RAISED BEDS AND METALAXYL FOR CONTROLLING PHYTOPHTHORA ROOT-ROT OF RASPBERRY

'Titan' red raspberry (Rubus idaeus L.), highly susceptible to root rot caused by Phytophthora fragariae Hickman var. rubi Wilcox & Duncan (syns. P. erythroseptica Pethyb., ''highly pathogenic'' P. megasperma Drechs.), was planted in June 1990 in a silt loam naturally infested with the pathogen. Raised beds (0.36 m high) dramatically reduced disease incidence and severity relative to flat bed treatments. In contrast, metalaxyl at 372 mg.m-1 of row provided little benefit when applied to flat beds and provided consistently moderate but statistically insignificant effects when applied to raised beds. Relative to the flat bed system, primocane vigor was increased in 1992 by 16%, 190%, and 224% in the flat bed plus metalaxyl, raised bed, and raised bed plus metalaxyl treatments, respectively; total yields were increased by 7%, 231%, and 272% with these same respective treatments. The results indicate that raised-bed planting systems can provide substantial control of phytophthora root rot of red raspberries even when highly susceptible varieties are grown on otherwise marginal sites. Metalaxyl appears more effective as a supplement rather than substitute for raised beds under such conditions. Chemical name used: N-(2,6-dimethylphenyl)-N-(methoxyacetyl)alanine methyl ester (metalaxyl).