**Taxonomy:**
– Armillaria mellea was originally named Agaricus melleus by Martin Vahl in 1790.
– It was transferred to the genus Armillaria in 1871 by Paul Kummer.
– Subtaxa under A. mellea include var. radicata by Peck in 1891, var. viridiflava by Barla in 1887, and subspecies nipponica by J.Y.Cha & Igarashi in 1995.
**Description:**
– The basidiocarp has a smooth cap, often honey-colored, 3 to 15cm in diameter.
– The gills are white, sometimes turning pinkish-yellow with age.
– The stipe is up to about 20cm long, whitish at the upper end, and brownish-yellow below.
– The spores are elliptical, inamyloid, with a white spore print.
– The main part of the fungus is underground with black rhizomorphs.
**Hosts and Symptoms:**
– Armillaria mellea infects hardwood trees, conifers, and sometimes non-woody monocots.
– Signs include honey-colored mushrooms at the base of the infected plant, white mycelia, and black rhizomorphs under the bark and in the soil.
– Symptoms include slower growth, dieback of branches, yellowing foliage, and rotting wood.
– Leaf wilting, defoliation, and dieback occur after cambium destruction.
**Environment and Distribution:**
– A. mellea prefers moist soil and lower temperatures but can withstand extreme conditions.
– It is found in various landscapes like gardens, parks, vineyards, and natural areas.
– The fungus is widespread in northern temperate zones, found in North America, Europe, northern Asia, and South Africa, growing parasitically on broadleaf trees and fruits.
**Disease Cycle and Ecology:**
– A. mellea infects through basidiospores and rhizomorph penetration, with infection through basidiospores being rare.
– The fungus overwinters as rhizomorphs or mycelium, weakening infected wood due to decay after cambium destruction.
– Trees get infected when rhizomorphs invade the trunk, causing decay, growth reduction, and mortality.
**Management and Importance:**
– No known fungicides can kill Armillaria mellea after infection without damaging the plant.
– Practices to extend plant life include improving host condition through watering and fertilization.
– To prevent spread, regulate irrigation, remove stumps, and avoid physical root damage.
– Armillaria mellea is a common cause of death in trees and shrubs, causing substantial losses in natural and cultivated habitats.