However, if there is a heavy covering of stubble, it may shield the weeds from the herbicide, making it necessary to wait until the weeds have grown above the stubble before spraying. Complete control is then much less likely to result. Rates should not be reduced below the minimum recommended, and in most cases should be kept up to the maximum. In some situations, such as the use of diclofop for ryegrass control in wheat, full control of the larger weeds cannot be achieved. As the no-till system leaves most such seeds on the surface, an extra measure of control may be possible in this way.
More research is needed, however, before firm recommendations can be made.
When fully incorporated, they will shorten the shoots of buried seeds so that they fail to reach the surface, or they will prevent root development in surface seeds, so the weed cannot reach moisture and soon dies. When left on the surface these herbicides cannot do this. Roots that enter the soil will escape the chemical and can continue growing, and shoots emerge straight into the air. The weed may suffer a slight check, but will usually survive. The compounds in this group are also quite volatile.