Management

• Physical removal of inoculum: by removing diseased trees and uprooting even neighbouring uninfected stumps. For example, trenches over a metre deep are dug to isolate the infected plants from healthy parts of a vineyard or a fruit orchard have been used to control spread of Armillaria root disease. Laying a plastic barrier in a trench and then backfilling it with the removed soil has been used for controlling the disease in kiwifruit orchards. Complete eradication of the fungus is also improbable and of doubtful value, and reinvasion by the fungus is possible. Soil disturbance may also stimulate fresh rhizomorph production, increasing the risk of disease to newly planted trees. Excessive removal of woody debris from a soil may be detrimental to antagonistic mycorrhizas.  

• Stump removal: the most effective means of controlling the disease is to remove all sources of infection from the site. This normally means removing infected stumps and plants. The fungus may be present as rhizomorphs or minor root infections among trees and shrubs even where there is no sign of disease above ground. Therefore, if woody plants are removed for any reason, it is better to uproot them than to leave stumps in which the fungus could build up and become a greater threat to surrounding plants. If neither stump removal nor prevention of rhizomorph spread is possible, the only alternative is to leave stumps and infected trees where they are, accepting the inevitable losses, and to replant gradually with resistant species. 

• Reducing root disease susceptibility: Because Armillaria seems to attack trees that are stressed due to climate maladaptation or other stress factors, a primary strategy for managing Armillaria root disease is to plant, select, or naturally regenerate trees that are well-adapted to the site and exhibit adaptation to a broad range of environments. Following a rotation with resistant species, the pathogen should have died out in the old root systems, permitting the reestablishment of susceptible species. In some situations, planted trees appear more susceptible to Armillaria root disease than naturally regenerated trees, especially if planted trees are not adapted to the site. Care must also be taken to avoid wounding trees that remain after thinning and use other methods to increase host vigor. In some horticultural situations, Armillaria-resistant rootstock may be available. Under horticultural conditions, the removal of soil surrounding the root crown may offer protection against Armillaria.

• Chemical treatments and fumigation: The most effective chemicals against A. mellea in vitro on 3% Malt Extract Agar were hexaconazole and flutriafol (both triazoles), fenpropidin (a piperidine), guazatine (a guanide) and phenylphenol (a phenolic compound) with Bray’s Emulsion as a standard.Volatile, toxic chemicals are placed in a hole drilled into an infested stump. The chemical kills the fungus or weakens it to the point other fungi can kill it. Even where stump extraction is effective at reducing Armillaria root disease, considerations should be given to (1) disturbances may allow new Armillaria inoculum to become established, (2) cost effectiveness, and (3) deleterious ecological consequences, such as reduced organic compounds/nutrients, soil erosion, and other long-term effects of mechanical disturbances. Still, chemicals for controlling Armillaria are either ineffective or are phytotoxic or have other environmental consequences, therefore is a need for biological control.

• Biological control: Antagonistic organisms might not be able to prevent Armillaria from becoming established in stumps, but they may restrict further stump colonisation and thus limit the available food base. An economical and environmentally friendly approach to biological control is the use of management practices to favor native, in situ biological control agents [e.g., Trichoderma spp. (fungi) and Pseudomonas (bacteria)] that are already present on the site, while discouraging the Armillaria pathogen. Among the most thoroughly studied fungal antagonists of Armillaria are Trichoderma species, common fungal hyperparasites abundant in the majority of soils.  Mycophagous nematodes have also been implicated in the biological control of Armillaria. Studies in vitro have shown that ectomycorrhizal fungi can inhibit the growth of Armillaria. However, direct protection by mycorrhizas seems unlikely as the main infection sites for Armillaria are on larger roots rather than the fine roots where mycorrhizas develop.

Using management practices to favor native, in situ biological control agents does not require regulatory approval, and it focuses on the native biological control agents that are already adapted to the site. Methods, such as metagenomics and metabarcoding, can be used to determine fungi and bacteria present in the forest soil; however, knowledge of the microbiome and associated analyses are needed to determine which treatments (e.g., applications to adjust soil organic matter, N, and pH, and/or prescribed fire) favor the biological control agents and discourage the Armillaria pathogen.

Management of Armillaria root disease should focus on: (1) selecting or planting site-adapted tree/shrub species with less susceptibility to Armillaria, (2) using silvicultural methods to reduce tree stress, such as increasing tree spacing, (3) reducing inoculum of pathogenic Armillaria, (4) implementing management practices that favor natural biological control agents of Armillaria, (5) selecting or planting trees adapted to climate change and Armillaria root disease