Herbicides can be applied by several methods and at various times during the year. The following terms may be found on herbicide labels pertaining to their use.
Herbicides in this group must be mixed into the surface soil before planting in order to achieve good weed control. Usually, herbicides that must be incorporated in the soil are highly volatile. Without incorporation, these herbicides would be lost into the air as a gas. Read and follow the herbicide label for specific instructions regarding incorporation. Examples of PPI herbicides are Treflan, Sutan+ and Fradicane Extra.
Herbicides in this group are usually applied immediately after planting. Preemergence means that the herbicide is applied after the crop seeds are planted but before the crop and weeds have emerged from the soil. This group of herbicides usually needs a rain within a few days after application to move the herbicide from the soil surface down into the top layer of the soil where most weed seeds are located. Some typical herbicides are Lasso, Dual, Lorox, AAtrex and Bladex.
This is a combination of the two types of application already discussed. A preplant incorporated herbicide is applied, the crop planted, and a preemergence herbicide is then applied. This practice is used to achieve a broader spectrum of weed control.
The application of herbicides mixed together in the sprayer tank is a common practice. Herbicides are also applied in combination with liquid fertilizer. When mixing herbicides or other pesticides in the spray tank, be certain to follow label recommendations and precautions. Specific directions for tank mixing of herbicides are frequently listed on the label.
This group of herbicides is applied after the weeds and crop have emerged from the soil. These treatments can be applied in either a broadcast or directed fashion. When applying postemergence herbicides, it is necessary to have maximum coverage of the weed with the spray solution. Surfactants are often used with postemergence herbicides to enhance control. For specific gallonages required and the amount, if any, of surfactant required, consult the label.
This type of postemergence application of herbicides is based upon a height differential between weeds and the crop. The herbicide is usually directed away from the crop and onto the weeds. For example, when the weeds extend above the soybean canopy Roundup can be applied with a rope wick or other wiper type applicators.