The Rusted Garden Journal : KNOL: Controlling Leaf Eating Caterpillars with Bacillus Thuringiensis (Bt)

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)

by Gary Pilarchik LCSW-C

Is it Toxic to Humans and Other Wildlife?

You can read the entire artice at this link: Extoxnet.orst.edu

Below is a section of the document found at the above link. It details the toxicological effects of Bt. I recommend going to the link and reading the entire document. It will provide you with a clear understanding of the bacterium Bacillus Thuringiensis. It is important to understand the effects of the products you are using in your garden. You can use the information from this link, as one source , in determining whether or not you would use Bt in your garden. I also recommend a quick google search for additional information. I consider Bt to have a low level of toxicity and use it in my garden.

Toxicological Effects:

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 [146]. 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 [147]. 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 [148]. 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 [148]. 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 [149]. 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 [8]. 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 [143].
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. [143]. Dietary administration of B.t. for 13 weeks to rats at dosages of 8400 mg/kg/day did not produce toxic effects [143]. 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 [8].
Reproductive effects: There is no indication that B.t. causes reproductive effects [143].
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 [143]. 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 [148]. 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 [149].

The above information can be found a this link: Extoxnet.orst.edu. Extoxnet files are maintained and archived at Oregon State University.

Why Do I Use Bacillus Thuringiensis (bt)?

I have a problem with caterpillars... end of story. I found spraying on a weekly routine desimated the caterpillar population. I no longer had significant damage holes in my cabbages and kales. Well, not from the caterpillars anyway. It found it to be effective and I believe from my research it is safe. It is inexpensive, easily mixed and sprayed.

My Nemesis

This guy has been my nemesis in the garden for years. I was hesitant in using Bt because I figured I could hand pick them or try other means and I thought it was a poison. What I discovered was that I just didn't have the time to be as diligent as I needed. Hand picking helped when I could do it. But, I would miss 2 week periods at times and that's all the time my nemesis needed to hatch, grow and damage. I also opened, as another tactic, the garden planting area up a bit more to let in birds and other insects. This actually helped with slugs but I didn't notice any effect on the caterpillar's damage. I just ended up planting less crops. So I was losing on 2 ends. I planted less and the caterpillars continued to damage my crops.

I'm writing this Knol with the hope you take the time to research Bt and learn that it is not a man-made insecticide or poison. It is soil dwelling bacterium that is cultivated and used as a pesticide. The hardest time I had using Bt was finding it in garden shops. I could find poisons and insecticides but Bt was hard to find and often expensive when I did find it. The best way to find it is on-line.

How to Use Bascillus Thuringiensis in Your Garden?

I am going to make this simple. It is this easy.

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.

If you have knowledge about the caterpillers and moths in your area, you only need to spray during their active periods. I found it easier to start spraying in May in my area and to continue through August.