Forestry carried out worldwide and especially in Brazil has undergone major developments in recent years. Brazil has favorable characteristics for this activity and the productivity levels obtained recently demonstrate Brazil's advantages for the production of planted forests. Weeds coexist with human activities and have a major impact on forestry activities.

Weed control has undergone major revolutions in recent years in grain production situations. In forestry, these changes are more recent, but they arrived with great intensity and point to major developments in the near future. Forestry has particular characteristics in relation to other activities in relation to weed control. On the one hand, there is the effect of long-term perennial cultivation and, until recently, the great tolerance by the technicians involved to the presence and control results of weeds with only a satisfactory effect.

On the other hand, the operationalization of field production is impacted by the industry's production engineering system. This has positive effects in relation to controlling the quality of the activities carried out, but has difficulties in dealing with biological phenomena associated with soil-herbicide-plant, weed-forest and planted-atmosphere interactions.

The evolution of forestry must consider this interaction and advance in the particularization of management no longer according to predetermined recipes, but based on specific surveys and localized application of herbicides or other control methods. Several factors are involved with this need.

Herbicide availability:
The herbicides recommended for use in forestry in Brazil were limited in number until recently and this hindered the best use of this weed control tool. However, a greater number of active ingredients have recently been registered, mainly for eucalyptus crops and to a lesser extent for pine. There is still a great lack of registered products for other forest plantation species such as acacia, poplar, teak and other species.

There is a need that the forestry sector, through the industries involved or their cooperative organizations, work together with the government bodies involved with the registration of phytosanitary products and with the producing or distributing industries of these products so that new herbicides are made available. In many of these companies and government bodies there is still no perception of the need to make more modern active ingredients available for improvement of weed control and greater environmental sustainability of forestry activities in Brazil.

New application technologies:
Recent advances in application through drones and digital agriculture are already impacting and are expected to further impact weed control activities in forestry plantations. Much of the beginning of the use of drones to apply herbicides in Brazil began in forest plantations, mainly as a way of replacing the application through knapsack sprayers, which represent a large operational cost and demand for labor.

Drone application has become increasingly common in Brazil for the application of phytosanitary products to various crops. Unfortunately, it is observed that in many situations there are application quality problems due to the prioritization of operational performance to the detriment of meeting the environmental conditions and particular technical characteristics of each equipment in use. This problem does not only affect forestry applications, but also occurs in other crops.

Digital agriculture:
One of the great advances in digital agriculture is the identification of spatial variability and the presence of weeds through sensors embedded in land vehicles, drones, aircraft or satellites. This technology has particular application in forestry and certainly represents a major evolution to be developed in this sector. The production cycle of approximately five to seven years and the low occurrence of machine traffic in forest plantations results in the occurrence of weeds with great unevenness compared to crop crops or perennial plantations of fruits or other species.

The existing non-uniformity in forest plantations is associated with the variability of species, infestation density, mixed species composition and the long production cycle. Currently, this variability is not considered in a large part of forestry plantations due to operational difficulties, and copying of weed control systems and crop cultivation where product choice and dose definitions are made based on a few weed species and at a similar stage of development.

However, in forestry plantations the rule is non-uniformity of species, multiple composition, density and stage of weeds, soil and environment. However, until recently, even if it were possible, it did not make sense to consider this variability as there were few herbicides available and ways of applying these products. However, technologies for prior mapping of plant infestation, soil characteristics, identification of weeds in real time or in advance, localized application with terrestrial equipment or drones are in rapid development.

The use of these tools will allow the definition of herbicides and mixtures, dose variation and real need for application. This will represent a major evolution in the rational control of weed competition in forestry. Previous mapping and identification in real time will provide the implementation of the pillars of integrated weed management related to periods of competition and level of economic damage that have limited applicability in current management carried out in a total area and on a schedule.

Improve the management currently carried out:
The implementation of current weed control measures requires improvements in several areas of forestry plantations. For example, pre-planting desiccation should be considered as a key activity. Currently, this operation is generally carried out through just one application and is often implemented right before planting. In many areas there is a long period between harvesting and planting, which favors the establishment of weeds. In the case of perennial weeds, soil preparation will result in the fragmentation of structures with reproductive capacity that will resume growth after new planting.

This situation, combined with the occurrence of multiple emergency flows and the occurrence of weeds that are difficult to control with the herbicide glyphosate, result in a peculiar characteristic in many forest plantations related to imitations of control efficiency in the desiccation operation. This operation must be improved by carrying out sequential operations, with mixtures of systemic products in the first and contact products in the second application, and products adapted to the spectrum of weeds existing in each area.

Biotechnology, herbicide resistance and physical methods:
New technologies for the use of herbicides and new problems related to the use of herbicides have also arrived in forestry. The recent availability of transgenic plants resistant to the herbicide glyphosate in eucalyptus crops demonstrates the technology of this activity in Brazil. However, the great flexibility and efficiency of this herbicide should not result in its single and continuous use due to the high risk of selecting weeds resistant to the herbicide glyphosate.

The problems of weed plants resistant to this and several other herbicides already exist in forest plantations in Brazil. This must be considered when planning the use of herbicides and requires diagnosing the occurrence of resistant weeds. This procedure is not yet carried out in almost all forest plantations and represents a necessary evolution in this sector. Adequate management of resistance and the use of herbicides characterizes the integrated management of weeds, which is based on the rationalization of herbicide use and the use of alternative control methods.

Currently, there is a resumption of development of physical methods of controlling weeds, such as electricity, laser beams and flaming. These methods are still expensive and have efficiency limitations, but they represent possible developments in weed control that could be used in forestry.

Need to evolve the perception of weed competition:
Recent changes in the control of weed competition in forestry in Brazil indicate that the system has been unlocked in relation to the development and use of modern weed control technologies. Several countries with high forestry production have a greater supply of labor and because of this they still use old vegetation management procedures. In countries with developed forestry such as Brazil, the low availability of labor and the need to adapt to strict environmental requirements are resulting in the development of highly complex technologies.

The high levels of technology in forestry must be accompanied by changes in the perception of weed competition problems in relation to the damage caused by weeds, the way in which herbicides are used and other control tools. However, the main need is to improve the perception of the variability of soil-herbicide-plant, weed-forest and planted-atmosphere interactions in relation to decision making based on the characteristics of each area to the detriment of simplifications of fixed and pre-established measures.



Area with limitations in weed control due to low efficiency in desiccation operations and pre-emergence herbicide application (left), and area free from weed competition resulting from adequate control during desiccation and during the initial growth of eucalyptus plants provided for the correct choice of herbicide applied pre-emergence (right).