How do I use by spray to kill cabbage worms?

[Purrfluff]

I was hoping I would avoid the imported cabbage worm in my fall garden but no such luck. I looked at some broccoli leaves and I found the orange dots and under the leaf was a green caterpillar munching away.

I kind of prepared for this by getting some Thuricide bt spray (I could only find the liquid and not the dry concentrate). I mixed it up in a sprayer and started spraying everything.

But I'm not sure I'm doing it right. For one thing I found it very hard to get the spray on the underside of the leaves, especially where the plants have gotten a little thick (like the mustard and collards). I suspect I was not able to completely coat all the leaves.

Does this matter? Will the BT sort of "migrate" to the underside of the leaves or into the plant if I spray the tops of leaves?

Also, does watering or rain just wash the BT away? There is an extended period of rain forecast for next week. I'm concerned that the BT will simply wash off and on those rainy days the worms will just annihilate my brassicas.

Will regular watering via a watering can or a hose nozzle blow away all the BT?

It's important that I get these worms under control because 90% of what I planted is in the cabbage family and I planted a lot.

I'd prefer to just use something mild like BT but I will use the nastier insecticides like pyrethrin or rotenone if I absolutely have to.

Thanks for reading the long post.

 

[Chuck]

Bt kills by ingestion. If the caterpillars are on the underside of the leaves you must place the Bt where they are in order for them to ingest it. It is sometimes difficult to spray the underside of leaves. I put aside my pump up sprayer and use a spray bottle instead as I have found this to be a little easier. Bt is destroyed by sunlight. It's effectiveness is only about 5 days. After Bt has dried on the leaves sunlight is more damaging than rain. 5 days is a long time when a caterpillar is dead within 6 hours of eating it. The effectiveness of Rotenone and the pyrethroids are much less than Bt which is why they are not used much anymore.

 

[Purrfluff]

Thanks for replying. I suppose since they are primarily on the undersides of leaves the sunlight might not destroy the BT as quickly. It's going to turn quite rainy this weekend. I will probably reapply the BT on monday or tuesday.

I should have gotten on top of this as soon as I saw the white butterflies flitting about but I didn't see any eggs so I held off.

On leaves where I have identified a large number of unhatched eggs is there a way to get rid of the eggs? Soap and water? Insecticidal soap (I have that)?

I think the leaves are too delicate for a high pressure water spray. These are still very young plants.

 

[Chuck]

Thanks for replying. I suppose since they are primarily on the undersides of leaves the sunlight might not destroy the BT as quickly. It's going to turn quite rainy this weekend. I will probably reapply the BT on monday or tuesday.

I should have gotten on top of this as soon as I saw the white butterflies flitting about but I didn't see any eggs so I held off.

On leaves where I have identified a large number of unhatched eggs is there a way to get rid of the eggs? Soap and water? Insecticidal soap (I have that)?

I think the leaves are too delicate for a high pressure water spray. These are still very young plants.

For eggs use neem oil. It will smother them.

 

[Purrfluff]

Thank you. I have some of that and I will try that on the eggs. I should probably apply BT again before the serious rain hits. The moths are all over the place now and they are quickly infesting my plants. The damage they did to my cauliflower is extensive. And the cauliflower seems as if it the most delicate and slow growing of my brassicas.

 

[Purrfluff]

I ended up doing another BT spray today. We are slated for rain all week and I figured I needed to get the BT on there while I still had the chance. I hope it doesn't all wash off tomorrow. I intend to apply another spray of BT once it clears up. I should have started this two weeks ago but I didn't notice damage until recently.

I tried to get more of the spray on the undersides of the leaves but it's easier said than done on many of the plants.

If this doesn't work I guess I will try neem oil. Though I think it's supposed to take a couple of weeks for the BT to really show results.

Any corrections/thoughts would be appreciated.

I'm being a worrywart about this because 90% of what I planted are in the cabbage family and if these bugs wreck my plants my entire fall garden is shot.

 

[Chuck]

Bt once ingested kills within 4 hours. Feeding stops with the first bite. If caterpillars are the only pest then Bt is what you want to use, but, if you have insects also use a spinosad based product.

 

[Purrfluff]

I'm not totally certain that the cabbage worms/moths are the only pest but I think they are the main one. I have holes in the leaves of most of my brassicas but the peas, beans, and dill have been left alone. The carrot tops are so tiny it's difficult to tell if anything has been munching on them. The sage, rosemary, and chives have been in the ground for years and I don't see them getting eaten. I am seeing some damage on the lettuce.

I suspect slugs are a problem too. But it's been very dry this summer which I think kept the slugs at bay. On the other hand this rain will bring them back so I put down Sluggo around most of my veggie rows.

The rain come on today as expected. The upside is that I didn't see the damned cabbage moths flitting around. I'm going to re-spray BT on the next dry day.

If the BT doesn't do the trick do you think I should move to neem oil or spinosad?

I put in a few rows of nasturtiums as a possible trap crop but they aren't growing fast enough to be a substitute for the brassicas.

 

[Chuck]

I'm not totally certain that the cabbage worms/moths are the only pest but I think they are the main one. I have holes in the leaves of most of my brassicas but the peas, beans, and dill have been left alone. The carrot tops are so tiny it's difficult to tell if anything has been munching on them. The sage, rosemary, and chives have been in the ground for years and I don't see them getting eaten. I am seeing some damage on the lettuce.

I suspect slugs are a problem too. But it's been very dry this summer which I think kept the slugs at bay. On the other hand this rain will bring them back so I put down Sluggo around most of my veggie rows.

The rain come on today as expected. The upside is that I didn't see the damned cabbage moths flitting around. I'm going to re-spray BT on the next dry day.

If the BT doesn't do the trick do you think I should move to neem oil or spinosad?

I put in a few rows of nasturtiums as a possible trap crop but they aren't growing fast enough to be a substitute for the brassicas.

If it is caterpillars Bt is the best thing there is. The second best for caterpillars is spinosad. Neem doesn't do much on caterpillars. Neem is good for scale insects and all eggs, although it does a fair job on most insect pests. Without a doubt spinosad is the best all around pesticide although it doesn't kill eggs very well.

 

[Purrfluff]

Thank you for replying.

I peeked out at the garden today for the five minutes it wasn't raining and the cabbage worm damage continues. I found a very alive worm on the underside of a collard leaf where I saw some pretty bad damage. I have a bad feeling the rain washed away all the BT.

If I pull back leaves far enough to look or spray under them I almost always break the stem but I may have to get more forceful when spraying. These worms are devouring everything and the damage appears to be accelerating.

I'll spray BT again on the next dry day. But if this pattern of rain continues (which it usually does in this area) it could just keep washing away everything I put on to control the worms.

Maybe I do need something like spinosad that will do a contact kill. I'm assuming you can't spray both spinosad and BT?

 

[Chuck]

Thank you for replying.

I peeked out at the garden today for the five minutes it wasn't raining and the cabbage worm damage continues. I found a very alive worm on the underside of a collard leaf where I saw some pretty bad damage. I have a bad feeling the rain washed away all the BT.

If I pull back leaves far enough to look or spray under them I almost always break the stem but I may have to get more forceful when spraying. These worms are devouring everything and the damage appears to be accelerating.

I'll spray BT again on the next dry day. But if this pattern of rain continues (which it usually does in this area) it could just keep washing away everything I put on to control the worms.

Maybe I do need something like spinosad that will do a contact kill. I'm assuming you can't spray both spinosad and BT?

Yes, you can. You can even mix them together. Contact kill on caterpillars is difficult without using very harsh chemicals.

 

[Purrfluff]

For a week or so I will stick to the BT because you said that is the best stuff against caterpillars. But I may pick up some spinosad as a backup. I believe Bonide has something called "Captain Jack's Dead Bug Brew" that is spinosad.

I'd prefer not to use very harsh chemicals but I'm not ideological about my gardening. But it makes sense (to me) to start with the least nasty insecticide before breaking out the big guns. I also don't want to kill the local honeybees if I can help it.

I just wish the damned yellow jackets would eat the cabbage worms instead of coming after me.

 

[Purrfluff]

I've been spraying BT pretty relentlessly. There is still cabbage worm damage to leaves but if it stays at this level I can tolerate it.

What's puzzling is that I've BT on every cabbage family plant I have. But I still have plenty of the butterflies hanging around. If I'm killing the caterpillars with BT where are the butterflies coming from? Shouldn't I be interrupting that life cycle?

I have a issue though which is that some kind of critter burrowed under and around some of my crops.

I am guessing it is voles or gophers. I know we have gophers or moles around because in the back pasture there are dozens of dirt mounds/holes that they've created.

This is the first time I've seen them in the garden but I have a lot more root crops than ever before so I assume they are after things like the beets, turnips, rutabagas, and radishes.

Why is every living thing intent on destroying my vegetable garden?

 

[Purrfluff]

I think the BT is keeping down the worst of the damage. I have seen few skeletonized leaves there is still very visible damage to leaves.

From what my mother told me the last time she planted brassicas the cabbage worms utterly annihilated them. She didn't use any kind of control on them. So I am hoping the fact that I still have (mostly) whole plants means the BT is working as intended.

 

[Vishu1708]

I have read that garlic oil is used to control imported cabbageworms..... maybe interplanting garlic might keep them away?