Widespread Occurrence of the Perfect Stage of Powdery Mildew Caused by \u3ci\u3eErysiphe polygoni\u3c/i\u3e on Sugar Beets in Nebraska

Powdery mildew, caused by Erysiphe polygoni DC (synonym E. betae [Vanha] Weltzien), has been a sporadic and relatively minor problem for sugar beet (Beta vulgaris L.) growers in western Nebraska. Yield losses in this region have been limited, in part because of the use of effective fungicides, but also because infection occurs late enough in the season that treatment has often been unnecessary. The perfect stage had been reported only once in the United States until 2001-2002 when it was identified from Idaho and Colorado (1). The teleomorph was also noted from several fields in Scotts Bluff County in Nebraska in October 2002. The first appearance of the disease in 2003 occurred during the second week of August within five miles of the fields where the perfect stage was noted in 2002. On the basis of these observations, a survey was conducted between mid-August and mid-October to map the appearance and distribution of the perfect stage of E. polygoni within the Nebraska Panhandle growing region. During this time, between 45 and 50 fields were surveyed in six Nebraska counties. This represented the majority (70%) of the sugar beet acreage in Nebraska. The first finding of the perfect stage occurred in early September from multiple fields in the vicinity of and including the field where the asexual stage was first reported in August 2003