Improving spring establishment of creeping bentgrass by reducing light intensity

May 28, 2024

By Alec Kowalewski, Oregon State University and Dominic Petrella, Ohio State University

The shoulder seasons can have dramatic temperature changes during the day and large differences in lows/highs from day-to-day, especially during the winter-to-spring transition window. Lows can often be near or below freezing and daytime highs might be around freezing or as high as 80°F in many parts of the northern U.S. Unfortunately, if you have winterkill, and you are forced to re-seed during this timeframe, the weather is usually not cooperative, resulting in stressful conditions for the seedlings. An often overlooked piece during this seasonal shift is light intensity. In some regions it can often be very sunny on days where it is still cold in the morning or stays chilly throughout the day. These conditions, bright and cold/chilly, are stressful for plants in general, and can be more stressful for seedlings.

a series of five images; the first is a set of turfgrass samples in the growth chamber grown under different levels of shade, the second is looking down at three turfgrass samples alongside a graph of gain in turf cover by % shade at two different temperatures, the third is shade cloths covering turfgrass samples in the field, and the fourth is a graph of % change in cover by % shade — Figure 1. A&B) In growth chamber experiments, creeping bentgrass cultivars such as ‘007’ established much better when grown at 50°F for 7 days when light intensity was reduced by 90% (≈100 µmol m-2 s-1; 0% was ≈800 µmol m-2 s-1). C&D) We also tested this in the field by growing plants under “optimal” conditions in a growth chamber then transferring to the field in mid-March in St. Paul, MN and found that reducing light intensity during cold snaps can result in improved establishment.

The stress resulting from the combination of high-intensity light and low-temperature is called low-temperature photoinhibition. With this, light itself damages the photosynthetic machinery in the plant, and is exacerbated by the low-temperature. This can slow growth dramatically, decreasing the success of spring overseeding. This stress could be reduced by decreasing light intensity during these periods. We have looked at low-temperature photoinhibition in a series of creeping bentgrass cultivars, and found that reducing the light intensity during these cold snaps (50°F) can significantly reduce stress and improve establishment (Figures 1 and 2).

a set of three figures; the first is of turfgrass from the growth and under special lighting to indicate plant stress, the second a graph of % shade by photosynthetic stress, and the third a graph of cultivar by photosynthetic stress. — Figure 2. Along with better establishment, plants were also much less stressed when light intensity was reduced. A) Both ‘Penncross’ and ‘Memorial’ creeping bentgrass were stressed significantly less when light intensity was reduced by 50 and 90% in both growth chamber and field experiments (blue pixels indicated healthier leaves; green pixels indicate more stress). B) Fv/Fm data (a measure of photosynthesis stress), show that lower light intensity during cold periods results in less stress, but there were no differences across C) cultivars tested.

We are currently scaling this approach and testing if reducing light intensity on spring-seeded creeping bentgrass improves establishment by reducing stress during periods of cold snaps in field plots. This is being evaluated at Oregon State University, University of Minnesota, University of Wisconsin, Michigan State University, Iowa State University, and in Norway. For this we are seeding ‘Luminary’ creeping bentgrass, and after plants have germinated, placing shade cloth that reduces light intensity by 70% over the plots for either 7, 14, 21, or 28 days and evaluating turfgrass establishment.

Recent results from Oregon State University

research area divided into plots by string; some of the plots have seed envelopes on them. In the background is equipment and people examining other research plots — Figure 3. Creeping bentgrass research plots seeded April 11, 2024 in Bend, OR.

To evaluate the relationship between light intensity and spring growth and development in Central Oregon, creeping bentgrass was seeded April 11, 2024 at the Pronghorn Resort in Bend, OR (Figure 3). All plots were covered with a germination blanket from April 11 to April 25. On April 25, the germination blanket was removed, and shade cloth structures were placed over the creeping bentgrass with the exception of a control treatment that did not have a shade structure (Figure 4). These shade structures are being removed in subsequent order at 7, 14, 21 and 28 days (May 2, 9, 16 and 23, respectively).

turfgrass field research plots with black shade cloths on wood frames. — Figure 4. Shade structures that were placed on April 25, 2024.

Preliminary findings suggest that the shade structures improve turfgrass establishment based on percent cover, visual quality, and normalized difference vegetation index (NDVI) values. It is yet to be determined how long these shade structures should remain, but preliminary data would suggest a minimum of 7 days after germination. It is important to note that in Central Oregon temperatures this May have regularly been around freezing in the morning, and in the 60s and 70s in the afternoon. There have also been a few light snow flurries in April. These conditions are quite regular for a spring in Central OR. While these results are promising, more data is needed before we can determine if this approach should be used by turfgrass managers. Unfortunately, the particular combination of environmental conditions needed for photoinhibition will not occur at every one of our research locations each year; we hope that over the next few years to confirm these results at other WinterTurf research sites.