![]() ![]() Significant increases in temperature such as those observed since that time have been linked to increased severity of pine wilt disease with many new cases documented in Colorado (Figure 4). 1984) were conducted close to 40 years ago. Additionally, other studies that suggested that PWN was not a significant threat to native trees in the U.S. where asymptomatic ‘carrier trees’ serve as disease reservoirs for PWN dispersal. Previous studies have shown that there are areas of the southeastern U.S. While mortality rates may be lower in ponderosa pine compared to many exotic species, persisting populations of PWN in ponderosa pine will increase the disease pressure faced in urban settings. The discovery of PWN in native ponderosa pine forests is concerning on two fronts. Figure 2 Figure 3 Is Pine Wilt a Potential Threat to Native Ponderosa pine forests? Flight phenology may vary greatly between species and locations on a larger scale (Boone et al. Sawyer beetles begin flight in early July and continue until October, with peak flight occurring between the last week of August and mid-September. Monochamus beetles and are typically considered secondary pests with minimal impact and management for Monochamus beetles is usually not recommended in absence of PWN. Transmission of PWN can also occur during egg-laying (Akbulut & Stamps, 2012). Primary transmission of PWN occurs when newly emerged adult beetles feed on the new shoot growth, typically in the early summer. scutellatus)that are native to western coniferous forests (Figure 3). In Colorado, PWN is vectored primarily by two species of wood-borer type beetles called sawyer beetles ( Monochamus clamator & M. However, as ponderosa pine becomes stressed, either through drought conditions or after a fire, they may become more susceptible to PWN. ponderosa) along the Front Range of Colorado (Figure 1) this native pine was previously thought to be resistant upon reaching maturity. In 2016, PWN was first isolated from declining and dead ponderosa pine ( P. 2014, Jacobi and Tisserat, 2015) along the Front Range and western slope of Colorado (Figure 2). After this occurrence, more reports emerged of PWN in dead Scots and Austrian pine (Blunt et al. In 2006, PWN was first reported in Colorado after being isolated from dead Scots pine. In the US, the westward movement of PWN has been tracked through Missouri and Kansas since 1979. and has caused widespread damage to forested landscapes where it has been introduced including Europe, Japan, South Korea, and China. ![]() Damage from PWN varies based on host species and environmental conditions – especially temperature and moisture. PWN causes rapid wilting and mortality in susceptible host trees, typically Pinus species exotic to the US, including Scots ( P. Pine wilt disease is a lethal wilting disease caused by the pine wilt nematode ( Bursaphelenchus xylophilus PWN). Best management practices include timely sanitation and chemical injections. The disease is now a threat in both eastern and western Colorado.High summer temperatures are required for the nematode to develop in the beetle and within infested trees.Some degree of resistance has been observed in native pines, however they may still be infected. Exotic pines including Scots, Austrian, and mugo are susceptible to infection by the nematode.Pine wilt is a lethal disease caused by a native nematode ( Bursaphelenchus xylophilus), vectored to trees by a wood borer insect–the pine sawyer beetle ( Monochamus spp.). ![]()
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