Symptoms andPhytophthoraspp. Associated with Root Rot and Stem Canker of Noble Fir Christmas Trees in the Pacific Northwest

Abstract

A survey of Noble fir Christmas tree plantations in Oregon and Washington was conducted to characterize symptoms and determine Phytophthora spp. associated with a root rot and stem canker disease. Symptoms were characterized and isolations were made from 158 symptomatic trees obtained from 30 plantations. The average root rot rating was 5.7 on a scale of 0-10. Approximately 74% of the trees exhibited branch flagging, and 82% had stem cankers that extended an average of 30.3 cm above the soil surface. Stem cankers originated from infected roots below ground and either extended straight up or spiraled up the stem as a narrow band of infected tissue. The average height of the trees was 77.5 cm. At least seven Phytophthora species were isolated from the roots and stems of the trees. P. cambivora, P. megasperma broad host range (BHR). P. cryptogea, and P. gonapodyides were the most prevalent species isolated. Other species included P. cactorum, P. citricola, and P. cinnamomi. This is the first paper reporting P. citricola and P. cambivora being found associated with stem cankering and root rot of Noble fir in the Pacific Northwest. All other species are known pathogens of Noble fir, but their ability to cause stem cankers and subsequent mortality, particularly in larger trees, after out-planting has not been demonstrated.