NC STATE UNIVERSITY
College of Agriculture and Life Sciences
Department of Plant Pathology
Extension

Sudden Oak Death and North Carolina Nurseries

Mike Benson, Professor

shoot dieback midrib infection
Typical shoot dieback on rhododendron caused by Phytophthora (left) and close up of expanding leaf infection due to P. ramorum (right)

In the spring of 2004, Phytophthora ramorum cause of Sudden Oak Death (SOD) and Phytophthora blight in California and Europe was found on camellias at two nurseries in southern California in a region outside the regulated counties in CA. Prior to inspection of these nurseries, camellias and viburnums were shipped to more than 1200 locations in 39 states some of which were unknowingly infected with P. ramorum. Through subsequent trace-forward inspections of these locations by the U. S. Department of Agriculture, Animal and Plant Heath Inspection Service, Plant Protection and Quarantine (USDA APHIS PPQ) working in cooperation with the North Carolina Department of Agriculture and Consumer Services, it was determined that eight of 44 locations in North Carolina with camellias still on site had received infected plants. A total of 54 locations in 11 states outside of California have received infected plant material as of May 2004. Federal eradication guidelines are being followed to destroy infected plants in North Carolina and elsewhere.

What should North Carolina nurseries do to avoid future problems with this federally regulated pathogen?

Be aware of the current host and associated host list for P. ramorum.

  • USDA APHIS PPQ maintains the official list of hosts and associated hosts of P. ramorum on their web site. Associated hosts are plants found in nature or nurseries with P. ramorum infection but for which the rules for pathogenicity [Koch's postulates] have not been completed.
  • The list is constantly being amended as new hosts and associated hosts are found in nature or in nurseries. Recently Pyracantha koidzumii was added to the associated host list based on a discovery in a Canadian nursery.

Know the geographical source of plant material you buy.

  • Since the pathogen has not been found, to date, in the United States in natural areas outside of the regulated areas in California and Oregon including a few nurseries in those states, the probable way for P. ramorum to be introduced to a North Carolina nursery is on infected plant material brought into the nursery from sources in California, Oregon, or Europe.
  • As a result of the nursery outbreak in southern California, USDA APHIS PPQ has put in place a requirement that all nurseries in California that ship hosts of P. ramorum or associated hosts interstate must be inspected each year. A list of nurseries that have been inspected and are in compliance, i.e. P. ramorum was not detected, as well as those nurseries in California that currently have P. ramorum infected nursery stock can be found on the California Department of Food and Agriculture web site.
  • The Oregon Department of Agriculture instituted a statewide survey of all nurseries in 2003 to confirm that P. ramorum was not present in Oregon nurseries. As a result of the survey one nursery was found with P. ramorum and infected nursery stock was destroyed to eradicate the infestation. Subsequent trace-forward surveys were done to recover and destroy plants shipped to other locations in Oregon and Washington by the nursery prior to the discovery of the pathogen at that nursery. Request a copy of the nursery inspection certificate if you buy plant material from Oregon nurseries.
  • In Europe, P. ramorum has become established in many nurseries. Again, know the source of plant material purchased from Europe and insist on a copy of an inspection certificate stating that the nursery has been certified free of this pathogen.

Take steps at the nursery to minimize the impact should P. ramorum be introduced.

  • Host and associated host plant material brought into the nursery from a location where P. ramorum has the potential to occur, i.e. California, Oregon, Europe and some Canadian regions should be unloaded in a way that associated leaf debris falling to the grown can be swept up and bagged for disposal by burial or burning. Likewise, if the shipping truck is completely emptied at your site, collect and bag debris for disposal once the truck is unloaded.
  • Designate an employee responsible for inspecting arriving hosts and associated hosts from high-risk areas to be sure foliar symptoms of Phytophthora dieback and blight are not present. This is important because even though a shipper may be compliant with their state agriculture department on a yearly basis, the pathology situation at a nursery can change within a week. Training sessions by Cooperative Extension plant pathologists and information on the Internet can help you become aware of Phytophthora foliar symptoms.
  • DO NOT DISPOSE OF SUSPECT OR INFECTED PLANTS OR PLANT DEBRIS IN YOUR CULL PILE AS THE PATHOGEN COULD MOVE INTO THE ENVIRONMENT. The goal of the federal regulation is to keep P. ramorum out of our eastern forests.
  • Newly arrived host and associated host plant material should be segregated from the general nursery population for at least a 60-day period favorable for plant growth and disease development (P. ramorum is most active at temperatures around 68 degrees F in the presence of moisture from rain or overhead irrigation).
  • Irrigation run-off from and rainfall on these plants should not be allowed to return to the retention basin used for general irrigation.

Re-think the way you lay out your blocks of plants.

  • The Federal "Confirmed Nursery Protocol" is very specific in the way "blocks" of infected plants are selected for destruction. A "2 meter, 10 meter rule" is applied. Plants that are hosts or associated hosts where P. ramorum has been detected will be destroyed until a distance of 2 meters (about 6 feet) of non-host or plant-free zone is encountered.
  • For most nurseries the "2 meter, 10 meter rule" means that only driveways not walkways will be wide enough to meet the 2 meter rule. Thus very large "blocks" of host and associated hosts could be destroyed by the regulation rules.
  • Therefore, it is important to re-think the way you lay out your nursery "blocks" so that you include "blocks" of non-hosts such as Japanese or Chinese hollies every so often. How often depends on how many host and associated hosts you are willing to see destroyed should P. ramorum be detected in that block.
  • Hosts and associated hosts within 10 meters of the non-host or plant- free zone will be held for 90 days and inspected twice for evidence of P. ramorum. During this 90-day period no fungicide may be applied to these plants.

Review your Integrated Pest Management (IPM) plan for your nursery.

  • Be sure sanitation practices are adequate.
  • Follow cultural practices to minimize the risk of Phytophthora infections such as irrigation schedules that allow foliage to dry completely before nightfall.
  • Evaluate the need for preventative fungicides sprays and drenches at your nursery.

More information on Sudden Oak Death and Phytophthora ramorum in nurseries can be found at the following web sites: