Diseases Sweetclover may be attacked by a number of diseases including damping-off, root rot and crown rot, stem rots and leaf diseases. The incidence of these diseases is usually light on forage stands and slightly heavier on seed stands. While these diseases damage the plant and negatively influence productivity, they are not normally considered a serious problem. The sweetclover weevil is this crop's main pest. The weevil chews the leaves of seedlings or second-year stands in the spring and, to a lesser extent, in late summer.
Damage is likely to be most severe in years when growth is slow.
Seedling stands may be completely destroyed, but because plants in second-year stands are growing more vigorously, damage is usually minimal. The weevil can be controlled through the use of insecticides, by tilling of second-year fields as soon as harvested, and by locating new stands as far as possible from established fields of sweetclover. Damage to seedling stands may also occur from cutworms and grasshoppers. Cutworm damage is indicated when seedlings wilt and die because they have been cut off at or below ground level, or when the entire above ground portion of the plant is eaten. Grasshopper damage is severe when infestations are heavy.