This fungus survives on crop residue, stems and crown through the winter and summer in alfalfa stands and ooze spores during cool, wet weather – which occurred in Michigan this past fall and this spring.
Spring black stem is found early in the season and can reduce first cutting yields 40 to 60 percent in moderate to severely infected fields. Symptoms include black areas on the lower sections of the stem. Foliar lesions appear as small black spots.
Leaves become infected by spores splashed by the rain. Heavily infected leaves turn yellow and drop.
It is recommended to harvest heavily infected fields early to prevent both yield and quality losses from leaf drop. Scout fields weekly to determine the extent of the disease and make cutting decisions.
Click here to read the rest of the MSU Extension article, including research on treatment options.
Spring black stem is rarely a significant problem in new seedlings. Yield loss is due to stunted growth of infected plants and from stem death. The loss is likely only temporary as the alfalfa crown will put out new shoots.
However, the fungus may spread to the crown and cause crown rot, death of emerging seedlings, and root rot of mature plants if weather conditions are favorable (60 to 75 degrees Fahrenheit and damp).
After first cutting, the disease is rarely of significance, although the crown rot phase of the disease may continue to develop. FG
—From MSU Extension Field Crop Production Digest
PHOTO
Photo courtesy of MSU Extension.
