Your thoughts on Bt...is it safe?

pippimac(New Zealand)March 15, 2010

A friend of mine is having a major battle with white butterflies. She was about to haul out the Derris Dust when I went on the "rotenone...bad...off approved organic lists..." spiel and recommended she try Bt instead.

She was very curious about its environmental safety and potential for harming beneficial and indigenous Lepidoptera. I had to admit I had no idea and hoary old truisms like "no free lunch" started playing in my head. I've avoided using it, as I'd rather squash things and not kill off all the parasitic wasp dinner, but I hadn't considered any possible wider implications

She's got a Masters in some sort of biology, so I have to take her concerns seriously.

There's a fair amount of "Bt's bad" stuff online, but I'd be very interested to read your thoughts.

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dan_staley(5b/SS 2b AHS 6-7)

Bt isn't a petrochemical, but can harm non-target species all the same if applied carelessly.

Dan

    Bookmark   March 15, 2010 at 5:44AM
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Kimmsr(4a/5b-MI)

The Bacillus thurigiensis spores will infect only those larva that ingest it, so they must be leaf eating caterpillars if the strain used is Kurstaki. The other strains are similarly somewhat target specific. If you were to spray some on a pipevine or snakeroot when the larva of the Pipevine Swallowtail were there eating they would be killed by the BTK, so due care in application (like any other pest control) is necessary even though the BT's are fairly target specific.

    Bookmark   March 15, 2010 at 6:54AM
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rhizo_1 (North AL) zone 7

Bt products can also harm non-target organisms by being disposed of carelessly (FYI, Kimmsr).

The primary concerns with all of the Bt strains used to control assorted pest insects are pest resistance caused directly by over use, the serious decline in native butterfly and moth populations (and the animals that rely on them and their larvae for food), and allergic reactions.

If each of us would use the products responsibly, there would be less risk to the environment. But Bt products are used extensively in commercial agriculture, agronomy, forestry, etc. I guess I'd rather they spray Bt out of airplanes to control gypsy moths (just for example) than malathion.

Speaking of gypsy moths, science is fast working towards producing microbial and biochemical pesticides that are VERY target specific. Rather than something that is toxic to ANY feeding lepidopterans, we now have a product that is specific to the Gypsy Moth! That's just one example. Cool, huh?

    Bookmark   March 15, 2010 at 12:39PM
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Kimmsr(4a/5b-MI)

The major method of control for the Gypsy Moth has been to aerial spray Bacillus thuringiensis - Kurstaki in affected areas, at a time the Gypsy Moth larva are most susceptible and other insect larva are not yet around. The key is to spray either at a time that others are not affected (before of after they would be susceptible) or use due care (as I stated above) when applying the product.
Researchers have found that there is a natural disease that is appearing in areas infested by the Gypsy Moth that is killing off the larva but they have not isolated that, yet, and do not know how it spreads around.

    Bookmark   March 16, 2010 at 6:51AM
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dan_staley(5b/SS 2b AHS 6-7)

BTW, distractions and tangents notwithstanding, Derris dust is harmful to the environment if applied incorrectly as well. The most important point is life cycle and timing/care of application.

Dan

    Bookmark   March 16, 2010 at 3:30PM
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pippimac(New Zealand)

I think I'll avoid it: having a hand in increasing pest resistance etc is not something I'd like to take responsibility for.
So we really shouldn't use anything that kills anything. Hmm. Surprise surprise.
No more poking brassicas in gaps, they must be segregated under row-covers for their (and my)good.

    Bookmark   March 18, 2010 at 6:47AM
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Michael

pipp: It is possible to use Bt in a manner that doesn't lead to resistance.

    Bookmark   March 18, 2010 at 11:00PM
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dan_staley(5b/SS 2b AHS 6-7)

What michael said. Apply properly and you likely won't induce resistance.

Dan

    Bookmark   March 19, 2010 at 5:02AM
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dchall_san_antonio(8 San Antonio)

I like paper wasps for my caterpillar control. As long as you don't swat at them they are pretty harmless. We remodeled a few years ago and lost all my wasp nests. I'm trying to cultivate a new one outside my back door now.

    Bookmark   March 19, 2010 at 12:42PM
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DDacosta(8b)

With regards to pest resistance to Bt the culprit is shown to be GMO crops that incorporate Bt crystals. Insects feeding on GMO potato and tobacco plants have shown some resistance build up.

Bt when used properly and at the proper timing is very target specific. The spores containing the toxin that actually kills the target insect is only released within the insect if TWO things happen. 1. The Bt is ingested by the insect. 2. The insect stomach is of the correct Ph to dissolve the covering of the crystal. What pest you target determines which strain you use and at time in the insects life cycle you apply it. When used properly and with proper care Bt is very safe to use.

    Bookmark   April 7, 2013 at 10:22AM
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little_minnie(zone 4a)

I use Bt on brassica crops to kill cabbage worms. If I sprayed it on carrots and its relatives I would kill butterfly caterpillars but they are not on the brassicas. See what I am saying? Bt is the absolute safest pesticide because it is so targeted to just what eats it. Nothing else is as safe.

I believe the resistant to Bt resulting from GE crops is in corn rootworms. So cabbage pests shouldn't have resistance yet.

By white butterflies do we mean cabbage moths?

    Bookmark   April 7, 2013 at 7:33PM
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nc_crn

BT resistance in GMO is in a variety of pests...in GMO cotton it's becoming less effective for a variety of pests (especially boll worm) because too many farmers seem to think it's their right to plant a full field of BT rather than the suggested 20/80 non-BT/BT in order to give diversity to the pests. Well, it is their right, but it's a stupid use of their rights. Greed has caught up with some farmers in some areas and now they're having to use more expensive pesticide control measures.

This is huge problem in developing countries (especially India) and the South-East US. In some areas of the South-East US it's currently a 50/50 (n-BT/BT) recommendation for cotton because of farmer misuse. Where they've tried to control it in India the farmers have turned to black/grey-market seed sellers to source their GMO cotton seed because they've been limited from legit sources based on the amount of known cropland they have. Some of that black market seed has caused residual issues...such as not really being GMO seed and farmers not applying correct pest control issues because they assume the plant will take care of it. There's probably as much black/grey market cotton seed sold in India as there is legit seed.

This post was edited by nc-crn on Sun, Apr 7, 13 at 19:49

    Bookmark   April 7, 2013 at 7:46PM
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