Biology and management Wild proso millet mimics sweet corn growth. Seeds mature before corn harvest, facilitating spread with machinery. Seed longevity in soil, however, is relatively short (3 to 5 years). Rotating to grass seed or summer annual broadleaf crops helps deplete the seedbank if wild proso millet is not allowed to produce seed. Wild proso millet seedlings emerge erratically throughout the season because of inherent seed dormancy, which is strongest for black-seed types.