A multidisciplinary team of entomologists and plant pathologists led by Forest Service research entomologist Steve Seybold has discovered a new plant host for the organisms that cause thousand cankers disease. The disease has been characterized from walnut trees when the walnut twig beetle vectors a fungus, Geosmithia morbida Kola?ík, Freeland, Utley, and Tisserat (Ascomycota: Hypocreales), which colonizes and kills the phloem. Over the past two decades, thousand cankers disease has led to crown die back and the widespread mortality of Juglans tree species (walnut and butternut) in the U.S.. The team reported the occurrence of both the walnut twig beetle and G. morbida fungus in three wingnut species of walnut trees growing in the USDA National Clonal Germplasm Repository collection in northern California, and in the Los Angeles County Arboretum and Botanic Garden in southern California. Koch's postulates were satisfied with an isolate of G. morbida from the P. stenoptera species, confirming this fungus as the causal agent of thousand cankers disease in this host. A survey of the 37 Pterocarya Kunth accessions at the NCGR revealed that 46 percent of the trees had walnut twig beetle attacks or symptoms of G. morbida infection. This discovery suggests that the disease may threaten other tree species in the walnut family that may be of significance to urban forests.