Title: Is stump sprout treatment necessary to effectively control Phytophthora ramorum in California's wildlands?
Author: Valachovic, Yana; Cobb, Richard; Rizzo, David; Twieg, Brendan; Lee, Chris; Glebocki, Radoslaw;
Source: In: Frankel, S.J.; Kliejunas, J.T.; Palmieri, K.M.; Alexander, J.M. tech. coords. Proceedings of the sudden oak death fifth science symposium. Gen. Tech. Rep. PSW-GTR-243. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 114-117
Publication Series: General Technical Report (GTR)
In California, wildland hosts that support sporulation of Phytophthora ramorum, such as California bay laurel (Umbellularia californica (Hook. & Arn.) Nutt.) and tanoak (Notholithocarpus densiflorus (Hook. & Arn.) Manos, Cannon & S.H. Oh), also develop prolific basal sprouts following mortality, injury, or tree harvest. Assessing long-term silvicultural treatment effectiveness for P. ramorum control is complicated by this stimulation of basal sprouting following tree removals. To better design P. ramorum treatments, we need to know how sprouts regenerating from cut host tree stumps are involved in local persistence of P. ramorum. These sprouts could act as reservoirs to maintain inoculum levels as forests regenerate and/or serve as points of re-invasion from vegetation surrounding treatment areas.
Following host tree removal treatments of infested stands in 2006, stump sprouts showed little infection for at least 3 years, suggesting that younger sprouts were less likely to become infected, or that climate was perhaps simply not suitable for the pathogen during these initial years, or both. To help clarify these issues and determine whether manual removal of sprouts after host tree removal is necessary to control pathogen persistence and reestablishment, we established two different sprout cohorts alongside each other in 2011 in areas at three sites where hosts were removed in 2006.
One year after we established this study, it appears that California bay laurel sprouts that were manually cut in 2011 were less likely to be infected than nearby untreated sprouts that had grown for 7 years. Tanoak sprouts manually cut in 2011, on the other hand, show similar infection rates to nearby tanoak sprouts that were left uncut. At two of the sites, infection rates on both treated and untreated tanoak stump sprouts in 2012 have remained low, similar to pre-treatment levels. However, the other site presented high-infection rates in 2011 on tanoak, and both tanoak sprouts re-growing after cutting in 2011 and their 7-year-old paired sprouts were infected in 2012.
Keywords: Phytophthora ramorum, sudden oak death, sporulation, stump sprout treatment
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Valachovic, Yana; Cobb, Richard; Rizzo, David; Twieg, Brendan; Lee, Chris; Glebocki, Radoslaw. 2013. Is stump sprout treatment necessary to effectively control Phytophthora ramorum in California's wildlands?. In: Frankel, S.J.; Kliejunas, J.T.; Palmieri, K.M.; Alexander, J.M. tech. coords. Proceedings of the sudden oak death fifth science symposium. Gen. Tech. Rep. PSW-GTR-243. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: 114-117.
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