Management

Detection

Apart of detection based on visible symptoms, fruiting structures and spores, L. acicola can be identified via isolation to pure culture. It can be isolated on Malt Extract Agar from symptomatic needles following surface sterilization. Firstly, a white aerial mycelium appears which turns greenish olive to dark olive, forming stromatic and erumpent colonies producing an olive-green conidial slime. At 20°C in daylight, the mycelium grows 2.5–3 mm a week. Colonies produce a yellow diffusate (EPPO, 2015).

L. acicola can be detected by methods of molecular biology. Probably the most used protocol applies real-time quantitative PCR with hydrolysis probes and detects simultaneously Dothistroma septosporum, D. pini and L. acicola. The amplified target gene of L. acicola is a single-copy gene Translation Elongation Factor I alpha (Ioos et al. 2010). This assay has been developed to detect the pathogen directly from the needles. Conventional PCR test (Ioos et al. 2010) with lower sensitivity can be used as well and it is sufficient for DNA extracted from a pure culture.

Another possibility of a sensitive molecular in planta detection and identification of L. acicola is an assay developed primarily for outdoor use, without using an expensive laboratory equipment. It is based on a Loop-mediated Isothermal Amplification (LAMP) and it was designed and validated by Aglietti et al. (2021).

Aerobiological monitoring of L. acicola inoculum must be based on the fact that conidia (majority of L. acicola propagules) are mostly transported via droplets of water. Therefore, the distance they are able to travel is rather short and higher concentrations can be expected only bellow infected branches. However, Wyka et al. (2018) observed conidia during some samplings even 60.6 m far from the source. These authors were sampling the conidia with passive spore traps made of microscopic slides covered by petroleum jelly and evaluated the samples microscopically.  

Preventive measures and suppression measures

The most effective measures to avoid infection with L. acicola are to use healthy seedlings (Cordell et al., 1990; Skilling and Nicholls, 1974) and to plant in areas away from previously infected plantations that serve as a reservoir of infection (Tainter and Baker, 1996). Thinning is recommended as a preventive measure against L. acicola in natural pine stands (McIntire et al., 2018). Pruning is not recommended during rainy or wet periods due to the increased risk of infection (Skilling and Nicholls, 1974). When performing pruning, it is necessary to disinfect and clean all tools after each use (Kais, 1978).

Winter burning every 3 years can be used to protect P. palustris from L. acicola infection. For other Pinus spp., controlled burning depends on tolerance to fire damage (Siggers, 1932). When the disease is detected, especially in regions and countries where L. acicola is a quarantine organism, it is suggested to completely eradicate the diseased trees or stands (Pehl and Cech, 2008).