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Microbial Inoculants: Fighting Mission Impossible

Microbial InoculantsYour mission, if you choose to accept it, is to incorporate sustainable practices into your growing operation. While not life-threatening, many still believe this mission to be impossible. Research funded by AFE is here to prove otherwise.


Microbial Inoculants (MI’s) are agricultural amendments that use beneficial bacteria and/or fungi to promote plant health. Sometimes by forming symbiotic relationships with host plants and other times by using up all excess nutrients, MI can prevent a wide range of soil-borne pathogens that cause serious crop loss.
MI’s are a widely marketed form of biocontrol, with more than 80 commercially available products, and are considered much more environmentally friendly than traditional fungicides. But growers have always wondered if they actually work.
Research Results
Late last year, Dr. George Elliott, Dr. Wade Elmer and Dr. Susanne Bodmann completed AFE-funded research evaluating the effectiveness of various commercially available MI’s in controlling pythium and blackleg disease of seed geranium in soil-less potting mix. While not one of the stated objectives, a finding of high-disease control could support more sustainable growing practices by allowing decreased use of fungicides.
Unfortunately, the results of this three-year, multi-part study were inconclusive. According to Dr. Elliott, some experiments showed control as good as standard chemical treatments; other experiments showed no control at all. Additionally the factors controlling effectiveness seem hard to pinpoint. What worked in one trial didn’t in the next, even with all inputs the same.
Dr. Elliott hypothesized that the disparity could come from inconsistencies in the potting media (no two samples are exactly the same) or from uncontrollable contaminations in the greenhouse, either by people or insects.
“Microbial Inoculants definitely do not suppress disease once it has started,” said Dr. Elliott, “but they might prevent it.”


So if the results were inconclusive, how can growers put this research to use? One thing Dr. Elliott advises growers is to focus on sanitation: Start with a good growing mix that contains adequate aeration and ensure an environment not conducive to disease by controlling moisture levels.
Second, growers should conduct their own trials to evaluate the effectiveness of MI’s in their individual situation. These trials should include both plants inoculated with MI’s and those grown without it, ideally in the presence of the disease pathogen. Additionally, Dr. Elliott recommends repeating the trial on a regular basis to ensure continued effectiveness.
While not a miracle cure, MI’s can be an effective biocontrol for certain soil-bourne diseases. The key to using them, and this AFE-funded research, is determining for yourself how products like this can be used under your unique growing conditions and within a complete disease-prevention program that includes proper sanitation, high-quality inputs and regular trialing.