Identification and distribution of Armillaria species associated with an oak decline event in the Arkansas Ozarks

Abstract

Summary Forests in the Ozark Mountains of northern Arkansas recently experienced a widespread oak decline event. Armillaria, a root rot fungus, has been associated with other oak decline events and may have been an important contributing factor to tree mortality in this event. Although Armillaria has been identified from the Ozark Mountains in Missouri, it has never been investigated in the Arkansas Ozarks. Molecular diagnostic techniques were used in this study to identify species of Armillaria present on roots removed from dead trees of two common oak species, northern red oak, Quercus rubra L., and white oak, Q. alba L., from three geographic areas and on three topographic positions – ridges, south‐ and west‐facing benches. Armillaria(A. mellea, A. gallica or A. tabescens) was identified from 31% of root samples taken from 102 trees in seven of nine sample plots. Armillaria mellea, occurred most often (20 samples, both oak species on seven plots) followed by A. gallica (10 samples, northern red oak only on four plots), and A. tabescens occurred twice (on northern red oak in a single plot). Thus, all three Armillaria species occurred on northern red oaks while A. mellea was the only species recovered from white oaks. Results varied by topographic position with samples from tree roots on ridges having the fewest positive identifications, one of 29. West‐facing benches had the highest positive samples with 20 of 41 testing positive and trees on south‐facing benches were intermediate with 11 of 32 samples from infected trees. This study documents the occurrence of three species of Armillaria in the Arkansas Ozarks and their association with oak mortality resulting from an oak decline event coupled with a red oak borer, Enaphalodes rufulus, outbreak. Further, it documents some potential variation in host/pathogen combinations and forest site conditions.

Emergent insects, pathogens and drought shape changing patterns in oak decline in North America and Europe

“…The other common secondary agent in eastern North America, Armillaria spp. root rot, was present in many areas of the Ozarks that experienced decline (Bruhn et al, 2000;Kelley et al, 2009), but its relative contribution to oak mortality in the event remains unresolved. This situation provided a unique opportunity to study novel associations in a major episode of oak mortality, as well as an interesting setting in which to explore the potentially changing roles of forest history, drought, and insect outbreaks in oak decline.…”

Stand and individual tree characteristics associated with Enaphalodes rufulus (Haldeman) (Coleoptera: Cerambycidae) infestations within the Ozark and Ouachita National Forests

“…This is consistent with the fact that these trees did not contain more borer holes during the outbreak than live trees, yet they died anyway, presumably due to inferior capacity for resource acquisition and/or reduced resistance to E. rufulus or other secondary invaders, such as root pathogens (Armillaria spp). Three species of Armillaria infect Q. rubra and are widespread throughout the region (Bruhn et al, 2000;Kelley et al, 2009), yet their influence is unknown at these study sites.…”

Fine root dynamics of oak saplings in response to Phytophthora cinnamomi infection under different temperatures and durations

“…Oak decline in the eastern United States is most commonly reported in the south-eastern States, west to Missouri, and north into the mid-Atlantic region (Oak et al 2004;Fan et al 2008;Kabrick et al 2008;Kelley et al 2009;Fei et al 2011). In many of these reports, species within the red oak group (Quercus section Lobatae) were reported as being most commonly affected.…”