Phytophthora ramorum
Detection of "P. ramorum" in watercourses has emerged as the earliest of early detection methods. This technique employs pear or rhododendron baits suspended in the watercourse using ropes, buckets, mesh bags, or other similar devices. If plants in the watershed are infected with "P. ramorum", zoospores of the pathogen (as well as other "Phytophthora" spp.) are likely present in adjacent waterways. Under conducive weather conditions, the zoospores are attracted to the baits and infect them, causing lesions that can be isolated to culture the pathogen or analyzed via PCR assay. This method has detected "P. ramorum" at scales ranging from small, intermittent seasonal drainages to the Garcia, Chetco, and South Fork Eel Rivers in California and Oregon (144, 352, and 689 mi2 drainage areas, respectively). It can detect the existence of infected plants in watersheds before any mortality from the infections becomes evident. Of course, it cannot detect the exact locations of those infected plants: at the first sign of "P. ramorum" propagules in the stream, crews must scour the watershed using all available means to find symptomatic vegetation.
Fungicide use in the United States
Crown and root rot of almonds is caused by at least 14 different "Phytophthora" species. The risk of root or crown infection is greatest during cool to moderate temperatures with prolonged or frequent soil saturation. A tree infected with "Phytophthora" can either undergo a period of slow decline that may last years or it can suddenly collapse and die in spring with the advent of warm weather. Eventually, leaves drop, terminal shoots die back, and death of the tree follows. Once in the root or crown the infection may extend into the crown, trunk, or branches. Currently, crown and root rot are a problem affecting 20% of California's almond orchards with potential yield losses of 50%.