Phytophthora quercina is a papillate homothallic soil-borne plant pathogen causing root rot of oak tree species in Europe.

It also frequently presents sympodially branched primary hyphae, a high proportion of elongated, ellipsoid or ovoid oogonia, the absence of amphigynous antheridia.

[2] Its name derives from Greek Phytophthora φυτόν (phytón), “plant” and φθορά (phthorá), “destruction,” and quercina stems from the affected genus, Quercus.

The oogonia are spherical to ovoid in shape and come together with paragynous antheridia to form oospores that are globose during the sexual stage of the disease cycle.

[3] The oospores, mycelia, or chlamydospores will produce papillae sporangia that may vary in shape, including ovoid, globose, ampulliform, or peanut-shaped that dislodge easily from their sporangiophore.

[citation needed] Phytophthora quercina has a host range restricted to European oak tree species (Quercus spp.).

The host species affected are:[citation needed] These oak tree species are located within the known distribution range of P. quercina, which is currently reported only in Europe (Austria, Belgium, France, Germany, Hungary, Italy, Luxembourg, Netherlands, Serbia, Sweden, United Kingdom) and one country in Asia (Turkey).

The secondary symptoms occur above-ground and include leaf clusters, branch abscission, epicormic shoots, crown thinning, branch and crown dieback, reduced growth, chlorosis or wilted leaves, leaf and trunk necrosis, loose bark, and sapwood discoloration.