By Carol Miller, Editor, American Vegetable Grower
As growers strive to find ways to make their crops resilient to climate shifts and increasingly significant abiotic stressors, one valuable tool available to them is biostimulants.
Not only are these products made up of naturally occurring components, they help plants endure stress from drought to temperature to soil conditions. Stressed plants require more inputs to reach a desirable yield, which in turn turns up the pressure on the environment through increased nitrogen use and greenhouse-gas-producing manufacturing and shipping methods. Conversely, stressed plants are less likely to be able to endure late frosts, intense storms, or droughts that growers now deal with on a more regular basis.
We spoke with one of the leading experts in biologicals, Dr. Patrick Brown, Distinguished Professor, University of California, Davis. He has a slew of awards and honors, including Chairman of the International Congress for Biostimulants. Brown talked about some promising developments in biostimulants as well as an existing regulatory challenge we need to overcome.
Miller: How are biostimulant manufacturers using these products to help address environmental stresses?
Brown: A lot of biologicals companies have been targeting specific ‘stress points’ in the agronomic cycle. Challenges like temperature stress at seeding if the soil is too cold or the soil is too wet. Products that improve cold tolerance and increase the speed of root extension into the soil would be valuable and a number the biostimulants have this target.
Also, as you get a little closer to flowering, heat stress, wind stress, and drought stress also cause the plant to lose productivity, reduce your corn seed set, et cetera. And there are a number of companies that have been targeting that particular aspect of the growth cycle.
So, we have been seeing a lot more focus in the industry and attempts to design products around agronomic needs. Ideally, these products get a plant through the existing climate event. There's a small group of the very best of these products that do that.
And I think we're going to see more of that because a lot of the biostimulant companies have now been purchased by the major players. I think they're going to bring to bear all of their technical expertise to optimize these [products].
Technology a Key Factor in Biostimulant Success
Miller: How important is timing with biostimulants and how can growers know when a field, greenhouse, or orchard is ready for treatment?
Brown: Almost all of these products are designed to mitigate a stress and will only have value when applied prior to the stress.
So, you need to have good systems to predict whether the stress event is going to happen, be it next week, in 2 weeks, or 3 weeks. That need for accuracy is going to be constraining.
Now obviously we have good weather forecasting capability. But I think we need to go to a higher level of precision in that regard. And a higher level of specificity down to a particular farm and event.
To be truly effective, biologicals must be coordinated with improved precision meteorology and precision decision making in order to optimize their effect. You don't want to apply a product if the stress will never occur.
That level of precision is a challenge for multi-rotational vegetable crops like you'd see in the Salinas Valley of California. Production for those crops is very intense and time dependent. You have intense market demands for quality and for the timeliness of harvest.
And then of course, you've got all of those rotations. If you went from broccoli to lettuce, broccoli will leave two thirds of its nutrient in the soil through the stems that get turned under. I haven't seen a lot of the biostimulants/biofertilizers targeting the challenge of when will that residue breakdown and when will it be available to the new crop.
So that's going to be a difficult cropping system.
The PGR Regulatory Conundrum
A single EPA decision in the 1970s has resulted in the agricultural industry being leery of fully exploring how biostimulants work. Current EPA regulations consider anything that acts as a "plant growth regulator" (PGR) as a pesticide. This occurred because at that time, most products containing PGRs were indeed used as herbicides, Brown says.
Once PGRs gained that pesticide label, any product that regulates plant growth and uses that terminology is at risk of being deemed a pesticide — even if it enhances growth rather than limits it, and even if it's a naturally occurring substance.
Miller: How is that EPA decision still impacting biostimulants today?
Brown: Every event, every response that a plant has to its environment is mediated by plant growth regulators, by definition. So, when I water a plant that was droughted and it responds, that is a whole-plant growth regulatory response.
Go all the way back to Norman Borlaug and the Green Revolution, where he won the Nobel Prize for increasing the yield of maize and wheat and rice by 500%. He did it through traditional breeding, but when we go back and look, what actually did he do?
He modulated plant growth regulators. He changed natural gibberellin pathways with the resulting increase in productivity, saving an estimated 3 billion from starvation.
There is a discrete list of plant-produced plant growth regulators — auxin, ethylene, cytokinin, gibberellin, brassinosteroids, and strigolactone. Even today, if you spray something that contains a cytokinin, a known plant growth regulator, then it’s a pesticide.
Where the limitation has happened in the past is if you make a claim that says, “My product regulates the growth of the plant.” That could trigger a plant-growth-regulatory definition and hence trigger pesticide regulations.
So, a biostimulant company right now can say, “My product supports the ability of the plant to reach its full potential.” That would be an allowable claim, but. “My product regulates the growth of the plant so that it achieves its real potential.” No, no, no.
Even if a company had done all its due diligence and looked through the molecular biology of the plant, recognized a constraint that, if removed, would make the plant grow better, identified that constraint was an interaction with auxin or cytokinin, and then put that all in their literature… they would risk being regulated as a pesticide.
So, there's been this sort of absurd outcome that some companies are reticent to find out why their product works.
The other oddity which is worth mentioning is that seaweed has long been used as sort of a biostimulant. They've got a history of hundreds of years of being used. And more recently they have been commercialized.
Seaweed producers did their due diligence and analyzed all the constituents found in seaweed. They identified the presence of very low levels of some cytokinins and some gibberellins. They listed them and were subsequently classified as pesticides by virtue of that content.
This lack of clarity makes it difficult to publish and hence it constrains our discovery and hence limits product development. And that's the consequence of the regulatory constraints.
If I eat a bowl of spinach, I will get 10 times more plant growth regulator than I would if I ate a bowl of seaweed. Because it's a plant. Of course, it has those plant regulators in there.
To me this remains a very difficult thing to navigate. These products have their greatest promise as a mechanism to regulate plant growth in response to stress. It is a bit absurd that merely rearranging that sentence to read ‘plant growth regulation in the face of stress’ turns a product into a pesticide, even though the product is entirely safe. Limiting investigation into your product so you don’t trigger that label is clearly in no one’s benefit.
We have done some big studies ourselves, but we had to do it in a way that is less than ideal.
Very often, when as a university researcher you're researching these products, you won't be provided with a listing of the full chemical and molecular components of the product because of the producers’ fear that you might discover something that regulates the growth of plants — which is absurd, because that's your goal.
People don't want to go down the route of working out the molecular mode of action because of what it would trigger.
The industry has been limited by the regulations. There's no question.
