Section 3: Types of Herbicides
Anchor: #i1022178Soil-Active (Residual) Herbicides
Residual herbicides remain active within the soil for a period of time and prevent germination of seeds and growth of roots. Residual herbicides are moved into the root zone by water and rainfall. The herbicide is absorbed by the plant’s root system and distributed (translocated) throughout the plant. Plant growth processes are then affected. Toxic symptoms should begin to appear within several days.
The rate at which toxic symptoms begin to exhibit within the plant varies with the type of soil, rainfall rates, plant species and the rate of herbicide applied. Residual herbicides can be applied to the soil in the winter months prior to the initial emergence of new growth in the early spring, or shortly thereafter.
CAUTION: Residual herbicides should never be applied to bare ground. Vegetation should always be present before applying residual herbicides.
Figure 3-5. Outrider® herbicide.
Figure 3-6. Escort® XP herbicide.
Figure 3-7. Landmark® XP herbicide.
Anchor: #i1022230Foliar-Applied Herbicides
Foliar-applied herbicides, as the name implies, must be applied to the green and growing foliage of the target species to be effective.
The herbicide is absorbed through the foliage and transported (translocated) throughout the plant and stored in the root system. Several days are typically required before the toxic affects of the herbicide appear. Repeat application of foliar-applied herbicides may be necessary, as most foliar-applied herbicides used by TxDOT do not have any soil residual activity.
Additionally, certain plant species may be resistant to the herbicide, requiring either additional applications or the use of more than one chemical in combination if broad-spectrum control is required.
Figure 3-8. Roundup Pro® herbicide.
Figure 3-9. Transline® herbicide.
Figure 3-10. Pathfinder II® herbicide.