by Erin Marissa Russell
Wondering about Bacillus Thuringiensis (Bt) and how it works as a pest control in the garden? Here’s a guide to tell you all about this organic pest control method that uses a naturally occurring, soil based bacteria to kill insect larvae that are susceptible to it.
Every gardener is familiar with the ongoing battle against pests of all kinds. You’ve worked hard planting and tending your garden, so it makes sense that you’d work just as hard to defend it. It’s a big job. No wonder Americans alone use 100 million pounds of pesticides each year to grow bigger tomatoes and cultivate lusher flowerbeds.
Why Use Botanical Bt for Insect Control?
That said, what doesn’t make sense to many gardeners is protecting plants that will feed your family by spraying them down with chemicals or treating soil with traditional insecticides. Widespread usage does not equal safety. A United Nations report explains that 200,000 people die each year due to toxic pesticide exposure. The UN report lists an array of health issues that experts suspect are linked to these treatments, including “cancer, Alzheimer’s and Parkinson’s disease, hormone disruption, birth defects, sterility, and neurological effects.”
Even if you aren’t growing food, you may be concerned about the effect your garden has on the earth and its creatures, wild and domestic. The National Pesticide Information Center provides a list of procedures for pet owners to follow to ensure the safety of their furry friends around chemical pesticides and insecticides. This can get complicated. As the NPIC’s precautions note, pets whose owners treat their yards with chemical insecticides face risks that may not come to mind immediately. These include coming into contact with chemically treated soil, being accidentally lured to pesticide bait by food ingredients, and eating poisoned prey animals. For these reasons and others, more and more gardeners are looking to natural ways to deflect the barrage of bugs in their backyard gardens without resorting to chemical treatments. And many of those gardeners are choosing botanical Bt, the most widely used microbial pesticide out there.
If going organic when it comes to pest control makes sense to you, botanical Bt is bound to be just the solution you’re looking for. It calls on naturally occurring microbes to defend your garden. The bacterium named Bacillus thuringiensis (which gardeners know better as “botanical Bt”) offers its own self-defense system. These microbes produce a protein that, when consumed by certain insect larva, is deadly. However, botanical Bt is safe for human consumption and can be used on crops all the way until harvesting time.
Four decades of putting botanical Bt to use has resulted in no cause for concern when it comes to human or environmental safety, according to the U.S. Environmental Protection Agency. It’s “practically nontoxic” to people and other vertebrates, with potential for minor irritation if it’s inhaled or gets in the eyes. Botanical Bt has no chronic toxicities, does not cause cancer, does not lead to chromosomal mutations, and has not caused birth defects in animals exposed to it.
In fact, botanical Bt doesn’t show up in the bodies of exposed people or animals, except for where you’d expect to find an edible substance (in the digestive system, where it’s harmless). The inert ingredients, preservatives, and volatile agents in botanical Bt also have not proven dangerous.
How Does Botanical Bt Kill Insects?
It’s pretty amazing that the bug-fighting weapon botanical Bt does its job completely naturally, but it’s true. The bacteria happen to produce a crystalline protein named δ-endotoxin that wreaks havoc on the gut lining of that Bt strain’s target bugs. These proteins cause splitting of the cell membranes in the bugs’ gut lining.
As a result, the gut wall breaks down, and the body is flooded with spores and the bacteria normally housed in the gut. These substances lead to septicemia, killing the target insects in larval form 24 to 48 hours after they feast.
Which Strains of Botanical Bt Kill Which Insects?
Different strains, or types, of botanical Bt are fatal to different insects. So far, researchers have found varieties of botanical Bt that work against moths and butterflies, beetles, and mosquitoes, and biting flies.
The following strains of botanical Bt are registered with the Environmental Protection Agency and readily available for commercial use.
- Bt aizawai targets lepidoptera (butterflies and moths). This strain is used in honeycombs to fight off wax moth larvae.
- Bt israelensis takes out insects of the order diptera (two-winged “true flies”). The israelensis strain has been instrumental in fighting mosquitoes, black flies, and fungus gnat larvae.
- Bt kurstaki is another lepidoptera fighter. It hones in on the population of gypsy moth, hornworm, cabbage worm or cabbage looper, tent caterpillar, spruce budworm, and many other common leaf-eating caterpillars and vegetable pests.
- Bt san diego and Bt tenebrionis will take out certain coleoptera (beetles). These types come into play when battling the elm leaf beetle and Colorado potato beetle on potatoes, tomatoes, eggplants, or elms.
- Bacillus popilliae kills off Japanese beetles with milky spore disease. It was the first botanical Bt product developed for commercial use.
More strains of botanical Bt have been isolated and studied but are not yet registered with the EPA or available for commercial use.
- Bt galleriae is another that works against coleoptera (beetles). It’s especially well known for fighting Japanese beetles.
- Bt japonensis and Bt kumamotoensis also combat coleoptera. These two strains have been reported effective against several species of turf beetle.
Strains of botanical Bt are continually being discovered that target different insect types. These experiments have found promising local isolates of botanical Bt that hone in on an area’s pest insects.
What Are the Limitations of Botanical Bt?
To be effective, botanical Bt must be consumed by the insect while in its larval form. That means gardeners who rely on Bt to protect their crops must be careful to coat the plants completely. It also limits bug-fighters to a certain window of opportunity.
Botanical Bt won’t make a dent in a population of adult insects or a clutch of aphid eggs, for example. And because insect larva tend to eat less in cold weather, a brisk, chilly day isn’t your best option for treating a garden with botanical Bt. But there are plenty of other organic and natural pest control options for those insects.
That window of opportunity also applies to Bt’s active period. Time spent sitting in the sun or water breaks down botanical Bt, so it’s most effective just after it’s applied. New formulations of botanical Bt are made to last longer and protect the bacteria from deactivation, however.
In addition, the very targeted nature that makes botanical Bt so effective against infestations of a particular insect can be a downside as well. If you’re looking for a really well-rounded, general pesticide and you’ve been struggling with a variety of bugs, botanical Bt may not be the way to go. Keep in mind, though, that the selective action of botanical Bt prevents scattershot killing of beneficial insects.
One class of pesticides, called neonicotinoids, has been having a trickle-down effect that the Yale Environment Review says could be connected to the decline in worldwide bee populations. We probably don’t need to stress to you as a gardener how important bees are to the health of food crops for humans. Other pesticides could be killing beetles, which prey on the slugs that can be so detrimental in the garden. The only beneficial insect that botanical Bt harms is the butterfly larva, so gardeners should take special care not to use Bt where butterfly larva feed.
Botanical Bt also isn’t an instant or 100-percent effective control measure. It takes time for Bt to harm bugs once it’s ingested. When larvae eat the Bt, they continue to live for a couple of days before they’re killed by it.
However, Bt-affected larvae do stop eating, which also puts an immediate stop to the damage to your plants. It’s also worth pointing out that not every single larva that munches on botanical Bt will die. Those who do, though, are more likely to die early due to environmental factors or small amounts of other insecticides that might not otherwise do them in.
Some insects are able to bounce back from Bt consumption by developing an immunity. For example, the diamondback moth, which is notorious for dodging gardeners’ attempts at extermination, is reportedly exempt from its dangers. Insects that have developed immunity, researchers say, are able to detoxify the protein quickly enough to avoid ill effects. However, these insects have proven not to reproduce well, limiting the effect this immunity has on the population long-term.
In short, if you’re facing a major influx of a certain type of pest and it’s a type targeted by one of the available strains of botanical Bt, chances are using it can do your garden a world of good.
The best part is how safe botanical Bt is for people, beneficial insects, birds, fish, pets, and other animals. When you choose to protect your garden with botanical Bt, you can rest easy knowing your kids, pets, and crops are safe—and that you’re doing your part to help ensure the health of our planet.
Want to learn more about Botanical Bt?
Brooklyn Botanic Garden covers Natural Pesticides
Gardening Know How covers Bt Pest Control
Gardening Know How covers Facts About Slugs and How to Kill Garden Slugs
Garden Safe covers Bt Worm and Caterpillar Killer
Yardener covers Using Bacillus Thuringiensis (Bt)
Mother Earth News covers How to Use Bt Pesticide
Planet Natural covers Bacillus thuringiensis Products
Washing State University covers Bt Biopesticides
Scientific American covers Pesticides That Kill Pests, But Not Pets
Today’s Homeowner covers Using Bt for Organic Caterpillar Control in Your Garden
Veggie Gardening Tips covers Bt: The Organic Caterpillar Control That Works Naturally
Does Bzt kill slugs?
Is Bt safe on leafy vegetables like lettuces?
How often should you spray with Bt? Also, is it safe to eat lettuces and other leafy vegetables after spraying with Bt or is there a recommended waiting period before doing so?
The label for the brand BT Now says, “BT NOW may be applied up to and on the day of harvest.”
BT can be used on fruits and vegetables and food crops.
If you search for BT pesticide label, you’ll see the instructions come up for most brands and their recommended application rates.
Is there any type of BT that will kill the milkweed weevil? They are wiping out several big patches of my friends purple, Common, & Swamp milkweed. Is there anything to help get rid of them? TY