Wednesday, November 7, 2007
268-38
The Effects of Soil Organic Matter Content and Irrigation Frequency on the Severity of Pythium Root Dysfunction.
James Kerns, Plant Pathology, North Carolina State University, NCSU Department of Plant Pathology, 1133 Park Summit Blvd, Raleigh, NC 27523 and Lane Tredway, Campus Box 7616, NCSU Department of Plant Pathology, North Carolina State University, Dept. of Plant Pathology, Raleigh, NC 27695.
Symptoms of Pythium root dysfunction (PRD) have been observed on multiple golf courses in North Carolina since 2002. Symptoms develop into irregular patches ranging in diameter from 12 to 40 cm. Initially symptoms resemble wilt or drought stress then progress to an orange-yellow foliar decline. Our observations indicate that symptoms are most severe on newly renovated (<3 years), high-sand content putting greens. Two experiments were established in a growth chamber to determine the effects of organic matter content and irrigation frequency on PRD severity. To determine the effects of organic matter content on PRD severity, ‘A-1’ creeping bentgrass was seeded into cylindrical pots (15 cm dia., 30.5 cm deep) containing either 100:0, 90:10, 80:20, 70:30, or 50:50 % USGA greens specification sand: sphagnum peat moss. To determine the effects of irrigation frequency on PRD severity, cylindrical pots (15 cm dia., 30.5 cm deep) containing a sand meeting USGA specifications were established with ‘A-1’ creeping bentgrass. Irrigation treatments were initiated immediately after inoculation and lasted for 4 weeks. Treatments consisted of an application of 350 ml of water every 6, 4, 3, 2, or 1 day/s. Both experiments were arranged in a completely randomized design and were replicated over time. Twelve weeks after establishment, pots in both experiments were inoculated with a mixture of two highly aggressive Pythium volutum (Pv) isolates. Pots were placed in a growth chamber at 24C/16C with a 12hr day/night cycle. After 4 weeks, the temperature was increased to 32C/26C day/night to induce foliar symptoms. Once foliar symptoms develop, disease severity (0 to 100%) will be rated weekly for 4 weeks. Root depth and root mass will be measured prior to and after 4 weeks of heat exposure.