Bt breakdown?

I understand that Bacillus thuringiensis (Bt) breaks down naturally, but I'd like to know how. I'm going to be applying Bt powder, and the instructions say to do it roughly weekly, and especially after it rains.
Now, does this mean that Bt powder loses potency when wet, or just that it gets washed off the plant? Hard to imagine the former since you can keep a spray bottle of the stuff dissolved in water. I know that sunlight breaks it down, but does that mean that if cultivated into the soil it stays there for longer, such that it kills grubs that are just hatching there? I've also read that dry spores have a shelf life of several years (implying that wet spores do not).
Yes, I know you want it on the plant, so I know that you want to reapply if it gets washed off. But what if it just drizzles?
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In article
snipped-for-privacy@gmail.com wrote:

First off, it isn't a chemical. It's an organism, a very tiny organism.
If it gets drizzled off, then drizzle on some more. http://en.wikipedia.org/wiki/Bacillus_thuringiensis
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Billy
There are no lobbyists for cover crops and crop rotation. Why?
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First off, I never said it was a chemical. That actually doesn't have anything to do with my questions.
Perhaps I should have phrased it differently. What makes the stuff die? Something must make it die, or else it would be hanging around buried in the soil forever.

And the answer to my question doesn't appear to be there, nor in the half-dozen other websites I looked at.
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In article
snipped-for-privacy@gmail.com wrote:

First off, living things die, diminish, bring down the final curtain, or join the choir invisible, they don't break down.
Bacillus thuringiensis disappears from plant surfaces rather quickly however they are moderately persistent (whatever that means) in soil (their natural habitat). They are fried by ultraviolet light. http://cecalaveras.ucdavis.edu/bt.htm
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Billy
There are no lobbyists for cover crops and crop rotation. Why?
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In article <wildbilly-23D652.19164610032009@c-61-68-245-

A very clear article.
Thanks
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get the powder to stick to the bottom of the leaves... if you can manage to get it there.

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I hear that if you get it to stick to the bottom of the leaves, it'll last longer because the sun can't get to it. But for squash, you really want it on the stems.

Yes, that has a few insights about persistence.
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Interesting. Thanks.
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snipped-for-privacy@gmail.com wrote:

The problem is it washes off fairly easily and as it is not absorbed by the plant this means it is not available for the grubs to ingest. This is inconvenient but also one of the reasons why it is so safe, it works by the bacteria attacking the gut lining of grubs and they must eat it it for this to happen. But this means it doesn't effect anything else. So no it doesn't effect anything in the soil.
The instructions to apply it regularly are intended to give full coverage and of course to sell more BT. If you can deal with the odd hole in your cabbage it is fine to just apply it when grubs or caterpillars are evident. You don't need it at all when the season is too cold for the insects to be actively breeding and laying eggs on your leafy veges.
David
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OK, but I'm told that borers can live in the soil, and emerge the following season. That's why floating row covers are not necessarily a good idea for borer control. But following the logic here, if Bt washes off the plant and gets into the soil, wherein it is tilled in to make sure sunlight doesn't hit it, why doesn't it just kill those emerging borers? I can only imagine that it's because it doesn't last a long time in the soil. Why? It lasts a long time dry, and it lasts a long time dissolved in water. So why won't it last a long time in dirt? Eventually, I should just be able to take dirt shaded by a plant I've been dusting, and just throw that back on the plants to keep them safe.
This is really a very basic question. What causes Bt to break down (die, diminish, pass away, expire, croak), other than sunlight?
Curious.
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snipped-for-privacy@gmail.com wrote:

Because it isn't a poison as such, it is a microorganism. Grubs and caterpillars need to get it into their gut by eating it for it to be effective, which is why you put it on to leaves and other parts of the plant that makes up their diet, they don't eat dirt.
David
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That makes some sense.
But again, if my soil gets "infected" by Bt with repeated applications, I can stop buying the stuff and just dust the leaves with the infected soil year after year, right?
That is, dryness doesn't kill it. Wetness doesn't kill it. So where does it go, once it's in soil? I guess something else in the soil must kill it. Nothing to live on there? Well, I'd say the same thing when it's dissolved in water, but it seems to do just fine that way. Powder and liquid forms of Bt are active, I am told, for years.
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In article
snipped-for-privacy@gmail.com wrote:

Logic is only as good as its' premise.
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Billy
"For the first time in the history of the world, every human being is
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snipped-for-privacy@gmail.com wrote:

Google "Bacillus Thuringiensis" and persistence; for 35,000 hits
David
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Tried that. That's why I'm here.
(My fingers are pretty sore ...)
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In article
snipped-for-privacy@gmail.com wrote:

Goggle is wonderful..full of wonder but we must know in advance what we are seeking. Good thing or this computer stuff would scare the ........ out of me more so.
look at
<http://extoxnet.orst.edu/pips/bacillus.htm
Key word is half life.
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