Soil Herbicides

Soil-applied herbicides are effective against germinating seeds or young seedlings. To function, they must persist in the soil during the time when the weed seeds are germinating. After this point, they will have little effect on the plant.

As long as growing conditions are favorable for weed growth, you should expect good control with soil-applied herbicides. Herbicide activity in the soil is influenced by the soil texture, organic matter content, acidity, and moisture conditions, all of which are also factors necessary for optimum plant growth. High temperatures and moist soils also favor the decomposition of herbicides in the soil. Microorganisms and chemical reactions in the soil also aid in the decomposition process, which prevents herbicide buildup in the soil.

Some chemicals used for long-term weed control, however, may last for two or more years in the soil. When seasonal weed control is needed among desirable plants, chemicals that remain in the soil only a few days to a few weeks can be used. Some chemicals, however, may remain in the soil in sufficient amounts to affect susceptible crops the following season.