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Last year I used row covers on PVC frames to effectively keep cabbage worms off my broccoli and cabbage. I put the covers on in spring as soon as I put the seedlings in the ground, and then took them off when the plants were larger. There were some worms in the broccoli when I harvested, but they don't do much damage and come out of the heads with a good soaking when brought inside.

This year I didn't put the covers on early like I should have, and I'm wondering: is worth my time to put covers over more mature plants that already have cabbage worms? Will I just be "locking the bad bugs in"? What if I first spray with Bt, which seems to have been effective at controlling them so far, and then cover?

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up vote 4 down vote accepted

I would personally use BT, and then use row covers.

I will note that I have not yet grown anything in that family yet, but from what I found online, these critters have 3-5 overlapping generations (I had a suspicion that this was going to be the case). So BT should kill off the current larva, and covering should prevent additional ones.

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Wood ashes sprinkled over the plants causes present worms to shrivel and die and prevents future worms. It also is high in phosphorous and can be used in place of lime.

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Thanks for the tip. I'll have to hold some in reserve this winter. –  bstpierre Jul 6 '11 at 2:52
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