Dynamic and static weed control decision rules are derived analytically and compared. The dynamic rule leads to increased farm profits and greater control of weeds and weed seeds than the static rule, while total herbicide use is unchanged. The magnitude of the differences is estimated for atrazine control of foxtail and cocklebur in com production. Incorporating weed dynamics into weed control strategies increases farm profits between 1.0 and 1.4%. © 2001 Elsevier Science B.V. All rights reserved.