https://ag.umass.edu/vegetable/fact-sheets/cross-striped-cabbage-worm

It's a cross striped cabbage worm.

Rodney

Hard to believe that Bt had no effect. Did you apply it regularly? Tops and bottoms of leaves?

Agree with above. Bt would have worked just fine on them assuming it isn't outdated, was stored properly, and applied correctly. And early enough.

Given his size he has been growing and eating for some time and given the amount of damage that plant was badly infested and has been for weeks. When there is nothing left on the plant for them to eat then they won't be ingesting the Bt.

Dave

I used BT several times and it worked great and the green pillars that usually show up. I have hit these guys with Bt at least a 1/2 dozen times. I hit them with sevin more then once a month and it kills them but they are back immediately. I have never seen these before and neither have nearby friends (who also have them).

You don't spray the caterpillars with BT, just the leaves. The caterpillars eat the leaves and are poisoned.

Lab is correct. Bt is not a contact pesticide.....did you not read the labels? One must spray the plant (not the insect) lightly, and sit back and wait for a few days. The caterpillar feeds on the sprayed foliage ingesting the bacterium spores. It might take a couple of days for it to get sick and stop eating, but it will. The infected caterpillars don't shrivel up and die.....they stop feeding and slowly starve to death.

If your product hasn't been mixed or stored properly, it's possible for the bacterium to be inactive.

I sprayed the vegetables\ plants not the pillars. I applied it correctly and it had no affect on these guys but a big affect on old pests (cabbage lopers I think). Night and day difference.

I use row covers exclusively--gardener's best friend. I NEVER have problems with brassicas--and I grow a LOT of them--spring and fall Asian mustards, kale, cabbages, collards, etc.

Strange that the BT had no effect on the cross-striped cabbage worms, yet it killed the other cabbage caterpillars. I checked, and it is a moth, so the BT should have worked - in theory. Row covers sound tempting for next year don't they?

Linda

I think ingestion of Bt stops eating immediately. Takes a few days to kill the caterpillar. Also, it isn't the Bt spores that kill. It is the toxins they produce. Not completely clear to me that Thuricide even has live bacteria. What you're spraying on is the toxin.

That being said, cabbage loopers are known to have developed some resistance to Bt. If they can do it, maybe the cross-striped worms can manage it.

Resistance to Bt is very uncommon in home gardens.

Large-scale commercial operations are are where the possibility of resistance exists.

Bt works ONLY IF the cats are less than half-grown.

Older ones "escape" the effects of Bt and can successfully pupate and transform into the adult moth.