Bt – The Whole Story

Bt is a natural insect control which I recommend often on GardenLine. It can take care of many current problems with worm-, caterpillar-, and larvae-based insects. And that includes mosquito larvae control with Bt “dunks.”

When I started researching Bt, my brain almost went into shutdown mode because all the “scholarly” articles I found. An example: “Bacillus thuringiensis is a gram-positive, soil-dwelling bacterium, commonly used as a biological pesticide. B. thuringiensis also occurs naturally in the gut of caterpillars of various types of moths and butterflies, as well on leaf surfaces, aquatic environments, animal feces, insect-rich environments, and flour mills and grain-storage facilities. During sporulation, many Bt strains produce crystal proteins (proteinaceous inclusions), called δ-endotoxins, that have insecticidal action. This has led to their use as insecticides, and more recently to genetically modified crops using Bt genes, such as Bt corn.” Blah, blah, blah…….and ugh!

Let me simplify this for you. First, I always call it “Bt” and explain it stands for Bacillus thuringiensis. But I don’t expect you to remember the pronunciation or the spelling. Bt is a naturally occurring organic bacterium that is toxic to worms or caterpillars. They get sick and die immediately after biting into anything treated with it. Planet Natural has a more detailed but easy-to-understand article on it.

You will see Bt-based products in liquid form under the commercial name Thuricide. And you will find Bt dusts listed as DiPel. Almost every garden-care line makes a Bt product, but they don’t always use the words Thuricide, DiPel or even Bt on the label. So look for Bacillus thuringiensis among the active ingredients.

I’m not going to list the scores of worms, caterpillars and larvae this organic product will control, but everyone in Southeast Texas should be on the lookout for about five specific infestations that can be easily tackled with Bt products. Best of all, Bt is perfectly safe for many beneficial insects, including bees.

After any heavy rain, Bt mosquito dunks, or donuts, are probably best line of defense in controlling those pests. Just drop them in standing water, where mosquitoes breed and lay their eggs. With a Bt-infused donut present, the larvae will never mature to a biting adults. 

When tent caterpillars, oak leaf rollers and other worms and caterpillars are observed devouring leaves on trees, spray a liquid Bt on as many leaves as possible, and the critters will be poisoned immediately.  It will also eliminate those hungry tomato hornworms in vegetable gardens. They can devour a crop in no time. Treat the plants with liquid Bt, and they’ll be protected for 30 days.  If your sweet corn crop suffers from corn borers, this product is a life-saver. And if you’re plagued by squash vine borers, inject Bt into the bottom of the plant where the moth lays eggs. They’ll never make it to maturity.

Finally, my research found that Bt could be a great control for fungal gnats. None of the references I found made it clear which form – liquid or powdered – was used, but I’m guessing that powdered versions like DiPel dusted on places where the gnats are breeding would be best. If you’ve had success in fungal gnat control, please send me an email or add a Facebook comment.