Numerous factors interfere with crop development, including competition with weeds for resources, which can be water, nutrients and light. When there is a decrease in one of these resources for the plant, there will be a reduction in productivity. We know that agriculture currently requires the adoption of new integrated practices in the management of weeds, with the use of herbicides with residual effects on the soil and covering the soil with straw being fundamental to reducing the harmful effects of invasive plants.
Thus, the arrival of herbicides in the soil is a determining factor in the efficiency of pre-emergence weed control. Due to the seed bank of weedy plants present in the soil, they are capable of emerging at different times in the crop cycle, which have staggered germination over time and, therefore, making their management difficult.
Therefore, herbicides applied before plant emergence have great advantages, as they can remain in the soil for a period of time, controlling weeds for a longer period. Thus, there will be no competition between them and the crop during the initial phases, reducing costs and reducing the seed bank present in the soil.
Mulching previous crops is an important physical barrier against the germination of weeds. However, many herbicides can be retained in the straw and be lost, either through volatilization or subsequent leaching. For control to be effective, the aerial application of these herbicides must reach the ground, that is, it must not be intercepted by mulch. Therefore, the amount of straw, the occurrence of rain after application and the physical-chemical characteristics of the herbicide must be considered, such as solubility, octanol-water distribution coefficient (Kow) and vapor pressure of the herbicide.
For transposition to occur in the straw, herbicides that act in pre-emergence must have high solubility in water, resulting in better translocation of the herbicide under the straw. Furthermore, the product must have low Kow to avoid retention, as the higher the Kow, the greater the sorption on the surface of the vegetation cover. Vapor pressure indicates the degree of volatilization of the product, therefore, the value must be low so that it is not lost to the atmosphere.
Furthermore, the occurrence of rain is a determining factor in the effectiveness of the product. Approximately 20mm of rain immediately after application results in shorter adsorption time in the straw, favoring the arrival of the herbicide into the soil. In the field, with the presence of different species of weeds, one must look for formulations that control more than one species, that is, look for herbicides in which the active ingredients have different modes of action and a broad spectrum of control.
The sulfentrazone + diuron mixture stands out for pre-emergence use in the control of eudicots and monocots in coffee, sugar cane, citrus, eucalyptus and soybean crops. Furthermore, it has systemic action and, due to its broad spectrum of action, it presents satisfactory control of weeds that are difficult to control and resistant to mechanisms of action such as glyphosate and ALS herbicides. The results obtained by GUBIANI et al. (2021) demonstrate this effect on the control of weeds in soybean crops, where with the application of the mixture at doses from 1.4Lp.c ha-1 (245+490gi.a ha-1) control of 90 % in clayey soils.
The herbicide sulfentrazone is an inhibitor of the enzyme protoporphyrinogen oxidase (PROTOX), and after application, it is absorbed by the leaves or roots and when the plants emerge and are exposed to light, they become chlorotic and die. Its action can be systemic or contact, with low movement through the phloem due to the rapid leaf desiccation caused by the product.
The herbicide diuron acts by inhibiting the electron transport chain in photosystem II, causing lipid peroxidation that leads to membrane rupture and, consequently, chlorosis and death. It is absorbed in smaller quantities by the leaves but quickly absorbed by the roots and transported through the xylem to the aerial part.
The analysis of factors that influence weed management highlights the importance of combining herbicides with residual effects and soil cover practices. The use of pre-emergent herbicides, such as a mixture of sulfentrazone and diuron, is effective in controlling several species, reducing competition for essential resources, and consequently increasing crop productivity. Furthermore, adequate straw management and consideration of variables such as solubility and climatic conditions are crucial to optimize the assertive application of herbicides. Thus, the integration of these strategies not only minimizes the presence of invasive plants, but also promotes a more sustainable and efficient agricultural system.
Text written by Gabriela de Azevedo Martins and Lidiane Bilibio Bonfada, members of AGR Jr. Consultoria Agronômica, Junior Company of the Agronomy Course at UFSM Campus Frederico Westphalen, under the guidance of professor Dr. Gizelli Moiano de Paula.
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