm

Here are my questions:
** Is there any economical way to trap large numbers of this moth before they lay the eggs?
** Where and how do they overwinter? (One site recommends destroying crop residue immediately after harvest to eliminate potential overwintering sites for imported cabbageworms. I've never seen any sign of them on the crop residue though.)
** Is there a way to apply BT so that it will stay on the plant even if it rains?
** Are they in the soil? (We've used floating row covers and they still seem to penetrate the protection...somehow.
** Is mulch a positive or negative for cabbage?

We cannot tend this particular garden more than about every other week. We've tried dusting with flour and salt. Timing is always wrong. I would just quit planting cabbage there, but now they are attacking the radishes, and worse yet, my beloved horseradish plants.

I can only get a limited number of them with my tennis racket! Ideas?

Don't know all the answers Jefe, But I do get very good results with 14 day intervals of BT. I have no solution for rain, but unless it rains immediately after application, the two week interval seems to keep them in check. They are strong flyers, so they can move in from other brassica fields. They do have prefernce among the brassica's so trap plants around the edge of the field may help. I have not tried it, but I have read a couple of articles where collards were planted around Broccoli fields. Probably would not help with cabbage.

A collard trap crop is a good idea. I'm going to try it. We poor northerners can't cook up collards and make them edible anyway. Might as well let the worms eat them.

As far as trap crops go, amaranth did not work at all, however, maybe that only works for cabbage loopers and not the imported cabbageworm.

Rumor has it that they like nasturtiums but I cannot convince them that I would let them eat that if they leave the veggies and brugs alone. Nasty things!! Nothing I have tried works very long or very well. Good luck

Jefe, The concept of trap plants is not to sacrifice them but to lure them to the plant and kill them. Since a collard is essentially a non heading cabbage, I don't if the collard trap will work for cabbage. While I have plenty of the moth of the imported cabbage worm, scheduled application of BT is so effective that I don't have any damage on brassicas. On the other hand, leaf footed bugs will do a number on Okra. Since Okra has to be picked every second day, I can't use an effective insecticide on it. Fortunately leaf footed bugs prefer Jimson Weed. I let it grow around the edge of the field and spray the heck out of it. Bingo, the leaf foots never get to the Okra. If you just let the pest eat away, the population will build up until they overwhelm everything.

Would it work to just torch the collards when the population gets high? Or is it most effective to dust the collards with BT when rain is not predicted?

I would use Bt on the whole field. The liquid formulation holds a little better Than the dust. On the trap crop, I would use the most potent insecticide available for the Cabbage worm. Pyrethrin, Pyrellin, Permethrin, Thirethrin comes to mind. None of these are particularly hazardous to humans but give some alternatives to BT. Note that all of those litlle green worms that survive turn into moths, and each moth lays a lot of eggs which become litlle green worms. The population builds exponentially. They go through 4 generations a year here.

Jefe, it sounds like your gardens have "Clouds" of those moths descending on ya! Zowie!

Most likely, as I'm sure you know, you'd have to zap them when you first see them coming on, and hit the moths with a direct contact spray. I can empathize w/you on not being able to daily monitor your offsite garden, I had that same trouble this yr when I grew an extended garden at a place north of town.

More than likely you'll have to lay your Reemay the very same day you sow your seeds (radish) or set out your plants (brassica, horseradish, etc). A good tilling a couple times b4 planting should unearth the overwintering pupae and expose them to birds.

As for extending the time Bt is working, Gardens Alive makes a sticker product you might want to try. (I've never used it but others say it works great!). 'Tis called "Weather Shield" and Bt is one of the items it can be used with. (Most likely the liquid form of Bt, "Thuricide".)

http://www.gardensalive.com/product.asp?pn=2341

I think I'd be inclined to email Gardens Alive and ask the duration of time the sticker keeps the spray on the plant. Their description only says "an extended period of time" and doesn't give number of days.

As for companion plants/repellant plants, many of my most trusted books recommend aromatics (tansy, rosemary, etc) and also tomato. As for using tomato...you're most likely like many of us and tend to set your brassicas out long before your tomato plants, eh? Keeping that in mind, perhaps you can store some tomato leaves (freeze? puree in water?) over winter and then make a spray to use on your brassicas early in the yr. If the tomato plants repell the moths then surely the smell of them might also work, eh? (By the way, I store jewelweed juice overwinter and it stays completely viable and useful for those who easily get poison ivy so I don't see why the tomato leaf spray wouldn't stay viable as well.)

I've also had great luck using mint sprays as a repellant. Don't give up. (You need your greens!)

Shoe.

You've both given me some good ideas. Now for some more research.

I know I'll have more questions later, but here is one right away: Are they coming from under the row covers, or are we just not getting the edges sealed tightly enough. It seems like they are getting in under the floating row covers.

It always helps to actually put a question mark after a question. Sorry. Let's try again.

Are they coming from under the row covers, or are we just not getting the edges sealed tightly enough?

Don't know Jefe. Most of them fly in from somewhere else so many people have good results with floating row covers. I don't use them on Brassicas so I have no direct experience. Do use floating row covers on early crops like beets but not for worms. If I had to guess , I would say coming in from open spaces at the edges. Unless you are letting garden debris overwinter, they should not be overwintering in the soil.