First Report of Sirococcus clavigignenti-juglandacearum on Black Walnut.

Sirococcus clavigignenti-juglandacearum is killing butternut (Juglans cinerea) throughout North America. Although black walnut (J. nigra) and other Juglans spp. can be infected with artificial inoculations (2), butternut previously was thought to be the only known natural host. In May 1985, a black walnut, 48 cm in diameter with multiple elliptical cankers on the main stem and lower branches, was found by R. L. Anderson in North Carolina. No fruit bodies were present but isolation from cankers characteristic of those found on butternut produced sporulating pure cultures identical to those described for S. clavigignenti-jugland-acearum (1). A large butternut with coalescing, elliptical cankers was located about 45 m from the infected walnut. In spring 1996, in a plantation in southeastern Minnesota, examination of two 20-year-old black walnuts exhibiting branch dieback revealed hyphal pegs and hyaline, two-celled, fusiform conidia identical to those described for S. clavi-gignenti-juglandacearum (1) on 1994 and 1995 branch wood. Isolations from symptomatic twigs resulted in recovery of the fungus in pure culture. Scattered, naturally occurring, infected, mature butternut and butternut saplings with multiple branch and stem cankers were growing throughout the plantation. Severe winter injury of black walnut in southeastern Minnesota the preceding 3 years may have predisposed trees to infection. References: (1) V. M. G. Nair et al. Mycologia 71:641, 1979. (2) M. E. Ostry et al. Gen. Tech. Rep. NC-165, St. Paul, MN: USDA, Forest Service, North Central For. Exp. Stn., 1994.