Weed Management in Cereals in Semi-Arid Environments: A Review [chapter]

Ins Santn-Montany, Encarnacin Zambrana-Quesada, Jos Luis Tenorio-Pasam
2013 Herbicides - Current Research and Case Studies in Use  
Inés San"ín-Mon"anyá, Encarnación Zambrana-Q"esada and José L"is Tenorio-Pasamón Addi"ional informa"ion is available a" "he end of "he chap"er h""p://dx.doi.org/10.5772/55970 . Introduction . . The weed problem on cereal arable fields With growing concern about the environment, and the increased public interest in environmental conservation, traditional agriculture has led to profound changes in in recent years. Cereals are the most important crop in dry-land areas of southern Europe. In Spain,
more » ... n Europe. In Spain, nearly . million ha of winter cereals are sown each year [ ]. Research in agriculture has undergone a paradigm shift, favoring systems aimed at improving the performance of cropping systems without deleterious effects to the environment. To achieve this, weed managers continually develop comprehensive programs for crop protection, in which an essential component is the use of crops more competitive with weeds [ ], in order to maintain the stability of agricultural production. The selection of a crop is not an easy task and it involves the consideration of numerous environmental and socioeconomic factors. "dditionally, in any cropping system, we always can observe the presence of weeds that invade, persist and survive. They are unwanted and we refer to them as plants "out of place". There are numerous definitions of a weed a plant that is out of place and not intentionally sown a plant that grows where it is not wanted or welcomed a plant whose virtues have not yet been discovered a plant that is competitive, persistent, pernicious, and interferes negatively with human activity. Weeds possess one or more of the following characteristics that allow them to survive and increase in nature abundant seed production rapid population establishment seed dormancy long-term survival of buried seed adaptation for spread presence of vegetative reproductive structures and ability to occupy sites disturbed by humans. © 2013 San"ín-Mon"anyá e" al.; licensee InTech. This is an open access ar"icle dis"rib""ed "nder "he "erms of "he Crea"ive Commons A""rib""ion License (h""p://crea"ivecommons.org/licenses/by/3.0), which permi"s "nres"ric"ed "se, dis"rib""ion, and reprod"c"ion in any medi"m, provided "he original work is properly ci"ed. Therefore, to control effectively we should ask why do weeds emerge; and what factors limit their development?. There is abundant evidence that the presence of weeds reduce crop yields weeds compete for environmental resources, especially water, light and soil nutrients, resulting in decreased crop yield or reducing the crops quality by contaminating the commodity, interfering with harvest, serving as hosts for crop diseases or providing shelter for insects to overwinter, limiting the choice of crop rotation sequences and cultural practices. The most important parameters that characterize the infestation of weeds in a crop and that determine the competitive relationships between them are the density and time of weed competition. Their competitive ability is associated with the establishment of a dense infestation, and is caused by the different habits of growth of weeds and crops. Weeds have developed a number of features that allow them to survive and even dominate in adverse environmental conditions. "lso, to learn more about competition exerted by weeds is necessary to know their life cycle, and we can observe three major life cycle groups in cereal arable fields Annuals Summer annuals germinate in the spring, mature, produce seed, and die in one growing season. Winter annuals germinate in late summer or fall, mature, produce seed, and then die the following spring or summer. Biennials Weeds grow from seed anytime during the growing season. They normally produce a rosette of leaves close to the soil surface the first year, then flower, mature, and die during the second year. " true biennial never produces flowers or seeds the first year. There are relatively few biennial weeds. Perennials Simple perennials form a deep taproot and spread primarily by seed dispersal. Creeping perennials may be either herbaceous or woody and can spread by both vegetative structures as well as by seed. When we study the competition process between species, we must consider what resources are limiting in the environment, which will account for more competition. Since weeds are so prevalent in many areas of the landscape, management techniques are necessary to maintain order. Weed management is most successful when it involves an integrated approach using a variety of methods. The common methods used to manage weeds include prevention and cultural, mechanical, biological, and chemical means. Herbicides remain the predominant weed management tool with the greatest influence on weed selection over the last years [ ]. Reliance on chemicals for weed control has increased significantly in the last decades [ ]. However, herbicide use also carries risks that include environmental, ecological, and human health effects. It is important to understand both the benefits and disadvantages associated with chemical weed control before selecting the appropriate control. Many factors determine when, where, and how a particular herbicide can Herbicides -C"rren" Research and Case S""dies in Use 134 be used most effectively. Understanding some of these factors enables you to use herbicides to their maximum advantage. Urzúa [ ] recorded the following precepts . When any plant is established and persists in a given area, it is likely to have established a presence of seeds, tubers, rhizomes or other means propagative in the place that environmental conditions are favorable for reproductive success and competes successfully with established plant populations. Furthermore, morphological and physiological differences between plants being constantly selected will likely be the most suited to climate, soil and agricultural management, for their establishment and persistence and will likely dominate [ ]. Yenish [ ] pointed out that it is not economical nor practical to try to eradicate the most problematic species already established, when the presence of them is high in the soil seed bank in most cases, they can be kept under control with the application of herbicides. In a period of about five years we may reduce the seed bank to less than %, but we should also consider that in a single year without control, their seed production may be sufficient to exceed % of the original population [ ]. . The weed composition in different communities is not always the same, and it changes over time this has been called succession. "ccording to this theory, when the habitat remains relatively constant, we do not record considerable changes in the community. When the conditions are modified, the species adapted to the "original conditions" are replaced by those that the new environment is more conducive for their development. "t the same time, the presence of new species modifies the new environmental conditions and favors the establishment of other species [ ]. In agricultural land the succession process is different than in natural areas since agricultural practices constantly disrupt natural succession process, and the dynamic successional cycle begins. With the suspension of agricultural operations, successional processes in vegetative populations are restored [ ]. . The practices used by the farmers to produce their crops each year favor the development of certain species of weeds so that populations that occur in different plots reflect agricultural management provided to crops that year and previous years. . The competitive damage to the crop depends on the species, the density of each range, the proximity in which it is growing when they emerge to the crop plant and the duration of the competition. There are many species that do become problematic during a crop cycle in a particular field, depending on crop. However, it has been found that the early stages of crop development are more sensitive to competition by weeds. . Herbicides are available in the market, which when selected appropriately for each particular problem, can efficiently control weeds. To succeed, it is not enough to acquire and apply herbicides recommended for cultivation, it is necessary to take into account the factors that affect the efficiency of action of these herbicides, such as Weed Managemen" in Cereals in Semi-Arid Environmen"s: A Review h""p://dx.doi.org/10.5772/55970 135
doi:10.5772/55970 fatcat:q6uqtytic5cvxk47zqunkmphae