What Is A Biofungicide: Information On Using Biofungicides In Gardens

By: Amy Grant

Plants can be susceptible to a variety of pathogens, and just like a cold in a school group of children, be rapidly passed, potentially infecting an entire crop. A newer method for controlling disease amidst greenhouse and other commercial crops is called soil biofungicide. What is a biofungicide and how do biofungicides work?

What is a Biofungicide?

A biofungicide is made up of beneficial fungi and bacteria that colonize and assail plant pathogens, thereby thwarting the diseases they cause. These microorganisms are commonly and naturally found in soil, making them an environmentally friendly alternative to chemical fungicides. Additionally, using biofungicides in gardens as an incorporated disease management program reduces the risk of pathogens becoming resistant to chemical fungicides.

How Do Biofungicides Work?

Biofungicides control other microorganisms in the four following ways:

  • Through direct competition, biofungicides grow a defensive barrier around the root system, or rhizosphere, thereby shielding the roots from harmful attacking fungi.
  • Biofungicides also produce a chemical similar to an antibiotic, which is toxic to the invading pathogen. This process is called antibiosis.
  • Additionally, biofungicides attack and feed on the harmful pathogen. The biofungicide has to be in the rhizosphere either before or at the same time as the pathogen. Predation by the biofungicide will not affect the harmful pathogen if introduces after it has infected the roots.
  • Lastly, introducing a biofungicide kickstarts the plant’s own immune defense mechanisms, enabling it to successfully fight off the invading harmful pathogen.

When to Use a Biofungicide

It is important to know when to use a biofungicide. As explained above, introduction of a biofungicide will not “cure” an already infected plant. When using biofungicides in the garden, they must be applied before the onset of disease development. Early application protects the roots against attacking fungi and encourages vigorous development of root hairs. Biofungicides should always be used in conjunction with the basic cultural control of sanitation, which is the first line of defense for protection from disease.

Like any fungicide, the use of biological fungicide products should be applied according to the manufacturer’s instructions. Most biofungicides can be used by organic growers, are generally safer than chemical fungicides, and can be used in conjunction with fertilizers, rooting compounds, and insecticides.

Biofungicides have a shorter shelf life than their chemical counterparts and are not a cure-all for infected plants but rather a naturally occurring method for controlling disease prior to infection.

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Fight plant pathogens with the biofungicide Bacillus subtilis

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Bacillus subtilis is a type of bacteria that can survive in the soil for a long time. Many strains are highly effective in colonizing plant roots and fighting plant pathogens.

They can work directly against other microbes by producing a variety of antibiotics that infect fungi or bacteria. They can also act indirectly by stimulating the plant to activate its own defense mechanisms so that it can ward off attacking microbes.

This combination of activities results in a powerful bio-control agent that is commercially available to inhibit a number of pathogens in many different cultures.

Even better – in addition to its bio-control activities B. subtilis helps the plants grow more effectively.

At Gardener & # 39 s Path we explain in detail how these bacteria work and how you can use them in your garden.

REGALIA ® advanced biofungicides activate a plant’s natural defenses to protect against a variety of fungal and bacterial diseases, resulting in higher quality AND yields. REGALIA ® products are active against both soilborne and foliar pathogens, delay the development of resistance, and help minimize chemical residues. They can be used as stand-alone products or in combination with other fungicides to strengthen integrated pest management programs (IPM) and to help manage resistance in a wide range of organic and conventional crops, as well as in turf and ornamentals.

Complex and Unique Mode of Action

REGALIA ® biofungicides have a unique and complex mode of action, referred to as Induced Systemic Resistance (ISR), and carry a FRAC code of P5. ISR creates a defense response in the treated plants and stimulates additional biochemical pathways that strengthen the plant structure and act against the pathogen.

When applied to crops, REGALIA ® products activate ISR and induce the plants to produce specialized proteins and other compounds—phytoalexins, cell strengtheners, antioxidants, phenolics, and PR proteins—which are known to inhibit fungal and bacterial diseases and also improve plant health and vigor.

Key Benefits & Features

Ideal tool to strengthen existing IPM and IRM programs

* Protection against a wide range of foliar and soil-borne pathogens
* Improves overall plant health which can translate into a yield increase, enhanced root development, and plant vigor
* Complex mode of action (ISR), Group P5
* Mainstream performance

Helps simplify labor scheduling and avoids costly downtime

* 4-hour REI
* Minimal personal protective equipment (PPE) requirements

Can be used up to the day of harvest without concern for residues

0-day PHI
MRL tolerance exemption

Convenient to use

Easy-to-use liquid formulation
No spray buffer required

Provides maximum operational flexibility

OMRI approved and NOP compliant
Approved for field and greenhouse applications
Apply by ground, air, or chemigation

Biocontrol Bytes

Winter squash in our cucurbit powdery mildew biopesticide trial conducted in western NY, eastern NY, and on Long Island in 2018. We are also testing biopesticides for white mold. Photo credit: Meg McGrath.

Remember from Part 1 of this post that we (I and many great colleagues) are studying what biopesticides can add to effective disease management of cucurbit powdery mildew and white mold. After “what is a biopesticide?” the next most common questions about this project are about the specific biopesticides we’re testing:

  • How do they work?
  • Can I tank mix them with other pesticides or with fertilizers?
  • Do I need to use these products differently than I would use a chemical pesticide?

Today’s post will try to answer those questions.

Modes of action – How do they work?

As you may recall from February’s post, biopesticides work in different ways, and the five biofungicides we’re studying cover the range of these modes of action.

Biopesticides protect plants from diseases in different ways. I like to divide them up into the five modes of action (MOAs) in this table. Like many biopesticides, some of the products we are testing have more than one MOA. Click on the table to enlarge it.

Eats pathogen

The fungus active ingredient of Contans (Paraconiothyrium minitans strain CON/M/91-08 formerly called Coniothyrium minitans) “eats” (parasitizes and degrades) the tough sclerotia of the fungus, Sclerotinia sclerotiorum that causes white mold. Sclerotia survive in the soil from year to year. However, for this strategy to be effective, the fungal spores within Contans have to first make contact with the sclerotia. The time between colonization and degradation of sclerotia is about 90 days.

Makes antimicrobial compounds

The active ingredients in Serifel and Double Nickel are bacteria – same species but different strains. They both produce compounds that are harmful to plant pathogens (antimicrobial). According to the manufacturer, most of the foliar efficacy of Double Nickel is due to the antimicrobial compounds already present in the container. But the manufacturer notes that some of the efficacy also comes from the live bacteria that are responsible for this product’s other modes of action, especially the induction of plant resistance (more on this later). The strain of bacteria in Serifel has been formulated so that it contains only living bacteria (no antimicrobial compounds). The manufacturer’s goal is for the bacteria to produce antimicrobial products unique to the specific environmental conditions after application. Double Nickel and Serifel are examples of different strategies for using antimicrobial-producing bacteria to fight plant diseases. Our goal is to explain how the products work not tell you which strategy is better.

Some biopesticides contain microbes that grow on the plant. These beneficial microbes use up space and nutrients so there is no room for the pathogen, excluding it.

Excludes pathogen

The bacteria in Double Nickel and Serifel also can protect plants from disease by growing over (colonizing) the plant so that there is no space or nutrients available for pathogens. How important this mode of action is to the efficacy of Double Nickel depends on the setting and time of year (according to the manufacturer). Cucurbit leaves exposed to sun, heat, and dry air are not great places for bacteria to grow, and pathogen exclusion is not likely to be very important in protecting cucurbit leaves from powdery mildew. The antimicrobial MOA is more important here. Apple blossoms being protected from fire blight in the early spring could be a different story. The bacteria in Serifel tolerate a wide range of temperatures in the field, but the manufacturer recommends applying this product with a silicon surfactant to help the bacteria spread across the plant surface better.

Induces plant resistance

Plants have mechanisms to defend themselves. Some pathogens succeed in causing disease when they avoid triggering these defenses, or when they infect the plant before it has a chance to activate these defenses. Some biofungicides work by triggering plants to “turn on” their defense mechanisms. This is called “inducing plant resistance.” It is the sole mode of action of the bacteria in LifeGard, and one of the modes of action for the active ingredients in Double Nickel, Regalia, and Serifel.

Promotes plant growth and/or stress tolerance

The last biofungicide being studied in this trial has a plant extract as an active ingredient, instead of a microorganism. Regalia works by both inducing plant resistance, and also promoting plant growth and stress tolerance. Some of the other products in this trial also share these MOAs. According to the label, some crops treated with Regalia produce more chlorophyll or contain more soluble protein. This final MOA (promotion of plant growth and stress tolerance) is also sometimes shared with “biostimulants”. But remember that “biostimulant” is not currently a term regulated by the EPA. This may be changing in the future, so stay tuned. Biostimulants enhance plant health and quality. They are not registered as pesticides, and must not be applied for the purpose of controlling disease. Make sure you read and follow the label of any product you apply.

Best practices – How do I use them?

We’ll get to some product-specific details in a minute, but first some notes about best uses for all five of these products.

  • They need to be used preventatively. For biofungicides to eat pathogens, exclude them from plants, induce plant resistance, or improve plant growth and stress tolerance, they need to beat the pathogen to the plant. It takes time for the plant to fully activate its defenses, even if “flipping the switch” to turn those defenses on happens quickly. The same applies to promoting plant growth and stress tolerance. And if you want the beneficial microorganism to already be growing where the pathogen might land, of course you need to apply the product before the pathogen is present. Microbes that produce antimicrobial compounds also work best if they are applied when disease levels are low.
  • Use IPM. These biofungicides (and most, if not all, biofungicides) were designed to be used with other pest management strategies like good cultural practices, host resistance, and other pesticides. For example, they can be included in a conventional spray program to manage pesticide resistance.
  • Mix what you need, when you need it. Don’t mix biofungicides and then leave them in the spray tank overnight. Some products may need to be used even more promptly. Check the label.
  • Store carefully. Generally, away from direct sunlight and high heat. Follow the storage instructions on the label.
  • They have short intervals, but still require PPE. One of the benefits of biofungicides is short pre-harvest intervals (PHIs) and re-entry intervals (REIs). All five of the products we’re studying have a 0 day PHI and a 4 hour REI. But they all still require personal protective equipment (PPE) when handling and applying them. Read and follow those labels!
  • Tank mixing best practices still apply. The table at the end of this post has details about biological compatibility of these products in tank mixes, as reported by the manufacturers. But just like other pesticides, you need to follow the label instructions for mixing. If you have questions about a specific tank mix partner, confirm compatibility with a company rep. Do a “jar test” if you are mixing two products for the first time and want to know if they are physically compatible.

Biopesticides (especially those that contain living microorganisms) often need to be handled and used differently than chemical pesticides. They may be more sensitive to temperature, moisture, or UV light, which may impact the best time or place to apply them. And of course you don’t want to tank mix a living microorganism with something that will kill the good microbe. (Cleaning your tank well between sprays is always recommended, whether or not you are using a biopesticide.) The following table summarizes details for the five products we’re studying provided by the manufacturers – from product labels, company websites, and conversations with company reps. We have not personally tested this information.

Exactly how should you use these biofungicides to maximize their efficacy? This table summarizes best practices (as reported by the manufacturers) for each of the five fungicides tested in this trial. Click on the table to enlarge it.

We’ve created handouts that summarize the designs of both the cucurbit powdery mildew and the white mold trials, the modes of action of the five biofungicides we’re testing, and the best practices information presented above.

Stay tuned for Part 3 of this post – results from our first year of field trials!

This post was written by Amara Dunn (NYS IPM) and Sarah Pethybridge (Plant Pathology & Plant-Microbe Biology, School of Integrative Plant Science, Cornell University). Thank you to the New York Farm Viability Institute for funding.

Biocontrol Bytes

This summer we compared three biofungicides added to a conventional cucurbit powdery mildew management program in field trials conducted in western and eastern NY and on Long Island. Photo credit: Caitlin Vore, Cornell Vegetable Program

What we’re doing

This summer I have been working with great colleagues (Elizabeth Buck, Dr. Julie Kikkert, Dr. Margaret McGrath, Jud Reid, and Crystal Stewart) on a project funded by the New York Farm Viability Institute looking at the use of biofungicides (Remember what biofungicides are?) in vegetable disease management. Dr. Darcy Telenko (formerly of the Cornell Vegetable Program) helped plan the project before starting her new position at Purdue University, and Dr. Sarah Pethybridge has provided valuable advice based on her extensive work with white mold (including control with biofungicides). BASF, Bayer, BioWorks, Certis, Dow, and Marrone BioInnovations provided product for the field trials.

The project has two goals:

  1. Quantify what biofungicides add to management of cucurbit powdery mildew and white mold in terms of…
    – disease control
    – yield
    – plant health
    – economic value (comparing yield gains to fungicide costs)
  2. Evaluate the utility of NDVI (normalized difference vegetation index) as a measure of plant health and disease detection in fresh vegetables

Why this project?

For both diseases (cucurbit powdery mildew and white mold), we’re considering biofungicides used with other pest management – other biofungicides, conventional chemical fungicides, and/or cultural practices. Biofungicides are not expected to be silver bullets, and they work best when used in an IPM strategy. But when deciding whether or how to use them in your operation, it’s good to know what value you’re getting for the extra costs of purchasing and applying the products. This summer we ran trials in three major vegetable-producing regions of the state: western New York, eastern NY, and on Long Island.

Biofungicides for cucurbit powdery mildew

Cucurbit powdery mildew looks like a dusting of powdered sugar on the cucurbit leaf. These powdery spots start on the underside of the leaf, and then develop on the upper surface of the leaf, so excellent spray coverage is important. Photo credit: Amara Dunn, NYS IPM

For combatting cucurbit powdery mildew, we’re comparing three biofungicides: LifeGard (Bacillus mycoides isolate J), Regalia (extract from the giant knotweed plant Reynoutria sachalinensis), and Serifel (Bacillus amyloliquefaciens MBI 600). All three were applied weekly starting when the plants were small. Then, when the first signs of powdery mildew showed up, we started a rotation of conventional fungicides (Vivando, Quintec, and Luna Experience). These three treatments plus a rotation of all-organic fungicides (LifeGard, MilStop, Serifel, and a mineral oil) are being compared to two control treatments: the conventional fungicides alone, and plants that received no treatment for powdery mildew. We ran the trials on a variety of bushing acorn squash (‘Honey Bear’) that has intermediate resistance to powdery mildew.

Biofungicides for white mold

Most vegetable crops are susceptible to white mold, with legumes being among the most vulnerable. The name comes from the dense white “tufts” that the fungus forms. These develop into dark, hard sclerotia that can survive for years in the soil. Photo credit: Amara Dunn, NYS IPM

In the white mold trial, we’re looking at Double Nickel (Bacillus amyloliquefaciens strain D747) alone or in combination with Contans (Paraconiothyrium minitans strain CON/M/91-08 formerly Coniothyrium minitans). Next year we’ll look at these biofungicides in combination with reduced tillage at one site. Reduced tillage is another IPM strategy for white mold. The active ingredient in Contans is a fungus that eats the resting structures (sclerotia) of the fungus that causes the disease white mold. Because of this, it needs time to work, and is applied either in fall or spring. The goal is to reduce the number of sclerotia present in the next crop. Next year we’ll collect data on whether application of Contans reduced disease. In the meantime, during the 2018 growing season treatments we tested were Double Nickel, Cueva (an OMRI-approved copper) and no treatment for white mold on snap bean. Previous research by the EVADE Lab at Cornell AgriTech at The New York State Agricultural Experiment Station, Geneva, New York, has shown that Double Nickel is a promising biofungicide for white mold.

What is NDVI, anyway?

In a nutshell, the “normalized difference vegetation index” (NDVI) is a way to quantify how much healthy, green foliage is present. The device we used emits different types (wavelengths) of light (red and near infrared), and measures how much of each type of light is reflected back from the leaves of the plant. Leaves that are dark green and healthy reflect more infrared light and absorb a lot of red light. Less healthy leaves reflect less infrared light. A NDVI value closer to 1 indicates healthier plants. A NDVI value closer to 0 indicates less healthy plants (or more bare ground).

NDVI (normalized difference vegetation index) quantifies the amount of dark green foliage based on how much light of different wavelengths is reflected. It is used in some crops to decide when to apply fertilizer, or to help detect below-ground pests. Photo credit: Amara Dunn, NYS IPM

NDVI and similar indices are already used in other crops and in other places to help growers make decisions about when to fertilize, or to help detect parts of a field where a pest may be present. So far in NY, NDVI is not being widely used by fresh market vegetable growers for disease detection. Collecting NDVI data from this project will do two things:

  1. Help us quantify the health of plants. Even though NDVI is not a measure of disease, we would expect to see more healthy foliage if biofungicides are contributing to disease control.
  2. Provide some preliminary data to help us determine whether NDVI measurements could be useful to NY fresh vegetable growers.
Growers and industry reps had a chance to visit the 2018 cucurbit powdery mildew field trials shortly before they were harvested. Photo credit: Amara Dunn, NYS IPM

Field meetings were held at each powdery mildew trial location so that local growers could see the trials and hear about the project. We’re currently wrapping up data analysis from the 2018 field season. You’ll be able to learn about results from the first year of this two-year project at winter meetings around NY, in extension newsletters, and here on this blog. Also, stay tuned for Part 2 of this post with details about how these biofungicides work (modes of action), and how to use them most effectively.

This post was written by Amara Dunn (NYS IPM), Sarah Pethybridge (Plant Pathology & Plant-Microbe Biology, School of Integrative Plant Science, Cornell University), and Darcy Telenko (Department of Botany & Plant Pathology, Purdue University).

More Methods

Steaming soil cooks Verticillium mycelia, but solarizing with a big sheet of black plastic might be the practical choice for an urban garden plot. Rotating resistant plants such as carrots (Daucus carota) or beans (Phaseolus spp.) for five years or more in affected areas may deny food to the fungus. With enough land, you might try the “nuclear option” -- let the land lie fallow and plant cover crops such as annual rye grass, using the “green manure” they produce to keep microbes healthy and chomping on fungus -- then plant only resistant species or plants with a “(V)” after the name to indicate resistance.

About Soil Biofungicide - How Do Biofungicides Work For Plants - garden

[From the April 2014 issue of the UC IPM Green Bulletin newsletter]

The term biofungicide can have several different meanings, but it is most frequently used to refer to fungicides that contain a microorganism (usually a bacterium or fungus) as the active ingredient.

Advances in fermentation technology have allowed mass production of highly specialized microbes that previously could only be grown in small batches on highly specific substrates, such as on roots infected with pathogens. Consumer demand for organically certifiable pesticides and increased regulatory pressure on older synthetic pesticides, especially in Europe, has

Since microbial biofungicides contain living organisms, their modes of action differ from those of synthetic fungicides. Some of these mechanisms include:

  • Competition: The biocontrol agent is more effective than the pathogen at gathering critical nutrients or space and, therefore, must be in place before disease onset.
  • Antibiosis: The biocontrol agent produces a chemical compound of some type (antibiotic or toxin) that acts against the pathogen.
  • Predation or parasitism: The biocontrol agent directly attacks the pathogen.
  • Induction of host plant resistance: The biocontrol agent triggers a defensive response in the host plant that limits the ability of the pathogen to invade the plant.

Most biofungicides use one or more of the above mechanisms to target only one or a few specific pests. As such, applicators should both read the label and diagnose the problem carefully to insure that the product will be effective. Biofungicides work best when applied preventively. Application after a plant is already infected has little chance of significantly altering the course of the disease for that plant, although it may decrease the ability of the pathogen to move from that plant to other plants, especially if the pathogen has to move through the soil to do so. Thus, an application of biofungicide is not likely to cure an infected plant but it may protect other nearby plants in the field.

Biofungicides cannot take the place of proper cultural care. They are a valuable tool for keeping a strong plant healthy, but they cannot forestall the inevitable. If your client's Japanese maples are routinely drowned, allowed to wilt, and then drowned again, adding a biofungicide will not prevent them from contracting Phytophthora if it is present in the soil.

If biofungicides are a useful and environmentally friendly tool in the landscape, why aren't they more widely used? One reason is that these fungicides rely on living organisms for efficacy, so they must be stored appropriately in order to retain their fungicidal properties over time. However, a more commonly cited reason is that the personal protective equipment needed to apply them is more involved than for some other compounds. Routine exposure to the proteins found in the spray mists of some biofungicides can result in the development of allergic reactions. To keep commercial applicators safe, they must wear NIOSH approved respirators when mixing, loading, or applying biofungicides in agricultural or landscape settings. This may not be immediately obvious when reading the labels, as a quick scan often only shows the following required personal protective equipment (PPE):

  • Long sleeved shirt and long pants
  • Shoes plus socks
  • Waterproof gloves

The respirator requirement is only evident when reading the text following the list. Biofungicides are safe to use as long as mixer/loaders and applicators have and use a respirator as part of their PPE. However, a NIOSH approved respirator requires proper training and fitting in order to be effective.

When used properly and with forethought, biofungicides can be an important part of an IPM program to prevent or mitigate problems with plant pathogens in the landscape. However, nothing can ultimately take the place of proper plant selection and care.

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