BACK

Occurrence of stem canker on soybeans in South Dakota. T. E. CHASE and C. Tande. Plant Science Department, South Dakota State University, Brookings, SD 57007. Phytopathology 91:S15. Publication no. P-2001-0105-AMA.

Severe levels of disease were observed in soybean fields at mid reproductive stages in South Dakota during 1998 and 1999. Entire fields underwent a rapid shift from apparently healthy to 30-50% mortality over a one-week to ten-day period. Symptoms included wilting, dead stems, poor pod fill, and cankers at the lower nodes. A survey was conducted in 2000 and identified additional fields with high levels of disease. Most fields involved were planted in narrow rows, had high plant populations and were under reduced tillage. Isolates established from canker margins were inoculated to toothpick/water agar and produced perithecia consistent with published descriptions of Diaporthe phaseolorum var. caulivora. The disease has been tentatively identified as Northern stem canker. Severe epiphytotics of this disease have not been observed in South Dakota in recent years prior to 1998, and the reasons for this are not clear. Investigations of environmental factors and agronomic practices associated with outbreaks of stem canker are being conducted. We are also assessing molecular and pathogenic variability of the pathogen.