This entry is a copy from a KNOL I wrote found at Google. Google will be discontinuing the KNOL's platform and I am in the process of storing them on my blog. Please enjoy the article. I have about 50 coming over to this blog.
Leaf eating caterpillars typically attack my cabbages and kales. Bacillus Thuringiensis (Bt) is a way to control caterpillars in your garden. Bt is a bacteria that kills the caterpillars by interrupting their digestive process. The caterpillars starve to death. Bt is documented as having an extremely low toxicity to humans and other forms of life. Simply put... Bt targets the caterpillars.
Controlling Leaf Eating Caterpillars with
Bacillus Thuringiensis (Bt)
Is it Toxic to Humans and Other Wildlife?
- Acute toxicity: B.t. is practically non-toxic to humans and animals. Humans exposed orally to 1000 mg/day of B.t. showed no effects . A wide range of studies have been conducted on test animals, using several routes of exposure. The highest dose tested was 6.7 x 10^11 spores per animal. The results of these tests suggest that the use of B.t. products causes few, if any, negative effects. B.t. was not acutely toxic in tests conducted on birds, dogs, guinea pigs, mice, rats, and humans. No oral toxicity was found in rats, or mice fed protein crystals from B.t. var. israelensis . The LD50 is greater than 5000 mg/kg for the B.t. product Javelin in rats and greater than 13,000 mg/kg in rats exposed to the product Thuricide [147,148]. Single oral dosages of up to 10,000 mg/kg did not produce toxicity in mice, rats, or dogs . The dermal LD50 for a formulated B.t. product in rabbits is 6280 mg/kg. A single dermal application of 7200 mg/kg of B.t. was not toxic to rabbits . B.t. is an eye irritant; 100 grams of formulated product applied in each eye of test rabbits caused continuous congestion of the iris as well as redness and swelling . Very slight irritation from inhalation was observed in test animals. This may have been caused by the physical rather than the biological properties of the B.t. formulation tested . Mice survived 1 or more 1-hour periods of breathing mist that contained as many as 6.0 x 10^10 spores B.t. per liter .
- Chronic toxicity: No complaints were made by 8 men after they were exposed for 7 months to fermentation broth, moist bacterial cakes, waste materials, and final powder created during the commercial production of B.t. . Dietary administration of B.t. for 13 weeks to rats at dosages of 8400 mg/kg/day did not produce toxic effects . Some reversible abnormal redness of the skin was observed when 1 mg/kg/day of formulated B.t. product was put on scratched skin for 21 days. No general, systemic poisoning was observed .
- Reproductive effects: There is no indication that B.t. causes reproductive effects .
- Teratogenic effects: There is no evidence indicating that formulated B.t. can cause birth defects in mammals [143,148].
- Mutagenic effects: B. thuringiensis appears to have mutagenic potential in plant tissue. Thus, extensive use of B.t. on food plants might be hazardous to these crops . There is no evidence of mutagenicity in mammalian species.
- Carcinogenic effects: Tumor-producing effects were not seen in 2-year chronic studies during which rats were given dietary doses of 8400 mg/kg/day of B.t. formulation . It is unlikely that B.t. is carcinogenic.
- Organ toxicity: There is no evidence of chronic B.t. toxicity in dogs, guinea pigs, rats, humans, or other test animals.
- Fate in humans and animals: B.t. does not persist in the digestive systems of mammals that ingest it .
Why Do I Use Bacillus Thuringiensis (bt)?
How to Use Bascillus Thuringiensis in Your Garden?
- Purchase Bt via mail order or at from your local garden shop.
- Reading the directions for mixing.
- Purcahse an inexpensive 1 gallon sprayer.
- Mix Bt with water the day you are going to use it. (It is not effective to let it sit mixed for days.)
- Spray the outer and underside of your plants weekly.
- You may need to do it a 2nd time, in a week, if there is excess rain.
- Only spray the plants that are prone to caterpillars.