Yellow Spot Disease of Sedge at Binh Minh - Kim Son - Ninh Binh and Nga Son - Thanh Hoa

Abstract

Yellow spot disease of sedge was identified to be caused by an oomyces, Phytophthorasp. In spring season, 2009, the disease developed remarkably from the end of March until the end of April (with incidence 6.88% and severity of 1.44%). At this time, the height of sedge is 1.6 m. However, the development of the disease was stopped in May and June. In summer, the disease developed from mid-August to mid-September. At Binh Minh, the incidence was 4.88% and severity was 1.0% on 18 August. The figures were 4.21% and 0.99%, respectively at Nga Tan - Nga Son on 16 August. From late September to early October, the disease gradually reduced as the dry weather with little rain is not favorable for the development of the disease. The disease incidence and severity of the four-year-old sedge plants were higher than that of one and two-year-old plants. The pathogen grew well on the Pea-agar medium with colony diameter of 62.5 mm after 10 days of culturing. The inoculation of the 10 - 30-day plants showed higher rate of infection (incidence 60-80%) compared with the inoculation of the older plants (90 - 100 days after cutting)