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Re: Janet's on Bt

Square Foot Gardening List - http://www.flinet.com/~gallus/sqft.html

Janet Wintermute wrote:
> 
> Square Foot Gardening List - http://www.flinet.com/~gallus/sqft.html
> 
> Janet said, There are a few irregularities in Christy's post to Cyn on the subject of
> Bacillus thuringiensis (Bt).
> 
> Christy said,
>   BT (Bacillus thuringiensis) is a microbial insecticide that is marketed as
> >Dipel, Thuricide and Attack.
> 
>Janet said, So far, so good.
> 
> But there are some inaccuracies in this paragraph:
> 
> >It is a virus that when ingested by the worms
> >kills them. It is approved for organic gardening (food crop) use in
> >California. It breaks down quickly and is only effective for a few days, so
> >you may need to properly time (look for eggs) your application, or spray more
> >than once to get those in the process of hatching.
> 
> Bt is a bacterium, not a virus.  

The name alone should keep me from making that mistake, but I have this
unconscious urge to think of a virus when I speak of this stuff. Second time
I've done it, thank you for the correction.


Janet said, It forms crystalline spores that are
> shaped like elongated diamonds, with points.  These points are what causes
> the insect gut to liquefy.  It's a mechanical thang.
> 
> Bt occurs naturally in some parts of the country; thus it's not quite right
> to stipulate that it "breaks down quickly."  Some of it is there all the
> time. 

I was obviously, not referring to existing Bt, but that which is applierd by
the gardener. I suppose the term "quickly" is relative and left the statement
debatable for anyone who wanted to. I was referring to the fact that Bt breaks
down and loses its effectiveness (in 24-48 hrs) much faster than more toxic
insecticides. 


Janet said, Just not enough to handle society's insecticidal needs all by itself.
> 
> One of the reasons Bt, though much safer than contact insecticides, is
> tough to use properly is that timing is of the essence--but not because it
> breaks down. Bt works only if ingested, so it's got to hit leaf structures
> that form part of the target insect's natural diet, and stick to those
> leaves long enough for the target bugs to wander by and chow down.
> 
> If you get a heavy rain within 24 hours of having sprayed Bt, forget about
> it.  You've got to reapply.  This is not such a hassle when you're talking
> about your garden.  

And we are.

Janet said, But state and federal agencies that spray entire
> hardwood forests with Bt from airplanes (which has been very common in the
> U.S. Northeast for the last 15-18 years because of gypsy moth) are in a
> mess if they have to respray because of the cost.

I do not believe the spraying of entire forests are a common concern for the
square foot gardener.
 
Janet said,> 
> It is not appropriate to spray based on having seen eggs hatch, as Christy
> suggested above.  

Yes it is. 

I very much disagree with you on this.  If I see eggs on my cole crops I pick
them off, but if I go out the next day and see worms, it is pretty much
assured that they are cabbage worms and I am going to spray. I have seen young
plants whose leaves are completely eaten over night. Because new worms can be
hatching every few days it is senseless for a backyard gardener to try and
determine at which larval stage which worm is in, where it is feeding and when
that worm is going to get hungry. 

The University of California Department of Agriculture and Natural Resources
recommends spraying as soon as you see worms.

Janet said, 47Most target insects have more than one larval stage, and
> the trick is knowing at which instar the little "worms" do the most eating
> and therefore are likeliest to take up the Bt.  For gypsy moths, for
> instance, it's about instar #4.  Wait a couple more instars (as you might
> have to do, for instance, if it's raining on the days you need to spray)
> and you're out of luck again.  The bugs are still "worms," but they're
> about to pupate in coccoons prior to emerging as adults, and they've
> stopped eating!!!

I do not pretend to know anything of Gypsy moths, I've never found them on my
cabbage or broccoli. But the caterpillars we are discussing here are the
larval stages of moths or butterflies in the order Lepidoptera. After mating
the female lays her eggs on the host plant. After a few days or weeks (or the
whole winter the case of species that spend the winter in the egg stage), the
eggs hatch and larvae (or caterpillars/the worms we were referring to) migrate
to feeding sites on the plant. Caterpillars can eat voraciously and grow
rapidly, shedding their skins (molting) three to five times before entering a
non active pupal stage.
Again: The University of California Department of Agriculture and Natural
Resources recommends spraying as soon as you see worms.

> 
Janet said, > Christy is right about this:
> >  It takes the worms a couple
> >of days to die (their insides liquefy, eeech!) but they usually stop doing
> >damage soon after becoming infected.
> 
> >I especially like not having to go eye to eye with those big tomato worms when
> >I'm picking. I think I read somewhere that BT even kills mosquito larva, but I
> >wouldn't know what to spray it on to kill them?
> 
> Well, I don't know anything about Bt on mosquitoes. 

Your research may not be current.

Originally, Bt was
> billed as solely killing the larval stages of lepidopts (butterflies and
> moths).  In recent years, I have seen posts on the 'Net suggesting that it
> works on some beetles.

This is true....

> 
> If you've got a bag of Bt around the house, check the label. 

ALWAYS CHECK THE LABEL ON ANYTHING YOU ARE SPRAYING! I should have emphasized this.

 The U.S.
> Environmental Protection Agency requires that all pesticide labels clearly
> indicate which pests the product can be used against.  It's a violation of
> federal law to use any insecticide against a pest not specifically OK'd on
> the label.  Even if it works against them!
> 
> Make no mistake:  using Bt against appropriate pests is much less harmful
> to other insects and aquatic invertebrates than using a contact insecticide
> like malathion, chlorpyrifos, or Sevin.  (Bt is also less dangerous to
> mammals, including human pesticide applicators, than the contact
> pesticides.)  But Bt is also tricker to apply correctly and, as Christy
> indicated, you must be prepared to postpone your gratification long enough
> for some vegetation consumption to take place in order for it to work at all.
> 
> --Janet

Thank you for pointing out a very large error on my part regarding Bt being a
bacteria not a virus as I stated. I appreciate your willingness to contribute
and also the diversity of your knowledge. None the less, I can not help but
question the application of some of these facts in the case of cole crops.

Christy


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