Sudden Oak Death (SOD) was first reported in 1995 in central coastal California. Since then, tens of thousands of tanoaks (Lithocarpus densiflorus), coast live oaks (Quercus agrifolia), and California black oaks (Quercus kelloggii) have been killed by the fungus, Phytophthora ramorum. On these hosts, the fungus causes a bleeding canker on the main stem of the tree which grows over a period of several years until it girdles the tree. This effectively eliminates the tree’s ability to move adequate amounts of water from the roots to the crown. On the host plants the fungus causes leaf spot and twig dieback, and doesn’t kill these species. The hosts serve as spore factories for the fungus which can inundate a forest understory under the ideal environmental conditions.
As of January 2002, the disease was known to occur only in California and southwestern Oregon; however, transporting infected host plants may spread the disease. The pathogen has the potential to infect oaks and other trees and shrubs elsewhere in the United States. Limited tests show that many oaks are susceptible to the fungus, including northern red oak and pin oak, which are highly susceptible.
In March of 2004, select camellia varieties from a nursery in California were identified as being infected with the pathogen. Two other nurseries in Oregon were also found to have infected plants in the summer and fall of 2004. A total of 59,000 potentially infected plants were shipped to Georgia. While 10,000 plants were intercepted by the Department of Georgia Agriculture, 49,000 plants were sold before Georgia was informed of the SOD infected shipment. It is unknown how many of these 49,000 plants, if any are infected. Sudden Oak Death pathogen has now been found in 17 nurseries throughout Georgia.
Georgia Department of Agriculture nursery inspectors inspect plants imported into our state, and continue to intercept some infected nursery stock each year. The Georgia Forestry Commission samples native vegetation surrounding these nursery sites as well as from forested areas throughout the state and to date, no native plants have been infected with this pathogen in Georgia. The Georgia Forestry Commission continues to work closely with other agencies such as the Georgia Department of Agriculture, University of Georgia, U.S. Department of Agriculture Forest Service and the USDA Animal and Plant Health Inspection Service.
About half of Georgia’s 24.7 million acres of forestland contain oak trees.
Scroll down to read a summary of Sudden Oak Death from 2006.
Sudden Oak Death Summary in Georgia
Source: James Johnson and Mark Raines, Georgia Forestry Commission
The Sudden Oak Death monitoring program continues. One nursery in Georgia was confirmed positive for Phytophthora ramorum in 2006 (by USDA Animal & Plant Health Inspection Service (APHIS)). This brings the total to 16 nurseries in Georgia with infected nursery stock since 2004. The GFC provided on site assistance with the burning of these plants (along with Georgia Department of Agriculture (GDA) and APHIS officials). Georgia had 0 homeowner positives in 2006 and the number of homeowner samples being tested continues to decline as the media coverage on the SOD threat has also declined. The GFC checked 51 trace forward nursery locations with our perimeter surveys and 3 homeowner, and 10 forest sites. No positives have been found on native vegetation. The GFC is helping fund the costs associated with operating the plant pathology lab at the University of Georgia (UGA) that does the testing for Georgia. The Georgia Department of Agriculture (through APHIS) is also providing funds for this lab, and approximately 7,200+ samples have been processed along with 84 confirmed positives on nursery stock from 2004-2006 to date through this lab.
Georgia’s stream baiting continues in 2006 and 10 sites were chosen in northeast Georgia to detect the presence of Phytophthora ramorum. Ten forest (vegetation) sites were chosen within these watersheds also. Four of these sites are in close proximity to nurseries that were known to have infected plants in 2004 (and one was a repeat in 2005). The University of Georgia, in cooperation with Georgia Department of Agriculture and the national nursery survey, is water sampling and stream baiting the irrigation water within 6 nurseries also. Future stream baiting efforts will target more watersheds near other positive nurseries in the metro Atlanta area with the belief that many of these plants were sold and planted locally and could be causing further Phytophthora ramorum infections in the landscape undetected.
In 2003-04, the best estimate is that 59,000 West Coast plants (from positive Phytophthora ramorum nurseries) were imported into Georgia. Georgia Department of Agriculture intercepted 10,000 of these plants and they were destroyed, but the other 49,000 potentially infected plants were sold and planted in landscapes within the state. It is estimated that 1-2% of these might be infected with Phytophthora ramorum but at one of the 16 positive nurseries (on the coast) had a 60% infection rate for samples processed. This percentage is likely skewed somewhat since only symptomatic leaves were sampled but the coastal region of the state is indicated as low risk on the national risk map and this may not take into account the coastal climate factor. Two of the three homeowner positive plants came from this small nursery.
A positive camellia plant was retrieved by APHIS, GDA, UGA, and GFC. The infected plant, mulch within 6 feet and potting soil in the planting hole were removed and incinerated. The area was sampled in 2004-06 and no positives on these established plants have been detected. Other known hosts include azaleas, vaccinium, roses, and the Georgia State Tree: Live Oak (Quercus virginiana).
Who is Involved
State (Georgia Forestry Commission, University of Georgia, Georgia Department of Agriculture) and Federal (USDA Forest Service, USDA Animal & Plant Health Inspection Service) agencies recognized the threat this disease posed to eastern forests and formed a Sudden Oak Death Action Committee (SODAC) in 2001 to consolidate efforts.
Georgia continues to have a coordinated sudden oak death program and communication with all partners remains a priority, and survey efforts are coordinated. A proactive plan was implemented in 2005 to inform the public and green industry about getting plants checked (if they meet certain criteria), and the procedures that will be followed if infected plants are detected.
Working with Georgia Nurseries
The Georgia Forestry Commission participated in a series of town-hall type meetings held throughout the state targeting Georgia nurseries. These meetings were hosted by the Georgia Green Industry Association (GGIA) and the outcome was a task force that formulated a set of voluntary BMPs for Georgia nurseries that will minimize the introduction of infected nursery stock. State funding to process the samples has not been secured and the program has not been fully implemented. This set of guidelines was patterned after the Canadian Phytophthora ramorum exclusion program.
A green industry task force developed a voluntary SOD best management practices manual for Georgia nurseries that was unveiled at the annual green industry meeting in Athens in January 2006. Although interest is keen among some growers, the UGA lab simply can’t process the number of samples that would be required to implement the program. The group is seeking state funding at this time to allow the lab to step up sample processing numbers.
Training has been given to all GFC foresters on Phytophthora ramorum, and the threat from this pathogen poses has been explained in detail at 50+ training sessions (presented by either the GFC Forest Health Staff or University of Georgia â€“ Plant Pathology Department) to resource professionals throughout the state.
Outreach to the Public
Efforts are being made to alert the public of the risk our forests face from sudden oak death disease, and to test suspect plants at our lab. Numerous newspaper articles have been published along with a GFC Sudden Oak Death brochure. Despite these efforts, less than 1000 of the 49,000 suspect plants have been tested to date.
Oak Resource and Estimated Value
According to 2004 Forest Inventory Analysis (FIA) data, Georgia has approximately 9.7 million acres of Oak-type forest and 24.7 million total forested acres.
FIA data indicates 15.8% of all forest trees are oak spp.
The total estimated value of oak in Georgia is $33,237,252,000 (James Johnson, GFC):
- $ 22,895,340,000 – Urban forests (Nowak et al., Journal of Forestry 99 (3), pp. 37-42)
- $ 7,541,612,000 – Growing Stock – standing timber (1997 FIA data)
- $ 1,100,300,000 – Tourism (Georgia Industry, Trade, & Tourism)
- $ 1,700,000,000 – Wildlife-consumptive & non-consumptive uses (Georgia Department of Natural Resources)
Survey – 2006
Georgia’s detection surveys have been a combination of nursery perimeter, surveys at trace forward locations (which include the 16 positive sites), forest and homeowner surveys, and stream baiting. Sudden Oak Death Survey Map 2006 West Coast Officials Visit Georgia
In May 2005, the Georgia Forestry Commission hosted a group of west coast nursery and regulatory officials to illustrate the risk of Phytophthora ramorum in our eastern forests. Steve Oak, USDA Forest Service, and James Johnson, GFC, took the group to a high risk forest setting to illustrate the understory host species that could facilitate spore production and oak infections. This tour was part of a southeastern nursery tour throughout multiple states and Georgia Department of Agriculture were the guides for the trip. This stop was the only one involving a general forest setting.