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Significance

Phytophthora ramorum is a recently emerged pathogen, thus the ultimate significance of SOD and ramorum blight is still unknown. Without a thorough understanding of the pathogen’s biology, it is still too early to predict the magnitude and future impact of this disease. The climate in coastal areas of Washington, Oregon, and California as well as large areas of the southeastern U.S. is considered suitable for P. ramorum (Figure 27). The fear is that this disease could spread by infested nursery plants to the eastern U.S. where susceptible oak-hickory, oak-pine, and lowland oak forests account for 67.8 million ha (167.5 million acres), or 46% of the total area classified as timberland. In greenhouse tests, several important east coast tree species were found to be highly susceptible to the disease.

Figure 27

Other exotic Phytophthora species have led to extensive tree mortality and negative ecological impacts in Australia, Europe, and North America. The desire to prevent an outbreak as devastating as historical epidemics like Dutch elm disease and chestnut blight has led to cooperative efforts between governmental officials, business owners, academia, and the public.

SOD has already changed the landscape of coastal California forests, where it is estimated that over 1 million trees have been killed in the last 10 years. The disease is lethal to the multiple oak species and tanoaks that make up a substantial part of several mixed-evergreen forest types in California, thus it will greatly alter the composition of these forests. Wildlife habitats will be affected. Since dead trees create an enormous fire hazard, fire management strategies will have to be considered in areas heavily hit by the disease. The ecological implications of this epidemic are as yet unknown.

P. ramorum has also placed a financial burden on the nursery industry on the west coast. Nursery sales make up a substantial portion of the agricultural economy for all three states currently under quarantine, and ramorum blight affects some of the most profitable and popular nursery crops for interstate commerce. Crop destruction, loss of sales, new disease management practices, inspections, training, testing, and increased documentation have required a huge commitment of both time and money. P. ramorum has forced many changes in the nursery industry nationally, highlighting the need for more effective methods for dealing with quarantine pests and pathogens.

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