Section outline
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Disease symptoms vary depending on the host tree, with more severe symptoms occurring in the lower parts of the crown and then progressing upwards in the trees (Sinclair and Lyon, 2005; Skilling and Nicholls, 1974).
At the beginning of infection, a small yellow, sometimes light grey‐green or reddish brown, irregular circular spot, with defined margins, appears on the needles (Hedgcock, 1929). As the infection matures, the yellow spots soon become brown, resin‐soaked (depending on the host), and framed with yellow edges like a halo (Skilling and Nicholls, 1974). It might happen that the symptoms appear only as chlorosis without bands, for example on P. strobus (Broders and kt., 2015). Dark, subcuticular fruiting structures (acervuli) develop, releasing olivaceous, cylindrical, curved or straight conidia with 0-6 septa, rounded apex and truncate base, often with oil droplets, size ca. 30 x 4 µm (Jurc and Jurc, 2010; Tubby et al., 2023). The needles begin to die from the top towards the base before eventually shedding from the trees (Hedgcock, 1929; Skilling and Nicholls, 1974). Usually, only second and third-year needles are affected, leaving healthy new growth at the branch tips. New growth tips are infected through the inoculum on the old needles the following season. (Skilling and Nicholls, 1974).
L. acicola symptoms are easily confused with those caused by Dothistroma septosporum and D. pini (Barnes et al., 2004, 2016). Therefore, microscopic, and molecular diagnostics are important for accurate identification.
