Brown Spot Needle Blight of Pine
Scirrhia aecicola (Mycosphaerella dearnessii)
Distribution and Disease Cycle
This fungal disease attacks many species of pines, attacking developing, susceptible needles as they emerge in summer. Spores released from fruiting bodies on infected needles are spread by rain, animals or human activities to healthy current season needles where they germinate and enter needles through stomatal pores. Later in summer, new fruiting bodies are produced with mature spores that overwinter on infected or dead needles.
Symptoms and Signs
Yellow, water-soaked looking spots form on infected needles, eventually becoming brown with yellow borders or bands. In contrast to Lophodermium needle cast, which becomes evident in spring, lesions caused by brown spot needle blight do not usually appear until mid-late summer. Needles begin dying from the tips back until the needle is entirely brown, dropping in fall. Infections often begin on lower branches on the north side of the tree. In minor infections, needles will drop but buds can usually produce new foliage the following season; in more severe infections, entire branches can be killed.
If possible, remove and destroy infected branches, but do not prune trees during wet weather which can spread infection. Apply chlorothalonil as per label instructions beginning in spring when new shoot growth is 1-5 cm in length. Repeat applications at 3 to 4 week intervals during wet years or if infection is severe.
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