Identification

Historically, the identification of Armillaria was largely based on the morphology of the basidiocarp, and interfertility or mating compatibility. In recent decades, recognition and identification of Armillaria species has become increasingly reliant on DNA sequences, such as phylogenetic analyses representing multiple gene regions, which elucidate the evolutionary relationships among the species. 

Armillaria species are difficult to distinguish morphologically. In most cases, they are recognizable as distinct species: (a) they are intersterile; (b) there are some differences among them in morphology and molecular-genetic characters; (c) there are differences in distribution, host range, and virulence.

To confirm Armillaria root disease, the root collar and lower bole of the tree must be examined for those signs specific to the fungus or by culturing it onto agar from the host tissues. As with other diseases, early diagnosis is vital for successful control. Conventional identification techniques involve isolation of the fungus mycelium present and culturing on agar but this takes a longer time than for many other fungi hence the cultures are very prone to contamination. With the advent of the modern diagnostic techniques based on enzyme-linked immunosorbent assay (ELISA) and molecular methods based on nucleic acid, however, rapid identification of the disease has become possible.