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Aroldo Ferreira Lopes Machado

Professor of Weed Management at UFRRJ - Federal Rural University Rio Janeiro


Weed management in forest protection

Among the various factors that contribute to the reduction of productivity in planted forests, weeds deserve to be highlighted, as they are species that negatively interfere with the different phases of the forest. Plant species, considered harmful, not only cause, due to the effect of competition, a reduction in the growth and development of tree species of interest, but can also hinder silvicultural operations, interfere with forest harvesting and even contribute to the occurrence of forest fires, among other negative interferences.

In this sense, to promote the total protection of planted forests, Integrated Weed Management assumes a prominent role. Integrated Weed Management consists of applying techniques to control competing species in forest stands in a rational manner, ensuring sustainable production at acceptable costs and environmentally safe. In recent years, Integrated Weed Management practices have been undergoing transformations, due to recent challenges, such as product positioning, behavior of herbicides in the environment, herbicide application technology which, consequently, provide opportunities for improvement in control of these plants.

This evolution in the Integrated Weed Management process can be observed on a larger scale in agricultural areas; however, in silviculture, despite being slower, it is possible to see conceptual changes in the management of weed competition , and, as a result, many companies in the forestry sector have bet on the use of new technologies to increase efficiency and reduce costs in the process of weed management.

In this context of considerations, operations such as identification of weeds present in the plots, control recommendations, use of herbicides applied in pre-and post-emergence, mixtures of herbicides in tanks, technology for applying herbicides by means of terrestrial sprayers (mechanized or manual ) or the use of Remotely Piloted Aircraft, known as drones, control of shoots and high costs of management operations are the main challenges of Integrated Weed Management in forestry. Therefore, it is necessary to adopt disruptive technologies as a way to increase management efficiency and generate value for the activity.

In this scenario of disruptive technologies, within what is defined as Forestry 4.0, the adoption of technologies such as the Internet of Things, Big Data, Machine to Machine, Machine Learning, artificial intelligence, satellites and sensors, is increasingly studied and used in the search for improvement in the management of weed competition. With regard to digital forestry, each year, new companies and startups appear on the market, offering technologies that, applied to field conditions, ensure the reduction of activity costs and efficiency gains in protecting forests.

The use of technologies related to digital forestry favors mapping, which is a technique for identifying invasive plants present in the forest. Detection is carried out using sensors that allow for improvements in estimating the distribution of plants in the area, since the phytosociological survey, carried out by the conventional method, demands a lot of labor and has low operational efficiency. In this way, precision silviculture has become a strong ally of the Integrated Weed Management, favoring weed mapping activities, since imaging technologies, by satellites, planes or drones, have been used in the survey of these plants, in total area or reboleiras, reducing operating costs and increasing accuracy of information.

With regard to herbicide applications in forestry, the activities can be carried out using land, costal or mechanized equipment and/or aerial equipment (Remotely Piloted Aircraft). In terrestrial applications with costal equipment, it is essential to train the workforce, in order to avoid problems with drift, low application uniformity, crop intoxication and the applicator's own intoxication.

In mechanized terrestrial applications, the type of application most used in forestry, it is possible to use instruments that, in the same operation, identify the presence of weeds and carry out the application of the herbicide. The use of drones favors, for example, the application of herbicides in areas of difficult access, areas with a high level of residues or in more specific applications, such as in the control of sprouting, using information from digital mapping.

Another challenge in silviculture is the use of pre-emergent herbicides, important products in the implantation and in the first months of the forest. The use of these products, however, requires both the knowledge of the physicochemical characteristics of the herbicides and the chemical and physical characteristics of the soil for the best positioning of these molecules, since the type of soil, the clay content and organic matter, the soil pH , the water content in the soil and the amount of residue influence the action of pre-emergents.

Currently, researchers have been working with mathematical modeling to increase the efficiency in the use of pre -emergent herbicides, seeking to identify models for choosing adequate doses, depending on the seed bank, soil type, clay content and soil density. organic matter. Another important point that deserves attention is the use, in forestry, of mixtures of herbicides in tanks, a very common practice, especially due to the advantages of reducing costs.

In addition, this technique provides agility in operations, ease of crop management, increase in the control spectrum, increase in weed control time when pre- and post-emergence are mixed, delay in the evolution of resistance of these plants to herbicides and decrease in soil compaction. Although used for a long time in Brazil, the regulation of tank mixes was published in 2018, by Normative Instruction number 40.

When it comes to tank mixes, it is necessary, above all, to know the compatibility of the mixed products, since, in some mixtures, antagonistic interaction between molecules can occur, with consequent loss of effectiveness. In this case, it is recommended to search for information about the compatibility of the mixtures and to carry out the jar test before processing them. There may also be synergism between the herbicides in the mixture, a reaction that, from the point of view of weed control, is a positive fact; however, it can cause or increase the phytotoxic effects of the herbicides on the crop.

As evidenced, weeds have the potential to reduce forest productivity and, therefore, the Integrated Management of Weeds is a forestry activity with the aim of protecting forests. Therefore, it is essential to understand the dynamics of weeds and the best way to manage them, adding the use of technologies that enable management, provide efficiency in operations and reduce costs and cause less impact on the environment. Because it is a complex activity, a good weed management program in forestry is necessary, and this must be done in the long term.