Bt: the Organic Caterpillar Control that Works Naturally

Bacillus thuringiensis (B.t.) has been a godsend in battles with destructive caterpillars out in the vegetable garden. One of the most impressive things about Bt (aka Thuricide or Dipel), is that it targets and eliminates bad bugs without harming the non-targeted beneficial insects and pollinators.

B.t. accomplishes this feat because it is based upon a naturally occurring soil bacteria that operates like a stomach virus in causing caterpillars to become sick, quickly stop feeding, and die within days of ingesting even a small amount of the substance. How does that sound — a “bug” for bugs!

Other things that I like about using Bacillus thuringiensis for organic insect control in the vegetable garden include the following features and advantages:

• Ease of Application – B.t. comes in powered or liquid form. The powder can be dusted onto the plants or sometimes comes in a shaker type dispenser. The liquid version of B.t. is my favorite and is simply mixed with water and sprayed onto your veggie plants.

• Extremely Economical – One reason for my preference of the liquid version of Bt is that it seems to be more economical and a small bottle will go a long way. Kept cool and dry, Bt can be stored over a couple seasons, but I only mix up as much as I need for each application. You should be able to locate an 8 oz. bottle of B.t. for around $10.

• Very Effective – For the usual offenders in the garden Bt has never failed to not just control, but to totally eliminate the pests from my gardens. At the top of my hit list are cabbage worms that attack the heirloom cabbages, kale, broccoli, and other cole crops as summer winds down.

• Bugs Can’t Hide – It only takes a very small amount of Bt in the insect’s system to bring about its downfall, but they must ingest the bacteria in order for it to work. That’s usually not a problem as long as you provide good spray coverage during application.

• Safety Considerations –B.t. is a naturally occurring substance that targets specific insects, which makes it less intrusive on the environment than a broadly toxic pesticide, even the organic types. There are various strains for different insect types; B.t. Kursaki for caterpillar control, B.t. Israelensis for eliminating fly and mosquito larvae, and B.t. San Diego for controlling beetles.

Bacillus thuringiensis is available for use in destroying tent caterpillars, cabbage loopers, cutworms, gypsy moth larvae, budworms, corn borers, tomato hornworms, leafrollers, peach tree borers, webworms, codling moths, and other caterpillars. B.t. is also available for controlling the larvae of black flies, mosquitoes, and fungus gnats, in addition to potato beetles and certain leaf beetles.

Even though B.t. can be safely applied right up to the day of harvest, if there are only a few caterpillars to be dealt with, I still prefer the manual organic control of hand picking instead of breaking out the sprayer or duster. Apply Bt only when there is a definite need to control an identified and targeted insect pest that is present in the garden.

Potential Shortcomings of Using B.t. in the Garden

It sounds all good, but is there a downside to using Bt for organic insect control? Nothing major that I can think of, of course I do treat Bt with the same cautions as any other organic or chemical pesticide. Biological or organic doesn’t infer that a product can be handled haphazardly or be applied without restraint!

B.t. gradually breaks down over time and under exposure to sunlight, and more rapidly due to rainfall, so this biological insecticide will need to be reapplied after a week or two if the insect infestation continues. But in my experience I have usually been able to get by when needed with just a couple, well-timed, applications to control cabbage worms in the fall vegetable garden.

Possibly the biggest issue related to Bt is the potential for future insect populations developing a resistance to Bacillus Thuringiensis. Even though B.t. has been used effectively for decades there have been reports of insects developing a resistance and concerns that commercial attempts at genetic engineering to combine B.t. genes with plants will increase the threat of B.t. resistant insects.