Efficacy of DMI Fungicides As Stress Protectants.

Agrostis stolonifera is a common turfgrass species found on golf course putting greens.  However, due to close mowing heights, management practices, and environmental factors, it is often put under stress that affects its ability to maintain high performance and aesthetic characteristics.  Applications of propiconazole and tebuconazole are commonly made to control diseases, but little is known about the effect they may have on carotenoid accumulation in Agrostis stolonifera.  Applications of DMI fungicides inhibit GA biosynthesis in plants.  By blocking the GA pathway, we hypothesize that the result may be a shift of metabolic precursors from normal GA synthesis to the carotenoid pathway.  Since carotenoids act as powerful antioxidants, an increase in the products of the carotenoid pathway may result in improved stress tolerance in turfgrass.  Two applications of propiconazole at 0, 976 and 1952 g ha^-1 and tebuconazole at 0, 1527, and 3054 g ha^-1 were made seven days apart.  Seven days after the second application, water was withheld until the volumetric water content measured six percent soil moisture reached approximately six percent.  Clippings were collected four times and carotenoid and chlorophyll pigments were extracted from fresh frozen leaf blades and measured using high performance liquid chromatography HPLC to determine effects of treatments on carotenoid metabolism.  Measurements of leaf blade F_v/F_m and digital image analysis were also taken to determine plant stress.