BT (Bacillus thuringiensis) for Natural Pest Control

caterpillar bt

Many of the pests that make a meal out of your tomato plants can be controlled by the judicious use of BT (Bacillus thuringiensis). BT, which is actually a microbial disease, is not toxic to people, animals, birds or even beneficial insects. It biologically targets tomato plant destroying pests including army worms, loopers, and the dreaded tomato hornworm. The larvae of the pest eats the BT, the spores dissolve releasing toxins into the bloodstream, the toxins multiply and the pest is poisoned. Thus you have a safe and natural “pesticide” which does not harm your tomatoes or the surrounding environment.

BT is actually a bacterial disease of insects commonly found in soil. Because some of the strains of these bacteria can kill insects, it has been developed for insect control. First discovered in 1911, it was not used much until the 1950’s and today with renewed interest in safer and better for the environment pest controls, BT has become much more widely used.

Scout to Know When to Apply BT

If BT is to work, you must time the application correctly. Because it is a stomach poison, the insects must eat it for it to be effective so you must treat when the caterpillars are actively feeding. Once they are fully grown, they move off the plants to make cocoons. Look under the leaves for masses of eggs. Flag those you find and check every day to see when they hatch. When all the masses have hatched, treat the plant with a product containing BT and recommended for caterpillars. Follow the directions carefully and be sure to spray or dust the undersides of the leaves. Daily scouting should be part of your plant care routine and if you suspect there may be a problem, begin by treating the soil. That is where the destructive worms are lurking.

Where to Buy BT?

There are over 100 BT products registered in the US. Two of the most common and generally readily available are Dipel Dust and Safer Brand Caterpillar Killer. Garden centers will generally carry several products containing BT. With any pesticide be sure to wear long sleeves, gloves, eye protection and a dust mask when making the applications.

Comments from Other Gardeners
  • healthnut says:

    How often do you recommend re-treating in order to get rid of the infestation? And should I continue to treat even after I don’t see any signs of them anymore, or is it a case of “if I don’t see them, there aren’t any?” I’ve only recently made the switch from standard chemicals to completely organic growing and am trying to learn everything at once!

  • Julie says:

    You should not have to apply it again if you applied it correctly the first time. BT is eaten by the caterpillar pests and tomato horn worms as they eat the leaves of the plant. Be sure apply when caterpillars are small and to spray the undersides because often that is where the worms are. Within hours of eating the BT, their insides become paralyzed and although they may take several days to die, they can’t eat any more. Sunlight caused BT to no longer be effective after a week but you shouldn’t need it any more.

  • Sea belle says:

    This maybe an odd question but if BT microbes can destroy the gut of insects, what can they do to the digestive system of humans?

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