Seasonal patterns of colonization of Norway spruce needles by Lophodermiumpiceae

Colonization of living Norway spruce needles by Lophodermium piceae was stu died in southern Sweden. One-month to 3-year-old needles were assessed for frequency of infection. Needles appearing the growing season of 1996 were m onitored and sampled at 1 to 4 week intervals over months. Infection freque ncy of the current-year needles increased from around 20% in July to approx imately 40% in August 1996. This level had then doubled to approximately 80 % after another growing season in August 1997. Multiple infections were rar e in the needles during the first growing season, but after the second grow ing season at least 70% of the needles had multiple infections. The average number of infections in 9-, 21- and 33-month-old needles were 1.3, 6.3 and 8.4, respectively. The size of the individual mycelia was estimated to be small in all needles, none of the individuals could be isolated from more t han two adjacent needle sections, about 1.5 mm long. In conclusion, the num ber of L piceae infections per needle increased during ageing of needles bu t mycelial growth is probably postponed until needle senescence and death.