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What is Bt and can it be Used for Organic Pest Control?

Bacillus thuringiensis, also known as Bt, is an organic insecticide. Many have reservations when it comes to insecticides, especially since they are known to cause harm. So, before you buy Bt and use it in your yard, you probably have some questions. Is it truly organic? Will it even work?

Bacillus thuringiensis (Bt) is a soil bacterium that is used for organic pest control. Used since the 1950s, it is effective at killing a wide variety of pests, and it is trusted by many organic farms. If you are looking to use an organic pesticide, then Bt is a viable option for you.

Bt is a great option for those looking for organic, eco-friendly pest maintenance. There is a lot that goes into this natural bug killer, though, so I encourage you to read on so you learn all you can before making a final decision on what is best for you and your garden.

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Photo by Lovelyday12

What is Bt pest control?

Bt pest control is the use of the naturally occurring Bacillus thuringiensis bacterium to kill harmful pests.

Bacillus thuringiensis is a soil-borne bacteria that consists of a “spore, which gives it persistence, and a protein crystal within the spore, which is toxic.”

The toxic crystal within the spore is what will kill the pests. When the pest eats the bacteria, they break down the spore. This causes the crystal to release into their gut, which is highly alkaline. As a result, the pest is essentially poisoned and dies.

You can use Bt on things such as produce plants in your garden, in standing water environments, and it can even be used in food storage such as grain bins.

Since Bt poisons pests to kill them, you might wonder whether it’s safe to use Bt on produce, as it might be harmful for humans and animas to ingest.

The good news is that Bt is completely safe! The acidic gut of animals like fish, birds, cats, humans and other mammals negates the negative effect of the bacteria. As a result, they will not be poisoned by the spore or crystal, and their stomach will not be injured!

Is Bt considered an insecticide?

An insecticide is a pesticide made to ward off or kill insects. They can come in many forms such as, sprays, dusts, gels, and baits.

Due to this definition, Bacillus thuringiensis is categorized as an insecticide. Just like all insecticides, it targets certain pests. Because of this, while it is effective in killing certain bugs, it will be ineffective against others. 

So, if you can determine what pests are most troublesome in your yard, you can decide whether or not Bt is right for you. 

What is Bt Effective at Killing?

There are a variety of pests that Bt is effective at killing.

Some of the most common things that it is used to kill are leaf eating pests such as:

  • Caterpillars
  • Gypsy moths
  • Cabbage loopers
  • Tomato hornworms

Bt can also be used to kill pests such as:

  • Mosquitos
  • Black flies
  • Fungus gnat larvae
  • Leaf-eating beetles
  • Japanese beetle larvae

As you can see, Bt is effective against a wide variety of pests that may plague your yard. That is why so many organic farmers and gardeners use Bt as their insecticide of choice.

Is Bt a Form of Organic Pest Control?

In general, most Bacillus thuringiensis products are organic because it is derived from soil bacterium.

Despite the fact that many Bt brands are organic, there are some brands that add extra properties and thus they are genetically modified. Some brands that are not organic include:

  • Crymax: subspecies kurstaki
  • Condor: subspecies kurstaki
  • Leponix: subspecies kurstaki
  • Novodor: subspecies tenebrionis

If you want stay organic, watch out for these brands and always check the label before you buy any Bt to ensure you only buy something that specifically states it is organic.

Can Bt be Used in Organic Farming?

In most cases, Bt can be used in organic farming since it is naturally found in soil. In fact, Bacillus thuringiensis has been used in organic farming since the 1950s and potentially as far back as the 1920s.

If you use a non-organic form of it, though, then it would be falling out of the range of organic farming. To make sure that you are within the guidelines for organic farming, review and follow these USDA guidelines.

Does Bt Count as Certified Organic?

According to the USDA, some forms of Bt are certified organic. Most of the time, organic Bt will come in a powdered form. You will know whether Bt is organic by looking for the Organic Materials Research Institute (OMRI) certification stamp.

Unfortunately, as noted above, some Bt products are genetically modified and some (but not all) of the liquid brands are mixed with a non-organic solvent.

Because of this, if you are running an organic farm or garden, you need to be careful when using Bt, making sure that you are not using a non-organic version. 

What is Bt Commonly Used for?

Bt can be used in many different applications, depending on the strain that you use.

Bt is most often used as an insecticide that is for both commercial use and personal use.

In both cases, it is used to protect against pests such as caterpillars and beetles that eat plants and produce. For the farmer, this means that their crops will be protected and will have a good produce yield. For home grower, this means that their gardens will stay looking nice, and their hard work won’t go to waste.

Bt can also be used in another area too!

If you have issues with mosquitos in your yard, then Bt israelensis can be sprayed in standing water to kill the larva. As long as they are killed in the larva stage, your issues with mosquitos should diminish because they will die before they can even reproduce. 

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Photo by Hollyharryoz

How and When to Use Bt

Now that you know some of the basics of Bt and how it works, here are some tips on how and when to use it. 

If you have a small garden, then the powdered form is a viable option for you. All you need to do is sprinkle the leaves of your plants with the powder, leaving a light film on them. Make sure to apply enough so that the pests will eat the insecticide. This YouTube video gives a good visual of what you should aim for.

If you have a larger area to cover, the liquid form might be better suited for your needs. The liquid form comes in either a wettable powder that you need to mix, or a premixed liquid. If going this route, make sure you are using the wettable powder and not the dust. To apply Bt in its liquid form:

  • Make sure to shake the bottle to keep the formulation at suspension
  • Spray the tops and bottoms of the leaves
  • You will know you have applied enough when the liquid is running off the leaves. The video above also gives a visual demonstration of what this looks like.

To control a mosquito problem, all you need to do is spray standing bodies of water with an organic liquid spray. Make sure the spray is organic, especially if you are spraying into something like a lake because non-organic variants could harm marine life.

In addition to knowing how to use Bt, you should also know when to use it so that it can be most effective. 

  • Try to apply it in the larval stages of the pest’s life as soon as you notice they have infected your garden since Bt is most effective at an early stage. In fact, some Bt products won’t even work once the pests reach a certain level of maturity.
  • Try not to apply it in sunlight, because it degrades quickly in the sun.
  • Make sure to reapply it after about a week because that is about how long it takes to degrade. Reapply until the pests are gone.

Does BT have a Shelf Life?

Like all products, Bt does have a shelf life and unfortunately, the shelf life is shorter than other types of insecticide. 

Despite this, Bt’s shelf life is still quite long, lasting for about two to three years when stored properly.  To make sure it lasts closer to three years, store it in a cool and dry place that is not in direct sunlight.

In any case, if you need to use it on a frequent basis, chances are you will run out before it expires. So, you do not have to worry about the Bt and the money you spend on it, going to waste.

Are there any Downsides to Using Bt?

For most of this article, we have been talking about all the benefits of Bacillus thuringiensis such as how it is often organic and can protect your garden from invasive pests. Despite this, you may be wondering if there are any downsides to using Bt.

So that you have a full understanding of this product, we will talk about some controversies that have popped up around Bt. That way, you can determine whether the product is right for you.

Controversies to Consider

The United States EPA classifies Bt as Generally Regarded as Safe (GARS).  Despite this classification, there is some research from outside of the U.S. that suggest that it may have some harmful effects.

For example, a study out of the European Union suggests spraying genetically engineered soybeans with Bt could cause a variety of issues, such as potential enhanced toxicity due to “combinatorial effects between plant components and other impact factors.”

There is also evidence out of India that using genetically modified Bt seeds may harm farm management. For example, Indian farmers who used genetically modified Bt cotton seeds saw higher yields, but these were generally the well-financed farmers who already had good output. 

It should also be noted that some pests can grow resistance to Bt seeds, thus they eventually do not help in warding off infestations. Although new seeds come out to combat this, the study out of India found that it changes at such a pace that many farmers cannot keep up with the changes.

How Long does Bt Take to Kill Pests?

So, Bt does work, and it is organic. But how long does it take to go into effect and kill the pests plaguing your yard?

In most cases, once the spore has been ingested by an insect, the insect will stop eating within just a few minutes. After this occurs, it takes about two to five days for the pest to die. If you are using Bt to kill mosquitos, they should die within 24 hours.

If they do not die within this time frame, there may be a few issues that you are facing:

  • More pests have infested your plants since you sprayed.
  • You applied the Bt too late, and the insects have matured enough so that the Bt does not affect them.
  • The pests you are facing have gained resistance to the strain of Bt you are using.

For the first two points, as long as you keep up with treating your plants, these issues should not occur.

If you run into the unlikely issue of pests that have gained resistance to the Bt strain that you use, consult with a specialist to see what your best course of action should be to get rid of the pests.

Which type of BT should you buy?

The type of BT that you should buy is really determined by the type of pest that you are facing.

There are several different strains of Bt, and each one is effective at killing different types of pests.  Below, we will look at these different variants and what kind of bugs they target.

  • Bt kurstaki (Bt-k): This variant kills leaf-eating caterpillars and is most effective when it is applied in the 1st and 2nd instar (development stages) of the caterpillar’s life. The downside is that it degrades quickly when it is in the sunlight, so, if you have lots of insects to take care of, you may need to reapply it a few times.
  • Bt israelensis (Bt-i): this is best when used to get rid of mosquitos, black flies, and fungus gnat larvae. It can be applied to any place with standing water, such as a ditch, pond, or flowerpot. It kills these pests quickly too, with 95-100 percent dying within 24 hours.
  • Bt san diego (Bt-sd) and BT tenebrionis (BT-t): These strains kill certain types of beetles.  Unfortunately, they are only effective at the larval stages, and there has been research to show that many pests are gaining resistance to them.

So, before anything, you will want to determine what kind of pest is causing harm to determine which Bt strain will be the most effective for your needs.

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Photo by Kumar7075

What are Some Alternatives to BT?

Maybe you have used Bt in the past, and it hasn’t worked for you or maybe you are unsure about using it due to some of the controversies, or maybe you just want a backup plan in case Bt doesn’t work for you. Whatever the case may be, it never hurts to have some alternative insecticide options in the back of your mind.

Here are some alternatives to Bt to keep in mind:

  • Beneficial Nematodes: Nematodes are microscopic organisms that attack insects, often the larvae of beetles. When they enter the pest, they release bacterium that multiplies and kills it. 
  • Diatomaceous Earth (DE): fossilized remains of microscopic aquatic organisms. They do not need to be ingested; they simply dehydrate the pest. It does have to stay dry, though. Make sure to wear a respirator and other PPE if you use it as it can be harmful to breathe.
  • Grasshopper Bait: If you are having issues with grasshoppers, this may be the way to go.  Grasshopper bait has a natural fungi Nosema locustae that help control grasshoppers. The spores of this are attached to wheat bran. When the grasshoppers eat this, they get sick and eat less, eventually dying. It is slow acting, though, and best over a long period of time.
  • Milky Spores Paenibacillus popilliae (formally Bacillus popilliae): this is a bacterium that also lives in the soil. It kills pests such as the Japanese beetle and beetle grubs. It should be administered in a soil drench so that it soaks into the soil, killing these ground dwellers.  Unfortunately, though, it is not effective against adult pests.
  • Neem Oil: Neem oil can be used to naturally prevent pests and fungal infections, get rid of active pest infestations, and provide additional nutrients. This oil extract from neem tree seeds found on the Indian subcontinent has been used as a natural pesticide and fungicide for millennia.
  • Pesticidal Soaps: These soap salts, in their liquid form, must come into direct contact with the pest. If this happens, the insect will be suffocated. They work best against soft-bodied insects rather than hard bodied ones like beetles.
  • Pyrethrins: Derived from the chrysanthemum flower, these cause hyper excitation in the nervous system, quickly killing the pest after they eat or come into contact with it. Be careful though, as some people and dogs can have an allergic reaction to them, and they can harm beneficial insects like bees. If you use this, use it as minimally as possible.

If you use any of these alternatives, the most important thing to remember is to read the label and the instructions. They often have important information, such as what it is toxic to and if you need PPE while administering it. 

If you are selling your food as organic, make sure to confirm that whatever you use is within organic boundaries. Information like this can be obtained through places such as local farm groups and agricultural departments.

Other commonly asked BT questions

Now that most of the major information about Bt has been covered, we will go over a few common questions that many people have about the product. These are regarding the effect that it will have on other insects and animals, other than the ones it is made to target.

Is Bt Safe for Dogs?

Most lawn treatments are harmful to dogs due to their toxicity. But the good news is that Bt is safe for dogs!

In fact, it is a great dog-safe alternative to the toxic chemicals that are usually used to treat yards and gardens.

Is BT Harmful to Bees?

Another reservation you may have is whether or not it will harm bees. After all, bees are helpful, and you don’t want to kill them.

The great thing about Bt is that, in most cases, it is not harmful to bees, so you do not have to worry about hurting our little pollinators. In fact, it is so safe to use that you can use it when bees are present. One of the big reasons that it is safe is because of how quickly it breaks down. 

It should be noted though that the aizawai strain has been shown in some studies to be toxic to honeybees.

Is BT Harmful to Earthworms?

Studies seem to suggest that Bt does not have any negative effects on earthworms.

Is BT Harmful to Birds?

Bt is not toxic to birds either. So, if you have a lot of birds in your yard, you don’t have to worry about them being adversely affected by this insecticide.

Is BT Corn Harmful to Eat?

As of now, scientists have not found any evidence linking adverse health effects to Bt corn. Since human stomachs can digest the bacterium in Bt, there should not be any reason to worry about it affecting you.

Is BT Cotton Harmful?

Bt cotton does not have a negative effect on human health.

The only potentially harmful effect that Bt has on humans is a potential allergic reaction. It seems that this allergic reaction is in the case of coming into direct contact with the powder, seed, or liquid though.

Does BT (Bacillus thuringiensis) kill these 22 things?

Before we wrap up this article, we will go over 22 common bugs that you find in your yard, both harmful and non-harmful, and note whether Bt will have an effect on them. Hopefully, this final bit of information will help you determine whether Bt is right for you and your garden.

Insect TypeBt Kills ThemBt Does Not Kill Them
Spider Mites X
Monarch CaterpillarsX 
Fungus GnatsX 
Slugs X
Thrips X
Whiteflies X
Mealybugs X
Ants X
Earthworms X
Stink Bugs X
Snails X
Squash Bugs X
Tomato HornwormsX 
Wasps X
Cabbage WormsX 

As you can see, Bt is not harmful to everything in your garden, which is good because it means that pollinators and other beneficial insects will be relatively safe.

On the other hand, though, it means that some pests that are harmful will not be affected by Bt.

If you have other harmful pests in your yard or farm that are not affected by Bt, research to find what will kill them. That way, your plants will survive and won’t die due to these pests that can survive Bt. Be sure to check out our post on some organic way to handle pests.

Closing Thoughts

In the day and age of synthetic plant treatments, it can be hard to keep an organic yard or farm.

But, by using Bt, you can stay on that organic path.

The best thing is that Bt generally only harms target pests. Most studies show that mammals, and most non-target insects are not affected by the bacterium in Bt.

If you want to use Bt, it can be purchased at stores such as Home Depot and many plant nurseries will have it too. Just make sure that the Bt you buy is certified organic. Also, make sure that you thoroughly read the label, because it will have important instructions on application and any PPE that is needed. 

Hopefully, Bt will fix the parasite issues that you have, making your plants and produce bloom like never before!