Stream monitoring updates

Three new positive waterways were identified in Georgia, Texas, and Washington in 2012 as a result of the National P. ramorum Early Detection Survey of Forests, bringing the total number of known positive sites outside of the established disease range in CA and OR to 15.  Seventeen states participated in the program, for a total of 114 stream baiting locations in all.  Of the 12 previously positive sites in AL, FL, GA, MS, NC, and WA, 11 were surveyed in 2012 and continue to be positive, reinforcing the trend of annual repeat detections once a site is initially confirmed.

The newly identified Texas stream was baited in response to positive soil findings at an associated nursery in the summer of 2012; however, no P. ramorum-positive plants were identified.  The last time the nursery had confirmed positive plants was in 2004 as a result of the nationwide P. ramorum-positive Camellia shipment.  Water baiting in the stream outside of that nursery was also conducted in 2010 and found negative.
Washington’s 2012 P. ramorum early detection survey of forests resulted in four positive water confirmations.  One of the sites was a new P. ramorum-positive location: a watershed sub-basin adjoining the Sammamish River, King County (which has been P. ramorum positive since 2007).  Three other locations were repeat positives for P. ramorum: one in a stream that feeds into the Sammamish River, one in the Sammamish River, and one in a Lewis County stream in a forested area.  None of the finds were in association with streamside plant infections.  In total, there were 12 baiting traps in 11 western Washington streams in 2012.  All baited streams were associated with nurseries previously identified with P. ramorum-positive plant stock.

The 2011 survey of water baiting methods (comparing in vitro baiting, Bottle O’Bait, and in situ baiting, bags) was expanded in 2012 and yielded consistent results with those obtained in 2011.  Sampling occurred at 25 positive sites in 6 states.  The pathogen was recovered by one or both assays in 139 comparable cases.  In vitro baiting was the more effective method overall (55 percent of recoveries); however, after analysis with 2011 data, it was clear the advantage was seasonally based, with spring being optimal.  The rate of P. ramorum recovery overall was lower in the fall, at which time in situ baiting was a more reliable method.  The pathogen was recovered by in vitro assay at nine sites over the two survey years when in situ baiting failed.  Without in vitro baiting, these sites would have been classified P. ramorum negative.  However, there was one site in 2012 where in situ succeeded and BOB failed.  Based on survey results, 2013 National P. ramorum Early Detection Survey of Forests cooperators will have the option of using either assay.  Unfortunately, due to budget shortfalls, it is anticipated that the 2013 program will be greatly reduced.

From the February COMTF newsletter.