Armillaria mellea can infect the perennial weed, Rumex obtusifolius, in the UK

Armillaria mellea is a common pathogen of trees, woody shrubs and some herbaceous plants, causing root, root-collar and butt rot (Fox, 2000). On examination of a wilted broad-leaved dock (Rumex obtusifolius), growing on the edge of woodland, near Reading, UK, in 1994, the main root and root-collar region was found to be colonised with mycelial fans, typical of Armillaria mellea. Rhizomorphs were found in the soil adjacent to the plant. The mycelium was isolated onto Malt Extract Agar and its identity was confirmed to be Armillaria mellea.

To fulfil Koch's postulates, ten potted dock plants were each inoculated with an isolate of Armillaria mellea by placing colonised sections of hazel (Corylus avellana) branch (≈6cm long by 2.5cm in diameter; West, 2000) adjacent to the tap root of the plants. Additionally an isolate of Armillaria ostoyae, which is a serious pathogen of coniferous trees, was tested against ten similar plants. After 7 months, the foliage of most plants (7 out of ten, for both isolates) was observed to be wilted or senesced. Examination of the roots and collar region of these plants showed extensive rotting and fans of white mycelium confirming infection by Armillaria. All other plants also had infected roots, but as the infection had not yet reached the root collar, the foliage had not been affected.

A. mellea and A. ostoyae were also found to infect artificially inoculated docks in field conditions.

Broad-leaved dock is a common perennial weed of short-term leys and permanent pastureland. Salmon (1923) had noticed that "Armillaria mellea" (at that time "sensu lato" - which in Britain was a complex of several species) spread from an apple tree to brambles (Rubus sp.) and docks (Rumex sp.) but the species of dock was unknown and it was not reported whether the docks were killed. Our study confirms that there is potential for docks to assist the vegetative spread of both Armillaria mellea and Armillaria ostoyae across pasture or other treeless habitats and into woodlands in a similar way to that proposed for Epilobium angustifolium by Klein-Gebbinck et al. (1993).