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Shedding light on growing turfgrass in shade

By |  March 3, 2017 0 Comments

Dave Gardner, Ph.D., is a turfgrass scientist at The Ohio State University. Gardner has conducted several shade-related research projects to help superintendents better understand what is happening to turf plants in shade and how to help turf in the shade perform better. Dave can be reached at gardner.254@osu.edu for more information.

Q: Describe the shade used in your research.

We were concerned in our research about both the quantity and quality of light reaching the turf. Light quantity was measured using photosynthetic photon flux and light quality was measured by the ratio of red: far red (R:FR) light reaching the turf.

We used three types of shade. The first was full, natural sunlight, the second was uniform shade created by a stand of deciduous trees, and the third was shade created from using a heavy, aged plastic cover over a hoop house. The quantity and quality of sunlight received in the natural sun plots was used as our reference point for comparisons. Plots under the deciduous trees received about 9 percent to 10 percent of the quantity of light and low R:FR light ratio compared with plots in natural sun. Plots under the hoop house received about 9 percent to 10 percent of the quantity of light and a similar R:FR light ratio compared with plots in full sun.

This gave us the opportunity to compare tall fescue turf in full sunlight with tall fescue grown under reduced quantity and quality of light in the deciduous shade and with tall fescue grown under reduced quantity but the same quality of light under the hoop house.

Q: How did the tall fescue respond to these three light environments?

Compared with tall fescue in full natural sunlight, turf under deciduous tree shade had approximately 50 percent less leaf area, tiller density decreased about 60 percent, chlorophyll content remained about the same, epidermal cells were thin, misshapen or absent and root density declined about 80 percent. Again, compared with tall fescue in full natural sunlight, turf under hoop house shade grew taller, had about the same leaf area, tiller density decreased about 30 percent, chlorophyll content was higher, epidermal cells remained the same and root density declined about 80 percent.

We concluded from these results that light quality has a major impact on turfgrass response to shade, and that when we think about shade stress we need to think about both light quantity and quality. The reduction in root density is a good reminder that turfgrass plants growing in shade will prioritize leaf growth over root growth. This makes sense from a survival point of view.

Q: What are the practical implications of your results?

One of the practical things we considered was tree removal or tree thinning on golf courses. Most decisions regarding which trees to remove or branches to cut off are based on mobile devices that measure sunlight quantity. Based on our research, selective removal of branches may not have as much positive impact on turf performance as we had hoped. While removing some branches may increase light quantity reaching the turf, the light is still being filtered by the remaining tree canopy, and light quality declines. It is the changes caused by altered light quality that are more damaging to the turf compared with just reduced light quantity.

To make a positive impact on turf performance, keep in mind that direct, unfiltered sunlight must reach the turf. The more hours of direct, unfiltered sunlight that reaches the turf the better.

Our research confirms that turf growing in shade is less tolerant to all stresses, particularly traffic stress. The increased disease susceptibility to turf growing under deciduous tree shade may be due to changes in the epidermal cell layer making it easier for fungal hyphae to penetrate the leaves.

This is posted in Columns, Featured

About the Author: Clark Throssell, Ph.D.

Clark Throssell, Ph.D., is the former director of the Purdue University turf program as well as the former director of research for GCSAA. Throssell is the research editor for Golfdom, focusing on managing the Super Science section of the magazine and website. He also contributes his "Clark Talks Turf" column to Golfdom every month.


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