Studies suggest that emergence of weed seedlings can be diminished by decreasing the exposure of seeds to light during tillage. Field studies conducted near Ames, Iowa, tested the effect of excluding light during tillage on emergence of common weed species of central Iowa. Plots were tilled Botany either during the day, during the day with implements covered, at night, or at night with implements covered, and subsequent seed emergence was monitored. The effect of brief exposure to light on germination of weed seeds under controlled laboratory conditions was also studied.