In Zielonka Forest District seven Scots pine plantations monitored in 1998-2001 for Armillaria ostoyae and Heterobasidion annosum disease development proved affected mainly by the former pathogen. Observations of 200 trees per plantation (every spring and fall) showed there was no correlation between the morphological features and over ground symptoms and infestation of pines by the pathogens in question and mortality of trees. The young stands were threatened more by Armillaria than by Heterobasidion annosum s.s., yet the infestation by Armillaria decreased with age of trees while the infestation by Heterobasidion increased.

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