Golf course superintendents say biostimulants are expensive and, because there are so many on the market to choose from, they want to know which work best. They also want justification for using biostimulants, as well as evidence they work. If they have a neutral effect on turfgrass, then why should they be used? Those who don’t use them are wondering if they’re missing the boat.
Superintendents wanted these uncertainties cleared up, so about 85 attended a seminar at the GCSAA education conference during the Golf Industry Show presented by Keith Karnok, Ph.D., a University of Georgia professor. According to Karnok’s studies, 41 percent of golf course superintendents use biostimulants on a regular basis, 39 percent use them occasionally and 20 percent never use biostimulants. The bottom line is a majority of superintendents use biostimulants.
Biostimulants can be defined as anything that temporarily increases the activity of some vital process or organ. These enhancers can be applied to plants, soil or both. Biostimulants can improve rooting, turf quality and stress tolerance.
There are 60 active ingredients in biostimulants, with the four primary groups being hormones, carbon sources, humates and microbes. Hormone-based biostimulants include cytokinins, gibberellic acid, kelp extract, seaweed and sea kelp.
A plant hormone is an organic compound synthesized in one part of the plant and translocated to another part where, in very low concentrations, it causes a physiological response. There are five groups of hormones: auxin (produced in the shoots), gibberellins (produced in the roots), cytokinins (roots) and ethylene (entire plant). These hormones promote:
· Stem elongation;
· Adventitious rooting;
· Lateral root initiation;
· Leaf expansion;
· Seed germination;
· Stolon and tiller initiation;
· Translocation of carbohydrates and certain nutrients; and
· Transpiration.
Hormones also can inhibit root elongation, adventitious rooting, seed germination, stem elongation and cell division. What the hormone promotes or inhibits depends on the hormone level in the plant. The promotion of growth is realized when hormones are at naturally occurring or normal levels in the plant. There is an inhibition of growth when hormone levels are too high or at deficient levels in the plant.
Certain environmental and cultural stresses – such as draught, flooding, nutrient deficiencies, high and low temperatures, saline conditions and anaerobic conditions – can limit hormone production. Turf species and plant hormones can vary in their response to biostimulants. Sometimes they work, other times they don’t, Karnok says.
In most cases, turfgrass soils have an abundance of microbes and the benefits of adding mycorrhizae to turf soils haven’t been shown, Karnok says. Turfgrass soils usually have sufficient carbon for microbes because photosynthesis provides the necessary carbon for turfgrass growth. Good agronomic practices will ensure a healthy soil microbe population.
Making the purchase
Before buying a biostimulant, it’s recommended that superintendents request university test results, talk to peers to find out what works for them, do their own on-site testing and be wary of far reaching claims made by manufacturers.
When buying biostimulants, Karnok says superintendents are going on faith about the validity of the label because there are no quality checks like with seed productions and strict regulations like there are with pesticides, although biostimulants do have to meet Environmental Protection Agency regulations. Some are classified as fertilizer, but don’t want that classification because of the hoops that need to be jumped through.
In the end, hormonal-based biostimulants have great potential but more research is needed because a shotgun approach is currently being used, Karnok says. The greatest change for success is to apply biostimulants just before the onset of stress conditions.
There’s little scientific evidence that feeding microbes or turfgrass plants carbon sources is substantiating effectiveness. Humic substances have good potential in certain situations but more research is needed on turfgrass. The greatest chance for success when using them is on low organic matter and low fertility soils. Inoculating soil with microbes is doubtful at best, but there’s good potential using frequent applications, Karnok says.
The only way to justify biostimulants is with the cases in which superintendents say they work. There’s not enough research to justify them at this point, Karnok says.
