Date of Award
Master of Science (MS)
Plant and Environmental Science
McCarty, Lambert B
Faust , Jim E
Toler , Joe E
Liu , Haibo
Shade or low light tolerance is an increasingly important issue to turf managers as they are often expected to grow turf in less than ideal agronomic conditions. As permanent structures such as residential buildings add to already problematic shade caused by trees, and other barriers, new solutions are needed to help turf managers provide acceptable turf conditions. The plant growth regulator trinexapac-ethyl (TE) can lessen negative responses of turfgrass to shade.
Two experiments were conducted during the summers of 2008 and 2009 to evaluate various grasses under a reduced light environment (RLE). In the first study, performance of `Diamond' zoysiagrass in a RLE was evaluated when maintained under putting green conditions. In a second study, performance of various cultivars of zoysiagrass [Zoysia japonica Steud.] [Zoysia matrella (L.) Merr.] and bermudagrass [Cynodon dactylon (L.) Pers. x C. transvaalensis Burtt-Davy] were evaluated under a RLE.
Both studies included three levels of shade: (0, 60, and 90%) and two levels of trinexapac-ethyl (0 and 0.57 kg ai ha-1 wk-1 Primo MAXX 1 EC). TE treatments were applied with a CO2 backpack operating at 189.5 L ha-1 (20 GPA) with an 8003 flat flan nozzle. Application of shade was initiated on 23 May 2008 and removed 30 October 2008. In 2009 application of shade was initiated 24 May and removed 31 October. Plot size in the first study was 2m by 1.5m. Shade structures were maintained at a height of 45 cm above ground level to maintain proper airflow. Shade tents were removed 2 hours weekly to take measurements and perform maintenance.
In the first study, application of Trinexapac-ethyl to 90% shade increased turf quality by ~4 units from 1 to ~5 at the end of each study year. While still not commercially acceptable (TQ≥7), some turf cover was still preserved. Other plant responses measured included percent lateral regrowth (LR), total non-structural carbohydrates (TNC), clipping yield, ball roll distance, and total shoot chlorophyll. Lateral regrowth increased initially with shade application until plant health declined, leading to decreased LR. Application of TE decreased LR by limiting plant growth. Total non-structural carbohydrates decreased with increasing shade application, and increased with TE application. Clipping yield initially increase in both 60% and 90% RLE, then declined as plant health declined. Application of TE slowed clipping yield production at the beginning of the study, then increased clipping yield at the end due to increase in plant health from TE application compared to treatments not receiving TE. Ball roll distance was decreased by 60% and 90% RLE initially. As plant health in 90% RLE without TE and 90% RLE + TE declined, ball roll distance increased due to declining turf cover. Chlorophyll concentration was increased by both 60% RLE with and without TE. Ninety percent RLE with and without TE reduced chlorophyll concentration.
In the second study, TQ decreased with increasing RLE level in all cultivars. At the end of both years, Diamond and Meyer zoysiagrass demonstrated the highest TQ in a 60% RLE out of all cultivars. In a 90% RLE, Meyer zoysiagrass demonstrated the highest TQ at the end of each year. Application of TE increased TQ of cultivars grown in 60% and 90% RLE. At the end of 2009, Meyer zoysiagrass + TE application was the only cultivar to maintain turf cover in a 90% RLE.
Clipping yield was initially increased in all cultivars by increased levels of RLE. Application of TE decreased clipping yield. As plant health declined, clipping yield also decreased. At the end of the study, TE application increased clipping yield as a result of increased plant health.
Initially, an increase was seen in chlorophyll concentration with increased levels of RLE. Application of TE to RLE treatments further increased chlorophyll concentration. At the end of each study, chlorophyll concentration decreased in 60% and 90% RLE treatments as plant health declined. Once again, as TE application increased plant health, chlorophyll concentration was increased.
Atkinson, Jeffrey, "RESPONSE OF WARM SEASON TURFGRASSES TO REDUCED LIGHT ENVIRONMENTS" (2010). All Theses. 984.