Sea? I told you it might help

 Editor's note: This post is the  “Verdure” column by Beth Guertal, Ph.D., published in the December 2014 issue of GCM. 

The use of seaweed (Ascophyllum nodosum Jol.) extracts (SWE) as a turfgrass treatment has been trotting around for a quite a few years now. One of the issues with the study of SWE, which are thought to impart stress tolerance, is that the commercial products are highly variable. It’s hard to track the actual active ingredient, especially when the SWE are part of a brew that also may contain iron, humic acids, wetting agents and vodka (OK, maybe not that last one).

Erik Ervin and his crew at Virginia Tech have long been unraveling the effects of this brew, and his work has recently focused on a key active ingredient in SWE – cytokinins. His work clearly showed that SWE contains biologically active levels of the proven heat-stress helper cytokinin. But what concentrations of cytokinin are needed to help a stressed turfgrass plant? In 2010, Dr. Ervin set out to determine the levels of cytokinin needed in SWE that would create a response in creeping bentgrass.

The work was done in a growth chamber, and L-93 creeping bentgrass was exposed to two temperature regimes: 95/77 F (35/25 C) (day/night) and 100/82 F (38/28 C) (day/night). The grass was treated with cytokinin from a seaweed source every two weeks, with four applications in all. The seaweed was applied to supply cytokinin at rates of 1, 10 and 100 uM. As a reference, the 10 uM rate equals 3.5 ounces per 1,000 square feet, applied in 1 gallon of water per 1,000 square feet. There was a comparison synthetic cytokinin treatment, too, which was applied at the same rate as the cytokinin in the seaweed extract. Collected data included turfgrass quality, leaf chlorophyll content and leaf measurement of cytokinin content (via trans-zeatin riboside).

The cytokinin treatments worked. As the bentgrass was exposed to heat stress, the color of the grass declined. However, the addition of any cytokinin improved turfgrass quality at the lower level of stress (95/77 F; 35/25 C). When it got really hot (100/82 F; 38/28 C) the 1 uM treatment of cytokinin from the seaweed was not effective, but every other cytokinin treatment still improved turf quality. The addition of any cytokinin also increased leaf chlorophyll content and, again, the higher rates (10 and 100 uM) were needed as heat increased. The cytokinin was measured in the leaf tissue, with significant increases in trans-zeatin riboside particularly found in the treatments receiving cytokinin at 10 and 100 uM. This was found at measurement intervals from 7 to 49 days after treatment.

In all, repeated application (four applications for this work) of cytokinin from seaweed and synthetic sources benefited creeping bentgrass growing in a stress situation. When the stress (heat) increased the two higher rates of cytokinin were needed, but the 10 uM dose worked as well as the 100 uM dose. A key note was that the materials needed to be applied before the onset of the stress, and thus they are a preventive, and not a curative, measure.

Source: Zhang, X., K. Wang and E.H. Ervin. 2010. Optimizing dosages of seaweed extract-based cytokinins and zeatin riboside for improving creeping bentgrass heat tolerance. Crop Science 50:316-320.

Beth Guertal, Ph.D., is a professor in the department of agronomy and soils at Auburn University in Auburn, Ala., and the incoming editor-in-chief for the American Society of Agronomy. She is a 17-year member of GCSAA.