Bacillus amyloliquefaciens (BAA) is a type of bacteria found in soil all over the world and also on dried foods and fresh produce.
Many strains of these bacteria promote plant growth and inhibit plant pathogens, significantly improving plant health. They colonize the roots of plants and reduce plant diseases through both direct and indirect action.
BAA strains produce a number of chemicals, including some antibiotics, that inhibit fungal spore germination and growth.
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In addition, the bacteria stimulate the plant to activate its natural defense mechanisms. This provides additional control of pathogens.
Many strains of BAA are so useful to plants that they are known as plant growth-promoting rhizobacteria (PGPR) – a designation for powerful bacteria that improve plant health.
In this guide, we look at how Bacillus amyloliquefaciens can improve plant health and provide tips on how to use these biological control agents.
BAA strains vary in their properties
Like the closely related bacterium Bacillus subtilis, B. amyloliquefaciens consists of many different strains, which differ in their production of antibiotics and their ability to colonize plants.
A dizzying array of strains has been researched, but most commercial formulations consist of a few key strains, especially D747 (often sold as Double Nickel or Stargus).
The powerhouse FZB42 sold commercially turns out to be a different species of Bacillus and is now known as B. venezensis.
How can BAA help your garden?
The biopesticide BAA can help prevent damage from pathogens and act as a biofertilizer.
These bacteria live in a prime location – they are components of the rhizosphere – the lush area around plant roots where the plants secrete sugars and vitamins that aid the growth of the microbes in this area.
In addition, a number of companies sell BAA to combat various plant parasitic nematodes.
The bacteria colonize plant roots
BAA starts its growth on the primary roots. First, it grows under the outer cells. Then it spreads along the root surfaces.
By being in this key location, the bacteria blocks the growth of pathogens on the roots.
The plants also benefit from the presence of BAA because these bacteria produce substances that stimulate plant growth and are absorbed by the roots.
This makes these bacteria plant growth-promoting rhizobacteria (PGPR) – just like their close relative Bacillus subtilis.
The end result is that plants grow better due to the fertilization provided by the bacteria. They supply both nitrogen and phosphorus.
In addition, BAA activates the plant’s own immune system, which is active throughout the plant. This helps the plant ward off foliar pathogens.
BAA defeats other microbes
These bacteria use different mechanisms that allow them to prevail over other microbes in the soil. First, they fix important nutrients that other organisms need to survive.
For example, iron is necessary for growth and is present in the soil in low concentrations. BAA produces compounds called siderophores that bind the iron and prevent other microbes from accessing it.
They also produce antibiotics that attack other microbes. Like Bacillus subtilis, BAA produces compounds such as iturins and fengmycin that inhibit the germination of fungal spores and the development of the fungal germ tubes.
In addition, the bacteria produce enzymes that break down other microbes! BAA can produce antibiotics that dissolve other bacteria. And some strains produce chitinases – enzymes that break down fungal cell walls made of chitin.
Bacillus amyloliquefaciens is highly resistant to chemicals
These bacteria have another advantage over other soil bacteria: they are unusually resistant to the chemicals plants produce to defend themselves.
Not only that – they are also normally unaffected by nematicides, herbicides and most fungicides.
They can be affected by antibiotics used to fight plant pathogenic bacteria, but these compounds are usually applied only to the leaves of apple or pear to fight fire blight.
Foliar antibiotic applications are highly unlikely to affect soil inoculants.
BAA is safe for humans and other organisms
Since BAA is a common soil dweller and occurs naturally on fresh produce, it is likely that humans are exposed to it on a regular basis.
The species is not known to produce toxins that affect mammals and has never been associated with outbreaks of foodborne illness.
Extensive testing for registration of strain D747 as a pesticide with the Environmental Protection Agency (EPA) found no effect on non-target organisms, including rats, fish, honey bees and plants.
The only PPE requirements are for pesticide handlers who are often exposed to the stress for extended periods of time. They are required to wear long-sleeved shirts, a dust/mist filter mask and waterproof gloves.
Plant pathogens targeted by Bacillus amyloliquefaciens
This organism affects a range of fungal and bacterial pathogens. The original EPA filing lists both soil pathogens and foliar pathogens.
Soil-borne fungal pathogens include Fusarium, Pythium, Rhizoctonia, Phytophthora and Verticillium, while foliar fungi include various rusts, powdery mildew, downy mildew, Botrytis cinerea and Alternaria.
Leaf bacterial pathogens include Pseudomonas syringae pv. tomato and Xanthomonas. In Canada, the species is registered for use as a preventative measure to control fire blight.
How to apply BAA to prevent plant diseases
While B. amyloliquefaciens does not cure plant diseases, some of them can occur on vegetables, turf, fruit trees, ornamentals, and greenhouse plants.
BAA comes in two types of formulations.
One is a water-soluble liquid concentrate that can be sprayed, applied with soil equipment, or added to irrigation.
The other type is a talc-based powder that is applied in a dry planter.
Here are some options:
BONIDE® Revitalize® Biofungicide with B. amyloliquefaciens
You can find Bonide Revitalize as a concentrate to mix with water or in spray-ready bottles available from Arbico Organics.
Monterey full disease control
Monterey Complete Disease Control is also available as a concentrate and ready to spray from Arbico Organics.
Arbico Organics supplies a number of products that contain BAA.
Another option is Arbor Biofungicide Concentrate, available in 16 ounce bottles from Gardener’s Supply Company.
These bacteria do not survive storage as long as other soil inoculants, and care should be taken when storing them as recommended on the label.
You will also have to reapply the bacteria every season. They do not cause long-term changes in the soil.
You can combine BAA with other soil inoculants. Trichoderma and arbuscular mycorrhizal fungi (AMF) can all co-exist with Bacillus amyloliquefaciens.
Naturally occurring Bacillus amyloliquefaciens offers many benefits
Bacillus amyloliquefaciens colonizes plant roots, putting it in a prime position to defeat pathogens for growth on the plant.
These bacteria fertilize the plant by supplying nutrients that are in short supply and producing chemicals that help the plant grow. They also prompt the plant to activate its own defense mechanism, keeping even more pathogens under control.
This strain of Bacillus also outcompetes other microbes in the soil and can inhibit both bacteria and fungi.
Have you used BAA to prevent disease in your garden? If so, let us know in the comments how it worked.
And read on for information on other biofungicides and biopesticides, including:
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