Septoria leaf spot: biology
Septoria leaf spot (Septoria spp.) causes leaf discolouration, leaf drop, reduced fruit bud production and lower yields.
In the sprout year, spore release from overwintered and diseased fallen leaves occurs intensively, beginning in late May in response to rain. Tiny water-soaked spots begin to appear on infected leaves 10 to 14 days after infection, but are not visible to the naked eye until after about four weeks. Lesions spread and expand – by mid- to late July, severely diseased leaves begin to drop. Although stems may have become infected, stem cankers do not develop until spring of the fruit year.
In the fruit year, spore release from overwintered leaves mostly occurs during the bloom period. Release of spores from pycnidia in infected leaves and stem cankers occurs when it rains, and spores are splashed onto the foliage. By mid- to late July, severely diseased leaves begin to drop. In general, prolonged wet weather in June favours spore release and infection, while subsequent prolonged, hot, dry weather causing moisture stress during July and August promotes drop of infected leaves and fruit.
