Desiccating weeds to prepare the area for new cultivation is a fundamental procedure for the success of a crop. This herbicide management aims to eliminate these already established invaders, avoiding losses to the crop in succession due to competition for water, light and nutrients, as well as facilitating the implementation of the crop.
There are numerous advantages of desiccating weeds, especially when we talk about pre-sowing desiccation. One of the bottlenecks of this management is the so-called “clean sowing”, where the crop of economic interest, as a result of desiccation, is implemented in adequate sowing conditions, facilitating both the operation and the establishment, which, due to no initial competition with weeds, it can express its potential at the initial start of the crop.
Strategies for managing desiccation
One of the alternatives when working with desiccation of specific plants is the use of sequential applications of herbicides, with a pre-determined time interval between applications. This technique makes it possible to eliminate several emergence flows of apparent plants before the emergence of the main crop, allowing more efficient control with the application of herbicides with different active ingredients, increasing the control spectrum of specific plants and delaying cases of herbicide resistance.
When to opt for a sequential application?
Although this technique presents a broad advantage in controlling specific plants, there are some points that must be analyzed to ensure that it is the best management option.
As it involves more than one input of herbicides in the workforce, it becomes a management that involves a high investment for the producer, with herbicides, machinery and labor. Sequential application requires greater planning, where it is necessary to identify the planned plants and position the best herbicides. It is also important to be careful with the window between applications, which may be affected by adverse weather conditions. This delay can compromise control efficiency or even cause delays in harvesting, as many of the herbicides used have a waiting period to avoid phytotoxicity in the subsequent crop. Therefore, this management is recommended where plants occur at different stages of development in the crop, with younger plants tending to be more susceptible, and larger plants requiring greater attention to have efficient control.
Species that are difficult to control, or that are resistant to certain herbicides such as horseweed (Conyza spp.) and pigweed (Amaranthus spp.), can also be better controlled with sequential applications.
It is also common for there to be many emergency flows of weeds in the productive environment, due to a large seed bank that may exist in some areas. In these cases, sequential applications are also a good alternative to ensure that the crop remains clean until the crop of interest emerges. Rain immediately after application is also a factor that can reduce the efficiency of the application, therefore, a sequential application would be a suitable alternative for controlling weeds.
In general, this technique allows weeds that remain in the field or have resprouted due to resistance, difficult control, emergency flow or failures in the first application, to be controlled in sequential applications.
How to perform sequential application
The initial step is to identify the target weed species and choose the mechanisms of action, which depend on the control spectrum of the characteristics of each herbicide. To avoid the selection of resistance, it is important to combine different mechanisms of action, indicating the non-repetition of active ingredients in applications and the use of contact and systemic products, which in addition to preventing the appearance of resistant biotypes, also increases the spectrum and action efficiency. It is essential to follow each manufacturer's recommendations to avoid antagonism and phytotoxicity.
The first application should be made at a time when the majority of weeds are present, preferably before they reach an advanced growth stage. Subsequently, it is necessary to monitor the crop, observing control symptoms, such as signs of necrosis, death and the number of plants that germinated or survived. The second application generally occurs 7 to 14 days after the first, depending on the speed of emergence of new weeds and weather conditions, targeting mainly plants that emerged or were not controlled in the first application.
Saflufenacil for weed control
Saflufenacil is a broadleaf plant herbicide with contact action, belonging to the chemical group pyrimidinedione, which acts as an inhibitor of protoporphyrinogen oxidase (PROTOX). The herbicide has demonstrated high efficiency in several crops, such as soybeans, corn and cotton, controlling species such as sunn hemp and horseweed. It can be applied pre- and post-emergence, with the second option being more suitable. In desiccation for direct planting, it can be used in the first application for quick control. In areas with high infestation, you can opt for a sequential application, with an interval of 7 to 10 days, combining it with another systemic herbicide such as glyphosate to increase effectiveness.
Text written by Caetano Rocha and Dyeferson dos Reis Rocha, academics from the Agronomy course at UFSM, Frederico Westphalen campus, members of the Tutorial Education Program - PET Agricultural Sciences, under the supervision of the tutor, professor Dr. Claudir José Basso.
