A look at plant biostimulants

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The so-called miracle products promoted, sold and used in turf management are often referred to as “snake oil” or “foo-foo juice” (a sarcastic reference to the mythical foo-foo tree).

Some products make claims that are substantiated with scientific research in turfgrass systems, while many others lack direct evidence that they actually work within a turf management program.

The term “plant biostimulant” is often used to describe the various categories of substances used in these products: plant growth hormones (for example, auxins, abscisic acid, cytokinins, gibberellic acid), microorganisms (for example, Bacillus species, mycorrhizae, etc.), amino acids, humic and fulvic acids, plant defense-inducing substances, plant growth-promoting substances, vitamins, pigments and oils, soil amendments, soil conditioners, composts and compost teas, etc.

The EU’s take on plant biostimulants

Recently, the European Union has proposed policies and regulations to support and enforce what it calls a claims-based definition of plant biostimulants. In other words, plant biostimulant products should be defined by their function, not by the ingredients inside the container.

The EU also proposed that plant biostimulant products should be required to have credible demonstrated effects to support the product claims — that is, documented research to support product label statements for the crops and markets targeted.

For example, if product A contains a microorganism that, when applied to the soil, interacts with plant roots to induce a plant defense response to a plant pathogen, then the manufacturer must provide data supporting that claim for that particular crop and use. No longer would the manufacturer be able to state that “because the micro­organism has been shown to induce a plant defense response in peppers, go ahead and use it on putting greens.” The manufacturer would have to prove the biostimulant inside the product performs the function for that particular crop or use as stated on the label.

The European Biostimulant Industry Council (EBIC) has worked in partnership with government, academia and industry to co-develop guidelines for assembling the proper dataset that reflects consistent and reliable trial results. The guidelines contain two main points: Data must be generated to support the biostimulant claim, and that data must be used to place the product into the EU market and/or support commercial product claims. The data required will depend on the biostimulant’s claim.

Defining plant stimulants
The EBIC’s functional definition of plant biostimulants is as follows: “a material which contains substance(s) and/or microorganisms whose function, when applied to plants or the rhizosphere, is to stimulate natural processes to benefit nutrient uptake, nutrient efficiency, tolerance to abiotic stress, and/or crop quality, independently of its nutrient content.”

Why is there a functional definition of plant biostimulants? The EU’s position is that the purpose of biostimulants is to support ecology-based agricultural and food production systems. Take, for example, the last part of the definition: “to stimulate natural processes … independently of its nutrient content.” Although a biostimulant product may contain a fertilizer component (that is, nitrogen or iron), the observed demonstrated response of the plant is due to the biostimulant and not the fertilizer effect.

Hoop house rainout shelter
A hoop house rainout shelter is used for evaluating the efficacy of biostimulants in alleviating the effects of drought and heat stress.


For example, when plants are subjected to drought and/or heat stress, increases in clipping yield or chlorophyll content could not be achieved by the application of the minute amount of nutrients in the biostimulant product when these nutrients are applied alone as a positive check.

Research-based data
Regarding the required research-based data needed to support biostimulant claims, the EU has proposed guidelines and criteria for laboratory, greenhouse and growth chamber experiments that include the use of a 90% probability statistic and field trials, particularly field trials conducted under real-world conditions. Included in those guidelines are the number of trials (three) required under various environmental and geographic conditions, and the appropriate use of statistical analysis and data interpretation. Published, peer-reviewed scientific literature can be used to support a claim if it is of acceptable quality under those EU guidelines.

Considering biostimulants: Advice for golf course superintendents

Should the U.S. Department of Agriculture adopt the EU’s claims-based definition of biostimulants for use in the United States? If so, what does that mean for our industry? Moreover, what do golf course superintendents think about a claims-based definition of biostimulants?

What are the key questions superintendents should ask when considering a plant biostimulant product?

  • What’s in it?
  • What is its function? How does the product claim to benefit turf?
  • Will the product function in all climates, soil types, turf species and stress conditions?
  • Does the product function best to help with abiotic (drought, heat, salt) or biotic (insects, pathogens, traffic) stresses?
  • Where’s the data? What does the data show that the product does when the product is applied to turf? Were the effects both qualitative and quantitative in replicated field trials?
  • Does the manufacturer have clear data showing that all or most of the product’s ingredients are essential to its function? Does the data show how individual ingredients, when tested against the formulated product, no longer provide the functional benefit?

Currently in the U.S., most biostimulants are sold as components in fertilizer formulations or as soil amendments. Would development of clear definitions and guidelines for biostimulant products benefit the turf industry? Let’s assume a new product appears in the market. A good first question to ask would be whether the product has been appropriately developed.

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