A harrowing or rotary hoeing can help incorporate herbicides and remove escaped weeds where adequate rainfall has not occurred. Post emerge herbicides perform best when weeds are actively growing. High temperature, high relative humidity and adequate soil moisture are ideal. Drought stress of weeds reduces herbicide effectiveness. Weeds are not able to grow as rapidly with limited moisture.
Herbicides affect processes that occur when the plant grows.
Weeds develop a thicker wax layer, or cuticle, on their leaves to help reduce moisture loss during dry conditions. This can reduce the ability of post emerge herbicides to enter weed leaves. Common lambsquarters are especially effective at developing thick cuticles and therefore difficult to control. Herbicide adjuvants help overcome the weed leaf's resistance to herbicide penetration. The selection of the proper adjuvant can improve weed control under drought stress conditions.