Survival of Cercospora sojina on Soybean Leaf Debris in Illinois

Abstract

Historically, frogeye leaf spot (FLS, caused by Cercospora sojina) of soybean has been observed more frequently in the southern United States than the north-central United States. However, in recent years, FLS field observations have increased in the north-central United States. To better understand the survival rate of C. sojina in Illinois, a field study was conducted at three locations: Monmouth (west-central Illinois), Urbana (east-central Illinois), and Dixon Springs (southeastern Illinois). At each location, soybean leaves affected by FLS were placed at depths of 0, 10, and 20 cm and retrieved at different durations up to 24 months. To determine the viability of C. sojina in the collected leaves, a greenhouse bioassay was used. Survival of C. sojina declined equally with time at all three locations through 19 months. After 24 months, C. sojina from leaves that had been placed at Monmouth and Urbana were no longer viable, whereas leaves that had been placed at Dixon Springs produced viable inoculum. Depth of leaf placement had no effect on survival of C. sojina at any of the locations. These results suggest that planting a nonhost crop for two years in central Illinois will reduce levels of C. sojina inoculum to a negligible amount; however, soybean farmers in southern Illinois may need a longer rotation for FLS management. Accepted 10 May 2014. Published 23 July 2014.