ARMILLARIA ROOT AND CROWN ROT

Armillaria root and crown rot (also known as oak root rot) is a major cause of premature tree death in southeastern stone fruit orchards. In addition, the persistence of the causal agent on root pieces in the soil frequently prevents the establishment of new orchards in previously infested sites. Two species in the fungal genus Armillaria, A. tabescens (Scop.)Dennis et al. (= Clitocybe tabescens (Scop.) Bres.) and A. mellea (Vahl.:Fr.) P. Kumm., can cause the disease in the Southeast. Although the two species are generally very similar, there are a few features that distinguish them. The mushrooms (basidiocarps) of A. tabescens (Figure 1A) lack an annulus or ring just below the cap and can be a darker shade of brown than those of A. mellea (Figure 1B). In contrast, an annulus is present in the basidiocarps of A. mellea and, in some cases, rhizomorphs (shoestring-like networks of condensed, black hyphae) may be produced from host tissues infected by this species (Figure 2). Although there is evidence that A. mellea is more aggressive than A. tabescens, little is known about the relative importance of the two species and their roles in Armillaria root disease in southeastern peach production systems. However, basidiocarps of A. tabescens are more commonly found in orchards than those of A. mellea