A mixture of activated carbon and vermiculite was used to increase the tolerance to 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) of direct-seeded cucumbers (Cucumis sativus L., var. Wisconsin SMR-15) in greenhouse tests and direct-seeded tomatoes (Lycopersicum esculentum Mill, var. Bouncer) in greenhouse and field (var. Heinz 1370) tests. The tolerance of cucumbers to dimethyl tetrachloroterephthalate (DCPA) and 4-(methylsulfonyl)-2,6-dini tro-N,N-dipropylaniline (nitralin) also was increased in field trials. When the mixture was placed in a hole (0.75 inch deep by 1 inch diam) over the crop seed to the level of the soil surface, preemergence herbicides were detoxified in the small area; and the crop plant was not injured. The herbicide remained active outside the small protected area. Also, a wafer consisting of an activated carbon-vermiculite mixture, fertilizer, and seed provided protection to direct-seeded crops.