How to Optimize the Performance of Microbial Fungicides

By Griffin Greenhouse Supplies|February 6, 2024

Botrytis in Begonia microbial fungicides

Botrytis spreading within the begonia canopy attacking senesced blooms, foliage, and stems. Photo: Griffin

Growers looking for an advantage in the fight against plant pathogens are adding microbial fungicides to their disease management strategies. Microbial fungicides, or biofungicides, are a class of fungicides where the active ingredient is a microorganism or a microorganism’s byproduct, derived from fungi, bacteria, or plants. Microbials prevent the spread of plant pathogens using multiple modes of action (MOA), including competitive exclusion, predation, antagonistic metabolites, nutrient competition, and induced resistance in the plant host.

Commercially available microbial fungicides employ two or more of these modes of action, reducing the possibility that pathogens can develop pesticide resistance. The MOA are officially (FRAC) classified as “NC”, or not classified due to the various pathways they may take.

There are many advantages to using microbial products, including short reentry intervals, short pre-harvest intervals, and good plant safety. Because these microorganisms colonize, protect, and stimulate the natural defenses in the host plant, they promote better plant health. Healthier plants are more stress- and drought-tolerant. Additionally, they are typically certified for organic production and labeled for a wide variety of edible species.

However, microbials work slowly, and it takes time to realize the full benefit of their use. Microbial fungicides must be applied prior to the onset of disease. They are not an effective rescue treatment for plants that are already infected and damaged by pathogens. Use them preventatively and monitor for the early onset of disease symptoms. Do not hesitate to use a conventional fungicide option to correct an issue before applying a biofungicide for ongoing prevention.