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How to Manage Pests

Pesticide Information

Active ingredient: Bacillus thuringiensis ssp. kurstaki

Pesticide type: insecticide (microbial)

Synonym: Bacillus thuringiensis

See example products below.

Potential Hazard1 to
Water quality2
(aquatic wildlife)
Natural enemies
Honey bees3 People and Other Mammals
Acute4 Long Term5
Not listed

Acute Toxicity to People and Other Mammals4

  • Toxicity rating: Not Acutely Toxic

Long-Term Toxicity to People and Other Mammals5

  • On US EPA list: Not listed;
  • On CA Proposition 65 list: Not listed

Water Quality Rating2

  • Absorbed runoff toxicity risk to fish rating: Low
  • Solution runoff toxicity risk to fish rating: Low
  • Source: UC IPM WaterTox Database (originally NRCS Pesticide Properties Database)

Impact on Natural Enemies

  • Overall toxicity rating: Low
  • Specific impacts: predatory mites (Low), parasitoids (Low), general predators (Low)

Impact on Honey Bees3

  • Toxicity category: IV - Apply at any time with reasonable safety to bees

Pests for which it is mentioned in Pest Notes

Biological Control and Natural EnemiesCalifornia OakwormLawn insectsLeafrollers on Ornamental and Fruit TreesRedhumped caterpillarRoses in the Garden and Landscape: Insect and Mite Pests and Beneficialscaterpillars

Application Tips

Surfaces where caterpillars feed must be well covered because caterpillars must ingest the bacteria to be affected. Careful timing is essential for success. Apply just after caterpillars begin hatching out of eggs. Small caterpillars are more susceptible than older larvae. Treatment is not effective on eggs, pupae, and adults. The material breaks down rapidly in the environment. Try to avoid making applications when the sun is on the plant. Affected caterpillars will stop feeding within hours, but may not die for 2 to 3 days. Wettable powders that you mix up yourself just prior to application will be most effective. Make up a fresh solution each time you treat. Reapplication will be necessary to kill caterpillars hatching one or more days after an application is made.

Precautions and Safety Equipment

Minimize your exposure to pesticides.  Avoid contact with eyes.  Wear eye protection, long pants, a long-sleeved shirt, and a hat that can be washed after each use.  Always read label of individual product for additional directions.

Always check the label before purchasing or applying a pesticide product for a specific pest on a specific plant to be sure it can be applied. Follow label directions precisely.


Example home, garden or landscape use products6

Garden Safe Brand Bt Worm & Caterpillar Killer


  1. Potential Hazard Rating: VL=Very low, L=Low, LM=Low to Moderate, M=Moderate, LH=Low to High, MH=Moderate to High, H=High, VH=Very High, N=None, NKR=No Known Risk, —=No data
  2. Water quality ratings from Pesticide Choice: Best Management Practice (BMP) for Protecting Surface Water Quality in Agriculture, ANR Publication 8161, or the USDA-NRCS WIN-PST database—see Pesticides: Water-Related Toxicology of Active Ingredients.
  3. Honey bee ratings are: (Very High) I-Do not apply to blooming plants; (High) II-Apply only during late evening; (Moderate) III-Apply only during late evening, night, or early morning; and (Low) IV-Apply at any time with reasonable safety to bees. For more information, see How to Reduce Bee Poisoning From Pesticides (PDF), Pacific Northwest Extension Publication PNW591.
  4. Acute oral toxicity ratings for people and other mammals based on LD50 and US EPA Acute Toxicity Ratings system: H = Highly Toxic (LD50 <50), M = Moderately Toxic (LD50: 50-500), L = Slightly Toxic (LD50: 500-5000), VL = Not Acutely Toxic (LD50 >5000)
  5. Long term ratings indicate whether the active ingredient is on the California Prop 65 list, which indicates if materials are known to cause cancer or reproductive toxicity, or whether the US EPA has classified the pesticide as "likely to be carcinogenic to humans", "Group B-Probably Human Carcinogen", or "Group C-Possible Human Carcinogen."
  6. These products were registered for home and garden use in California in July 2013. Professional use products are not included. If no example products are listed, this active ingredient may be available only for professional use. Individual products are registered for specific uses on specific sites. Read the label to determine if the product is registered for your use. Note that some products may be formulated with additional pesticides.

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Statewide IPM Program, Agriculture and Natural Resources, University of California
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