Pre-emergent herbicides are those that prevent weeds from germinating. They are used to kill grass and broad-leaf weeds, but they do not kill plants that have already grown above the ground.
When applying pre-emergent herbicides in vegetable gardens, it's important to correctly identify the weeds you wish to control. Also, read labels carefully when selecting an herbicide. Some types kill vegetables and weeds alike, while others may not be effective against the weeds you are targeting. No one herbicide kills all weeds.
If you don't want to use chemicals in your garden, alternative control methods can be very effective, including pulling weeds by hand, shading, planting cover crops and mulching. When weeds sprout in your garden, remove them before they go to seed.
Avoid contact with skin and eyes when using herbicides, and wash exposed skin thoroughly following the application. Keep all chemicals in their original containers and store them where children cannot reach them.