The distribution and incidence of white pine blister rust in central and southeastern Wyoming and northern Colorado

Abstract

A survey of limber pine (Pinus flexilis James) to determine the geographic distribution, incidence, and severity of white pine blister rust (WPBR) throughout 13 study areas in central and southeastern Wyoming and northern Colorado was conducted from 2002 to 2004. The majority (81.1%) of the 18 719 surveyed limber pines >1.37 m tall were classified as healthy, 13.5% were declining or dying from various causes, and 5.4% were dead. WPBR was present on 278 (55%) of the 504 survey plots. Incidence of the disease ranged from 0% to 100% and averaged 15.5% over all the plots and 28.0% on the infested plots. Likelihood of infection by WPBR was significantly greater for limber pines in larger diameter classes. Incidence was negatively correlated with elevation and positively correlated with geographic position, with more northerly and easterly plots having higher incidences of WPBR. Incidence varied by slope position and did not vary by aspect, slope configuration, or degree of canopy closure. The current level of infestation in central and southeastern Wyoming and northern Colorado has been attained within the past two to four decades. With time, the pathogen may spread to currently uninfested white pine populations and intensify throughout its current distribution impacting valuable ecosystems.Résumé : Un inventaire du pin flexible (Pinus flexilis James) a été réalisé de 2002 à 2004 dans 13 zones d'étude situées dans le centre et le sud-est du Wyoming et le nord du Colorado pour déterminer la répartition géographique, l'incidence et la sévérité de la rouille vésiculeuse du pin blanc (RVPB). La majorité (81,1 %) des 18 719 pins flexibles échantillonnés de plus de 1,37 m de haut ont été classés comme sains, 13,5 % dépérissaient ou étaient mourants sous l'effet de diverses causes et 5,4 % étaient morts. La RVPB était présente dans 278 (55 %) des 504 places-échantillons. L'incidence de la maladie variait de 0 % à 100 % et atteignait en moyenne 15,5 % dans l'ensemble des places-échantillons et 28,0 % dans les places-échantillons infectées. Les risques d'infection par la RVPB étaient significativement plus élevés pour les pins flexibles dans les classes de diamètre supérieures. L'incidence était négativement corrélée avec l'altitude et positivement corrélée avec la position géographique : les places-échantillons les plus au nord et les plus à l'est avaient les plus fortes incidences de RVPB. L'incidence variait selon la position de la pente mais non selon l'exposition, la configuration de la pente ou le degré de fermeture du couvert. Le niveau actuel d'infection dans le centre et le sud-est du Wyoming et le nord du Colorado a été atteint au cours des deux à quatre dernières décennies. Avec le temps, le pathogène pourrait progresser vers les populations de pin blanc non infectées et l'infection pourrait s'intensifier partout où la maladie est actuellement présente et affecter des écosystèmes de grande valeur.[Traduit par la Rédaction]

Limber Pine Regeneration and White Pine Blister Rust in the Central and Southern Rocky Mountains

“…We used 238 previously sampled (Kearns and Jacobi 2007) and 270 previously unsampled stands for this study. A stratified random sample of Kearns and Jacobi's (2007) plots from [2002][2003][2004] was used to ensure a relatively equal number of plots with no or low rust incidence and high rust incidence and the presence or absence of bark beetle activity.…”

“…Fisch., and, more recently, by mountain pine beetle (Dendroctonus ponderosae Hopk.) are having an impact on limber pine (Pinus flexilis James) stands in the Rocky Mountains (Kearns and Jacobi 2007, Burns et al 2011, US Department of Agriculture [USDA] Forest Service Rocky Mountain Region 2014, Cleaver et al 2015) and are consequently affecting regeneration. C. ribicola is capable of infecting five-needle white pines in the subgenus Strobus, has a complex life cycle requiring five spore stages, and uses species of Ribes, Castilleja, and Pedicularis (McDonald et al 2006, Mulvey andHansen 2011) as alternate hosts.…”

Options for the management of white pine blister rust in the Rocky Mountain Region

“…Thinning may also lead to increases in Ribes, which thrives in full sunlight. Similarly, Kearns (2007) found that the incidence of blister rust was higher on open-grown limber pines than on intermediate or overtopped trees. Thinning may be an appropriate management strategy under certain circumstances, especially if combined with pruning.…”

“…Geils, personal communication). Kearns (2007) recently completed the most comprehensive survey of central and south-central Wyoming and for the first time, reported the disease in the Medicine Bow and Sierra Madre Mountains (Kearns and Burns 2005). Incidence of WPBR was greatest in northern Wyoming Table 1-Ribes species that grow in association with white pine populations in the Rocky Mountain Region and their potential for contributing to the spread of white pine blister rust (Kearns 2005;Van Arsdel and Geils 2004 and in areas where the disease has been present for decades.…”

“…These are often referred to as "wave years." In the Rocky Mountain Region, the disease is more prevalent in valley bottoms and at lower elevations, presumably where these conditions occur more frequently (Burns 2006;Kearns 2007). …”