10/3/2023 - By Dr. Raymond Snyder

The beginning of Autumn signals a changing of the seasons and is a nice break from Summer’s hot temperatures. This change of season also results in a noticeable loss of day length due to the sun’s movement from the northern to southern hemisphere, which may also result in undesirable shade patterns significantly impacting the ability of turfgrass to function properly. This causes decreased health, density, and vigor in grass stands.

Working With the Shade Instead of Against It

Since turfgrass managers cannot change the seasonal position of the sun, at times, there are challenges associated with shade imparted by trees and structures. Innovative ways of improving turfgrass photosynthetic capability are critical to ensure optimum plant health. A novel mechanism might be to supplement natural photosynthesis from sunlight with artificial photosynthesis powered by acetate in the form of potassium (K) acetate. Some evidence exists suggesting that exogenous applications of acetate in low light conditions can be a source of carbon and energy for plants (A hybrid inorganic–biological artificial photosynthesis system for energy-efficient food production | Nature Food). Our Harrell'sMAX® product Stress Relefe, 0-0-25, is a great source of potassium acetate to supplement your lawn and is the product used throughout this article and the trials below.

A growth chamber study was conducted at Virginia Tech University under the direction of Dr. Xunzhong Zhang to explore the potential value of Stress Relefe applications to creeping bentgrass growing under shade cloth. The shade cloth only allowed 70% photosynthetic active radiation to reach the canopy, creating an environment very similar to what your lawn might receive.

Below, you will find the results of his research.

Stress Relefe Treatments (applied biweekly)

1. Fertilized control biweekly (0.10 lb N/1000 ft² from fertilizer 28-8-18 biweekly)

2. Stress Relefe 3 fl oz/1000 ft²/week + fertilized control biweekly

3. Stress Relefe 3 fl oz/1000 ft²/biweekly + fertilized control

4. Stress Relefe 6 fl oz/1000 ft²/biweekly + fertilized control

The rate of N fertilization (from 28-8-18) for treatments 2, 3, and 4 was the same as treatment 1 (fertilized control) so all four treatments received identical N input.

Preliminary Results

Turf quality

Foliar application of Stress Relefe at 3 and 6 fl oz/1000 ft² biweekly improved turf quality relative to the control as measured on Day 14 and Day 28, and all three Stress Relefe rates improved turf quality relative to the control as measured at Day 42 and 56 (Table 1, Photo 1). The best turf quality was achieved when Stress Relefe was applied at 3 fl oz/1000 ft² biweekly as measured at the end of the trial.

Root biomass

Foliar application of Stress Relefe at 3 fl oz/1000 ft² weekly or biweekly and 6 fl oz/1000 ft² biweekly improved root biomass relative to the control. The greatest root biomass was found in the grass treated with Stress Relefe at 3 fl oz/1000 ft² biweekly (Table 2, photo 2).

Photo 1. Turf quality response to Stress Relefe application as measured at

The end of the trial (day 56).

Photo 2. Root growth response to Stress Relefe application was measured at the end of the trial (day 56).

I’d like to acknowledge Daniel Stover for his significant contribution to the initiation of this study. By sharing his observations associated with the positive effects of potassium acetate applications on his turfgrass impacted by shade, he helped us a great deal to develop our findings.

Most recent update: Dr. Zhang's most recent update shows that Stress Relefe increased photochemical efficiency, leaf chlorophyll content, and leaf protein content. This information adds support as to why Stress Relefe improved turf quality and root biomass, while overall functioning better in the treatments.

For more lawn maintenance, control strategies, or questions on Harrell'sMAX® Stress Relefe, 0-0-25, reach out to your local Harrell's rep. And if it's time to hit the "reset button" on your lawn, check out this article from Harrell's Director of Agronomy Dr. Paul Giordano.