Hay harvested from a field where the stem nematode is known to occur should not be placed in pastures where alfalfa may be grown. Soil should be cleaned from farm machinery following their use in known infested fields. Other Clover Diseases Spring Blackstem Caused by Phoma trifolii Spring blackstem disease is devastating on red clover and also has been reported to occur on white clover. Forage yield, quality, and persistence can be reduced by spring blackstem. Blackstem is a slow-developing but persistent disease problem that contributes to the decline and death of clover stands.
Lesions are dark brown or black, and young stem lesions often have water-soaked borders.
Infections of leaves or stems generally progress slowly. Heavily infected leaves become yellow and fall. Young shoots and petioles may become girdled and die. This fungus survives around clover fields in plant debris and soil, and it can be seed-borne. Summer Blackstem Caused by Cercospora zebrina Summer blackstem occurs on crimson, alsike, and white clovers.