Heavy stubble may hold herbicide away from the soil until adequate rainfall washes it onto the soil. If the stubble has not been grazed, and is still standing upright, it may be possible to spray before seeding with the spray set absolutely vertical so that the chemical falls directly onto the soil. There should be no wind. It is also possible to spray during rain, which gives the chemical a better chance of reaching the ground. 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.