Two common types of post-emergence herbicides are Glyphosate and Paraquat. Glyphosate (e.g. Round-up, Sunphosate, Sarosate) is usually strictly applied 1-2 weeks before planting, whereas Paraquat (e.g. Gramazone) can be mixed with Pendimenthalin at the recommended rate and applied immediately after planting. Paraquat kills any live weeds in the field whereas Pendimenthalin kills pre-emerging weeds. Also, selective pre-emergence herbicides like Atrazine can be applied at the recommended rate 2-3 days after planting. Pre-emergence herbicides should always be applied before maize and weed seedlings emerge. The effectiveness of the herbicides is enhanced by very good land preparation. Moisture is required for activation of the herbicide. Herbicides give good control of annual grasses and broadleaf weeds but usually need to be supplemented by hoe weeding to control perennial weeds or weeds emerging after the herbicides have dissipated.
Successful use of herbicides depends on proper calibration of sprayer, quantity of herbicide to be used, method and time of application, climatic conditions, type of weeds etc. For best weed control and maximum grain yields, use integrated weed management strategies that combine mechanical, chemical and cultural methods.