What Is Bacillus Thuringiensis, How Do You Use It In The Garden?

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Bacillus Thuringiensis (Bt) is very safe and very effective, like the natural insecticide for plants neem oil that helps control your caterpillar problem without harming your friendly fauna.

In this article, we will share some smart tips to help you use this species-specific bacteria to its best result in your garden. Read on to learn more about what are bt sprays.

What Is Bacillus Thuringiensis, How Do You Use It In The Garden?Pin
Bt good to control little green caterpillars eating plants | brianjones-BigStock

How Does Bacillus Thuringiensis (Bt) Work?

This type of Gram-positive bacteria is always present in soil. It contains crystallized insecticidal proteins called parasporal crystals forming around spores of the bacillus thuringiensis and bacillus sphaericus bacteria acting as a toxic precursor. When caterpillars eat these bt products, the proteins in the bacteria act to paralyze the digestive system.

This naturally occurring bacteria is available for use in several different strains. It is deadly to caterpillars of all kinds but has no effect on other insect pests in your garden. Many different garden pests classify as caterpillars, so the use of Bt can be very beneficial, indeed. You do want to take care not to use it in areas of your garden where butterfly caterpillars are present, though!

Will It Harm People or Animals?

Even though it is effective pest management and deadly to caterpillars, bt toxin is harmless to most beneficial insects as well as animals and people. You can use it in your vegetable garden on the very day you harvest, but do remember to wash your produce before you eat it.

Choosing The Right Kind Of Bacillus Thuringiensis Bt

You can purchase this product as a liquid bt, a powder or a bait. Strains include:

1. Bacillus thuringiensis kurstaki (Btk)

Bt kurstaki is an excellent choice when dealing with tomato hornworms, cabbage worms or cabbage looper and other leaf-eating caterpillars. When you apply it to the leaves the caterpillars will eat, they ingest it and it ruptures their guts causing death.

Insects that do not eat the leaves you have treated are not affected by bacillus thuringiensis var kurstaki at all. This makes it (bt for caterpillars) a very effective pest control and safe deterrent for caterpillar pests such as:

BT caterpillar killer is an amazing product!

2. Bacillus thuringiensis israelensis (Bti)

Bacillus thuringiensis var israelensis strain is helpful in controlling fungus gnats, which often plague houseplants and greenhouse plants. Its insecticidal activity is also very good for controlling mosquito larvae including aedes aegypti and diptera culicidae in standing water when it is not possible to introduce fish to control them.

Bacillus thuringiensis subsp israelensis is the effective ingredient in mosquito dunks. It is also very effective against black flies. This strain is best used to drench the soil to control army worm or to treat standing water. It should not be used as a foliar spray.

3. Bacillus thuringiensis Bt (var. tenebrionis/San Diego)

This particular strain is a specialized one developed to target:

  • Cottonwood leaf beetle
  • Elm leaf beetle
  • Potato tuberworm
  • Potato beetle

Getting Bt That Is Certified As Organic

If you are concerned about using genetically modified products, be especially careful in reading the packaging. There are some manufacturers that use strains of the bacteria that have been genetically modified.

To be sure of getting only naturally occurring strains, consult the list maintained by the Organic Materials Review Institute (OMRI).

This list will give you sources for organic products or bt insecticides made from non-GMO strains of the bacteria. If you are striving to grow organic produce, you will want to be especially careful about this. It is easiest to find non-GMO Bt in its powdered form.

Bacillus Thuringiensis Uses: The Pests Affected 

When applied early, before caterpillars have had a chance to attain much growth, Bacillus Thuringiensis larvicidal activity can be very effective in controlling caterpillar eating leaves such as:

Tips For Using Bt Effectively

Timing is everything when applying Bacillus Thuringiensis. Remember that sunlight causes it to degrade, so to get the most out of it you should apply it at sunset. Another good reason for a late afternoon application is that caterpillars tend to feed in the evening.

When placing your Bt, be sure to put it in areas where you have seen caterpillar activity. For example, if you are targeting corn earworms, you should apply your solution of Bt to the tips of your ears of corn.

You should never simply broadcast it because it will kill of beneficial butterfly caterpillars just as effectively as it does destructive, crop and lawn eating caterpillars. Apply with care and caution.

Time your application so that it will have a full 24 hours in place. Don’t apply it just before rainfall. You will want to repeat your application every ten days until your problem is resolved.

Learn more about Controlling Caterpillars Eating My Leaves

Mix & Store Your Bt Correctly For Best Results

Mixing directions vary from one manufacturer to another. Remember to always read packaging instructions to be sure of creating the most effective and safest mixture. When you mix your solution, you should only mix as much as you will use within a few days. If you have any left over, mix it with water and pour it onto the ground or pavement in a sunny area.

Store the undiluted concentrate in its original container in a locked cupboard and/or on a high shelf. It should not be accessible to children, pets or livestock.

Guard your concentrate against extremes in temperature. It should stay consistently cool. If temperatures exceed 100 degrees Fahrenheit, your product will be ruined.

If you store Bt powder correctly, you can keep it on hand for many years. The liquid does not have quite as long a shelf life. You should not keep it longer than three years.

How To Apply Bacillus Thuringiensis Spray

Think of Bt like penicillin. You should avoid overusing it because if it is consistently present, caterpillars will eventually build up a resistance to it. In order to ensure that Bt continues to be a valuable pest control tool, it must be used carefully and judiciously.

This natural pest deterrent can be applied as a liquid bt or a powder; however, you will have more control over a liquid solution. Instead of broadcasting the product, follow packaging directions to mix up your solution. Put the resulting dilute mixture into a small spray bottle. Apply it judiciously to affected plant foliage.

Carefully apply your mixture to the tops and undersides of leaves where caterpillars have been feeding. Coat the leaves lightly and evenly. A heavy coating is not necessary, and you want to avoid runoff and drips.

Don’t Expect Instant Results

It can take several days to see a change in your caterpillar population, and you must remember to make regular applications every ten days until your problem is resolved.

Defend Butterfly Caterpillars Against Bt

It is important to understand that every species of butterfly caterpillar feeds on a specific type of plant. Monarch caterpillars, for example, only eat milkweed. To be sure of having abundant butterflies, you must avoid spraying plants their larvae consume.

Be very careful to only target problem caterpillars. Treat only the plants eaten by pest caterpillars and apply the product carefully and sparingly. They only need a mouthful each to kill them! You do not want to negatively impact butterfly caterpillars as they grow up to be valuable pollinators.

Sources: 1 | 2

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