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Using Biofungicides

October 08, 2013

More and more growers are turning to softer chemistries and biofungicides to prevent and control various plant pathogens. Biofungicides, also known as biological fungicides, contain living organisms such as fungi, bacteria and actinomycetes which suppresses and/or controls the development of certain plant pathogens. Biofungicides are primarily marketed for controlling soil borne pathogens and improving root health. However, some of these products are also effective at preventing the establishment of certain foliar diseases.

Modes of Action
Since biofungicides contain living organisms, they control pathogens using very different modes of action than those of traditional fungicides. These products reduce disease development by using differing mechanisms such as antagonism, competition, antibiosis, enhanced nutrient uptake, and or by inducing host resistance. Biofungicides which suppress pathogens with several modes of action usually provide better control and are often effective on a wider range of target pathogens.

Many biological control agents  suppress disease development by competition; they essentially occupy the sites where pathogens usually enter the plant which prevents them from invading the tissue. Products using this method to suppress diseases must by applied before plant pathogens are present.

Antagonism occurs when the biological control agent attacks and feeds on the pathogen. This mode of action occurs infrequently and the biofungicide must be present before or just as the plant pathogen appears in order to provide effective results.  

The mode of action of antibiosis involves biological control agents which produce secondary metabolites or toxins which inhibit the germination and growth of the plant pathogen. This mechanism is primarily effective before an infection occurs; once the pathogen has gained entry inside the plant antibiosis is much less effective.

Some biofungicides have been shown to improve growth and suppress diseases by increasing the nutrient availability in the root zone. These biological control agents modify the media pH and/or increase the availability of certain elements through enzymatic activity. In many instances, plants treated with these biofungicides appear larger than untreated plants with or without the presence of a pathogen.

The last mode of action some biofungicides exhibit is the triggering of defense mechanisms within the treated plant. Certain biological control agents produce salicylic acid which triggers plants to activate their natural defense mechanisms rendering them less susceptible to infestations.

Controlling Soil Borne Plant Pathogens With Biofungicides
It is important for growers to understand that biofungicides work best when they are used preventatively rather than curatively. Therefore, it is best to apply biological control agents to the growing mix early in the production cycle before plant pathogens are present. Early applications allows time for the living organisms (microbes) to colonize, enabling them to out-compete or attack the pathogens once they do become present.

Biofungicides are commonly incorporated in to the growing mix prior to planting crops or applied through the irrigation water and drenched on after potting or during production. Depending on the type of biofungicide and the duration of the crop, it may be necessary to re-apply these products at various intervals during production to retain the disease suppression benefits.

In many instances, biofungicides can be used in conjunction with traditional fungicides to provide growers with greater disease control than when using either type of product alone. Many growers have observed equivalent, and in some cases, better disease suppression when using biofungicides in combination with reduced use rates of chemical fungicides compared with using either type of product alone. These synergistic results are possible when the beneficial organisms weaken the pathogenic fungi's cell walls rendering them more susceptible to chemical fungicides.

Grower interest and the use of biofungicides will likely continue to increase due to governmental regulations/restrictions of conventional fungicides, environmental concerns, and fear of resistance to existing products. Biofungicides usually provide great preventative control of soil borne plant pathogens and usually reduces the use of chemical fungicides. Biological control agents are generally safer to apply, have lower re-entry intervals, and are provide increased safety to crops compared with many of the traditional fungicides. Additionally, many biofungicides can be used in rotation or in combination with other fungicides, insecticides, and fertilizers. Always read product labels for application methods, rates, compatibilities and restrictions.

Having a general understanding of biofungicides, how they work, and what they can do will enable growers to better incorporate biological control agents into their production systems.  

Paul Pilon
Perennial Solutions Consulting

The mention of specific active ingredients does not constitute an endorsement or recommendation of, or discrimination against similar products not mentioned. ALWAYS READ PRODUCT LABELS AND USE THEM AS DIRECTED ON THE LABEL.


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