Distribution and frequency of Cronartium flaccidum on Melampyrum spp. in Finland

Distribution and frequency of Cronartium flaccidum telia were investigated on Melampyrum spp. growing wild in 355 Scots pine stands in Finland. Telia were found for the first time on M. arvense in Finland and for the first time on M. pratense and M. nemorosum in natural forests anywhere. Cronartium flaccidum telia were found in 22% of all stands with M. sylvaticum, 3% of stands with M. pratense, 12% of stands with M. nemorosum, 100% of stands with M. arvense, and 0% of stands with M. cristatum. Melampyrum spp. with telia were mostly found in northern Finland. The proportions of stands with telia and of plants with telia per stand, the frequency of telia-bearing leaves per plant, and the average number of telia per leaf were greater for M. sylvaticum than for most of the other Melampyrum species. In severely affected pine stands, telia were frequent on M. sylvaticum, but scarce or lacking on M. pratense. On sites with M. sylvaticum, the respective proportion of telia-bearing plants was significantly higher in young development classes and severely diseased stands than in older development classes and slightly damaged stands. The results suggest that the main host of C. flaccidum is M. sylvaticum in northern Finland.