Worms eating inside the stem are stalk borers. They feed on the tissue that carries water and nutrients between the roots and leaves. Sprays won't help once the insect is inside the stem. Remove and destroy infested stems. Fall clean up will also help reduce the occurrence of this insect. Several stem rots can also cause plants to wilt and die. Look at the base of the stem for blackening or a pinched appearance. This indicates a root or stem rot. Remove infected plants and wait several seasons before replanting lupines in this area. Amend heavy soils with organic matter before planting to reduce the risk of root rot. Lupines perform best in full sun, cool temperatures and well-drained soils for best results.