Use of biological additives, also called ‘active ingredients’, for the suppression of pathogens and insects provides growers with an option in their integrated pest management toolbox. Some are applied above soil line to reduce plant diseases or reduce insect pests. Others can be introduced to the root zone or blended into growing media to enhance plant growth and/or to reduce the incidence of plant root diseases. Questions are often asked: “How effective are active ingredients?” “Can active ingredients replace chemical treatments?” “Can they be used in combination with chemical treatments?” and “Are they cost effective to provide a return on investment?”. Because there are many types and uses, let’s focus on the use of active ingredients for the plant root zone.
Why Convert to Active Ingredients?
A main advantage of using active ingredients is that they are safer to use than chemical pesticides and they have little to no toxicity to plants, humans or animals. Most have been discovered in mineral soil, are naturally occurring and not genetically modified. Because they are part of the normal checks and balances of soil biology, there is less potential for pathogen resistance.
Most active ingredients that suppress pathogens or insects are preventative, not curative; therefore, they minimize the onset of plant diseases before they have a chance to affect crops. Pathogenic fungi and other natural occurring fungi found in soil and growing media are often a food source for insects, particularly fungus gnats. The benefit of reducing root pathogens also has a secondary benefit of reducing fungus gnats, which are often vectors for plant pathogens. Most beneficial active ingredients remain in the root zone of the plant for an extended period, while some can remain with the plant for life. If you are growing certified organic crops, a major advantage is that most active ingredients are certified or listed for organic crop production. This is a great option to where chemicals cannot be used.
Living Organisms – Handle with Care
Active ingredients are living organisms and may require special storage and use conditions. Almost all active ingredients have a shelf-life for their optimal use, so users need to respect the expiration date. Since fungal organisms are sensitive to warmer temperatures and may require cool storage temperatures. Fungal organisms may also desiccate easily, therefore reducing their effectiveness.
Bacteria are more robust and forgiving when handling, storing and applying due to the thick cell walls of their spores. When incorporated into growing media, active ingredients work best when growing medium temperatures are above 10°C (50°F). Unlike chemical fungicides that are wide spectrum, biological controls generally interact with specific pathogens, therefore their range of pathogen suppression can be narrower that their chemical counterparts. If used in combination with chemical controls or other biological additives, be sure to check the compatibility of the microorganism with the chemistry and other bioadditives used. Most fertilizers and pesticides are compatible and safe to use with active ingredients, except for the obvious, such as bactericides, some fungicides and sanitizers. Some chemicals and other active ingredients may reduce populations, while others may eliminate the beneficial microbes.
This is a microscopic picture of bacteria (Bacillus pumilus PTB180) growing along the hyphal structures of endomycorrhizal fungi (Glomus intraradices PTB297). The bacteria absorb carbon from the mycorrhizae hyphal network and multiply to produce a biofilm composed of lipopeptides and/or hormones. These beneficial active ingredients work together to form a network with plant roots to suppress certain root pathogens and supply roots with water and nutrients to enhance plant growth. Source: Premier Tech
Biocontrol and Biostimulant: What Makes Them Difference?
Scientists have worked and studied beneficial microbes for use in plant culture, whether for field applications or for greenhouse, controlled environments. Beneficial microbes have been isolated, cultured and produced in laboratories to be sure that strains remain true and continue to provide the desired benefits. If we review the various microbes commercially available, we can place them into two general categories by the benefits they provide: biocontrol or biostimulant. Biocontrols are active ingredients that reduce the incidence of plant diseases and/or insects. They may directly attack the pathogen or insect, or indirectly control by creating a barrier, produce a metabolite or block a food source. Biostimulants stimulate plant growth or assist plants in acquiring nutrients and/or water to improve the overall growth of plants.
Value-Added Growing Media That Suppress Root Diseases and Certain Insects
More than 8 years ago, Premier Tech released PRO-MIX® growing media products with BIOFUNGICIDETM and MYCORRHIZAETM active ingredients. These products contain two unique, compatible active ingredients. BIOFUNGICIDETM, which is a bacterium, Bacillus pumilus PTB180, suppresses certain fungal root pathogens, including Alternaria, Fusarium, Pythium and Rhizoctonia. MYCORRHIZAETM is a natural isolate of mycorrhizal fungi, Glomus intraradices PTB297, that is known to be a strong colonizer that benefits overall growth of plants and is compatible with a wide array of plants species.
Pansy, three plugs per 4” pot 8 weeks after transplanting. Those with Bacillus pumilus and mycorrhizal fungi on the right are larger and healthier than the untreated on the left. Source: Premier Tech
Interestingly, early research work in the 1990s suggested that some types of Bacillus bacteria could suppress certain soil insects. Pioneering laboratory work from Kuhne & Heller1 mentioned that fungus gnats do not lay their eggs randomly on moist surface of growing media. They preferably lay their eggs on hyphae of certain phytopathogenic fungi (Botrytis cinerea, Fusarium species and Phoma betae) on which their larvae feed, rather than on other fungi or bacteria (B. pumilus). Their research suggested that there could be an indirect effect of lowering insect populations by reducing the fungal food sources.
Further work at Premier Tech, and in conjunction with Laval University, demonstrated that Bacillus pumilus PTB180 bacterium has an indirect suppressive effect on certain insect populations, particularly fungus gnats and thrips. Further, research found that PRO-MIX® growing media containing Bacillus pumilus PTB180 suppress both fungus gnats and thrips, to an average level of 30% and 22% respectively during the crop cycle. These findings were submitted to the EPA and PRO-MIX® BIOFUNGICDETM+MYCORRHIZAETM was labelled for indirect suppression of fungus gnats and thrips in 2019.
Premier Tech is conducting additional research trials with active ingredients to investigate the potential to suppress other pathogens and insect pests. The major advantage of having active ingredients in growing media prior to planting is that these microbes are present in the root zone before root diseases have a chance to get established. Also, the best value and return on investment is to have the active ingredient added to the growing medium for you, since the cost of the product is often less from the manufacturer, and you do not have added labor costs to apply it.
Reference: Kuhne Heller. 2010. “Sciarid fly Larvae in Growing Media …” Proceedings of the International Peat Symposium Peat in Horticulture – Life in Growing Media – Amsterdam, 11 October 2010 pp. 95-102