Pre-emergent herbicides in the initial development of soybean and the impact on the production system

Abstract

Soybean is exposed to a series of factors that interfere its development, among them is the competition with weeds for the resources of the environment. Weed interference can cause problems as decrease in leaf area, dry mass, and grain weight, reducing the productive potential of soybean. Management with products that have a residual effect is quite promising, as it provides an initial suppression on the first layers of weed seeds, reduces the pressure of infestation, and improve the efficiency of post-emergent. However, the rates used, the physicochemical characteristics and the environmental conditions interfere in the absorption, translocation, or metabolism of these herbicides, being able to influence the behavior of these molecules and their efficiency and selectivity to crops. Thus, a study on the use of pre-emergent herbicides constitutes an important tool in programs for the management and prevention of weed resistance. The objective of the first article was to present a literature review, covering important information on weed management, with emphasis on pre-emergent chemical control and its impacts on the production system. According to the discussions presented, it is concluded that the use of residual herbicides in the control of weeds in the soybean crop has greatly helped, both in the management of the crop and, mainly, in the maintenance of an efficient production system. However, even with a relevant number of pre-emergent herbicides recommended for soybean, their use must be carried out considering numerous questions aimed at the sustainability of the production system. If wrongly positioned, they can generate symptoms of phytotoxicity in plants and carryover effect in the crop in succession, which happens when the pre-emergent herbicide shows residual activity greater than the interval between crops. These effects are directly related to numerous environmental and genetic factors, such as the characteristics of the herbicides, the physicochemical properties of the soil, humidity and temperature conditions, as well as the genetic variability of the cultivars used. In the second article, aiming to study the behavior of pre-emergent herbicides molecules in the initial development of soybean lines, five soybean genotypes were evaluated (R08-4004; R13- 40635RR; R14-1450; R16-1450 and KIRKSE45RR) treated with five pre-emergent herbicides (Classic©, Fierce©, Fierce XLT©, Valor EZ© and Zidua©), plus the control (without application), in two rates (recommended and rate), with three replications. After interpreting the data, it can be concluded that, for most of the evaluated characters, when the recommended rate of the pre-emergent herbicide was applied twice in the lines, they reacted negatively to the phenotypic performance, generating higher phytotoxicity estimates. The herbicide ValorEZ© showed a lower phytotoxicity effect, affecting less the development and initial growth of soybean seedlings, in addition to presenting an effective active principle in the control of weeds that affect the crop, according to the literature. The R08-4004 and UA KIRKSEY lines showed less damage to the characteristics evaluated in relation to the other varieties, results that allow us to infer that, probably, these genotypes have the greatest capacity to metabolize the entire active molecule absorbed by the plant.