Editing Armillaria (section)

== Pathology ==
{{Main|Armillaria root rot}}

Honey fungus is a white-rot fungus, which is a [[pathogen]]ic organism that affects trees, [[shrub]]s, woody climbers and rarely, woody herbaceous [[perennial]] plants. Honey fungus can grow on living, decaying, and also dead plant material (being a [[facultative saprophyte]]). This means it can kill its host with little consequence, unlike [[parasite]]s that must moderate their growth to avoid host death.{{r|si}}

Honey fungus spreads from living trees, dead and live roots and stumps by means of reddish-brown to black [[rhizomorph]]s (root-like structures) at the rate of approximately {{convert|1|m|ft|order=flip}} a year, but infection by root contact is possible. Infection by spores is rare. Rhizomorphs grow close to the [[soil]] surface (in the top {{convert|20|cm|in|order=flip}}) and invade new roots, or the root collar (where the roots meet the stem) of plants. An infected tree will die once the fungus has [[girdling|girdled]] it, or when significant root damage has occurred. Additionally, Infections can occur through the activity of wood boring beetles. For example, ''[[Agrilus biguttatus]]'' most commonly girdle in [[Oak|oak trees]], which allows fungi to grow in the stems of these infected trees. This can happen rapidly, or may take several years. Infected plants will deteriorate, although may exhibit prolific flower or fruit production shortly before death.{{why|date=March 2023}}
[[File:Mycelial cord Armillaria (rhizomorphs).jpg|thumb|[[Mycelial cords]] ''Armillaria'']]
Initial symptoms of honey fungus infection include [[Forest dieback|dieback]] or shortage of leaves in spring. Rhizomorphs (also called mycelial cords) appear under the [[bark (botany)|bark]] and around the tree, and mushrooms grow in clusters from the infected plant in autumn and die back after the first frost. However these [[Symptom#Symptom versus sign|symptoms and signs]] do not necessarily mean that the pathogenic strains of honey fungus are the cause, so other identification methods are advised before diagnosis. Thin sheets of cream colored mycelium, beneath the bark at the base of the trunk or stem indicated that honey fungus is likely the pathogen. It will give off a strong mushroom scent and the mushrooms sometimes extend upward. On [[conifers]] honey fungus often exudes a gum or [[resin]] from cracks in the bark.

=== Hosts ===
Potential [[Host (biology)|hosts]] include [[Pinophyta|conifers]] and various [[monocotyledon]]ous and [[dicotyledon]]ous trees, [[shrub]]s, and herbaceous species, ranging from asparagus and strawberry to large forest trees (Patton and Vasquez Bravo 1967).<ref name="patton">Patton, R. F.; Vasquez Bravo, R. 1967. "Armillaria root rot ''Armillaria mellea'' (Vahl ex Fr.) Kummer".  p. 37–38 in Davidson, A. G.; Prentice, R. M. (compilers and eds.). ''Important forest insects and diseases of mutual concern to Canada, the United States, and Mexico''. Canadian Department for Rural Development, Ottawa, Ontario, Pub. 1180.</ref> ''Armillaria'' root rot enters hosts through the roots. In Alberta, 75% of trap logs (Mallett and Hiratsuka 1985)<ref name="mall3">{{cite journal |last1=Mallett |first1=K. I. |last2=Hiratsuka |first2=Y. |year=1985 |title=The 'trap-log' method to survey the distribution of ''Armillaria mellea'' in forest soils |journal=Canadian Journal of Forest Research |volume=15 |issue=6 |pages=1191–1193 |doi=10.1139/x85-195}}</ref> inserted into the soil between planted spruce became infected with the distinctive white mycelium of ''Armillaria'' within one year. Of the infestations, 12% were ''A. ostoyae'', and 88% were ''A. sinapina'' (Blenis et al. 1995).<ref name="blen">Blenis, P.; Titus, S.; Mallet, K. 1995. "Impact of Armillaria root rot in intensively managed white spruce/asspen stands". Natural Resources Canada/Alberta Land and Forest Service, Edmonton, Alberta, Canada/Alberta Forest Resource Development Agreement (FRDA), Project A5023-129 Rep. 5 p.</ref> Reviews of the biology, diversity, pathology, and control of ''Armillaria'' in Fox (2000)<ref name="fox">Fox, R. T. V. (2000). "''Armillaria'' Root Rot: Biology and Control of Honey Fungus". ''Intercept'', Andover, Hants., England. 222 p.</ref> are useful.