Importance of using pre-emergents
Due to the increasing increase in resistance and tolerance of weeds to the molecules of some herbicides, alternatives for their control have been necessary, as post-emergent herbicides have not been efficient in controlling some species, such as ryegrass, horseweed and turnip in wheat cultivation. Therefore, the application of pre-emergent herbicides has been recommended, an essential practice, carried out before the emergence of weeds and crops.
Pre-emergents, as they have residual action in the soil, act by reducing the germination and emergence of weed plants in the crop, thus reducing the soil seed bank, enabling the crop to develop before weed competition begins. In this sense, it is also important to pay attention to the diversification of active ingredients, to delay the evolution of selection of resistant species.
This management approach reduces the initial competition between the crop and the weed, causing the agricultural crop to grow “cleanly”, giving less opportunity for invasive plants to develop. The practice also favors post-emergence management, as the producer will possibly not need to make as many applications after establishing the crop, helping with operational gains.
Ideal conditions for application
Currently, there is a registry of pre-emergent herbicides with different mechanisms of action, which differ from the post-emergent ones used, and a rotation plan of the chemical groups available for control can be created.
Trifluralin is an example of a selective pre-emergent herbicide, which has an effect on broadleaf and narrowleaf weeds. Its application is recommended under environmental conditions of at least 55% air humidity and an ideal temperature of 20 ºC to 30 °C. In wheat cultivation, it is mainly indicated for ryegrass control. Its application is recommended immediately after planting the crop or within a maximum of 3 days afterwards, without incorporation, during a period in which the seeds of the invasive plants and the crop have not yet germinated.
