Biological and chemical control of Phytophthora ramorum

Augmentation of soil leachate with 8 mu g of grapefruit extract/cm(3) almost completely inhibited the formation of Phytopthora ramorum zoosporangia. However, for complete inhibition of chlarnydospore production 200 mu g of grapefruit extract/cm(3) was necessary. Applied as a rhododendron spray 48 hr before leaf and stem inoculation with P. ramorum, the bioproduct inhibited the spread of necrosis by at least 50%. From 5 tested fungicides all inhibited zoosporangia formation, though Fenamidon + Fosetyl-Al and Furalaxyl were the most effective. All chemicals applied as rhododendron spray significantly inhibited colonisation of leaf blades and stems by P. ramorum, though Furalaxyl was the most effective. Additionally Fenamidon + Fosetyl-Al strongly inhibited the production of chlamydospores.