Controllo malerbe nei cereali autunno-vernini

The control of weed represents one of the major issues in the cultivation of winter cereals. The presence of weeds in these, as in others crops, could in fact create significant quantitative damages, namely yield reduction as well as qualitative, due to the worsening of the characteristics of the grains (specific weight and protein content) and their contamination by weed seeds. The damaging effects determined by weeds are due to a series of negative interactions with the crops, mainly caused by the competition for the use of water, nutrients and light (in some cases also by allopathic effects and parasitism). The intensity of competitive phenomena depends not only on the characteristics of the weeds, but also on those of the crop and in particular its early growth and its adapting tools in the competitive environment. Concerning this aspects, grass weeds are the most dangerous infesting weeds for the winter cereals, being very similar to the crop species. Anyway, the higher height, the quantity of nutrients consumed during time unit and the water use efficiency are, the greater competitive capacity of the spontaneous plants is. The aggressiveness of weeds and their capacity to tolerate competition from the crops rely also upon some management and environment features of the crop itself. The planting time and weather conditions, such as rain quantity and temperature, become therefore particularly important for their strong influence on the crop and weed growth. Most common weeds of winter cereals are, among the grass weeds, Lolium multiflorum, Alopecurus myosuroides, Poa pratensis, Poa trivialis, Avena sterilis, Avena fatua and, among the broadleaf weeds, Stellaria media, Sinapis arvensis, Capsella bursa-pastoris, Papaver rhoeas, Fumaria officinalis, Matricaria chamomilla, Centaurea cyanus, Galium aparine, Veronica persica. Weeds can be controlled mainly with agronomic, mechanical and chemical means. One of the most effective agronomic means today is the crop rotation, frequently based on a two- or a three-year rotation. The use of this tool avoids the formation of weed infestations characterized by the presence of few species with high density, and also limits the development of phenomena such as soil fatigue development of insect pests and plant diseases. The mechanical means allow to control weeds by indirect (stopping their germination) and direct way (killing the already germinated plants). The indirect action consists of mechanical interventions for the preparation of the seedbed, which can determinate a different distribution of weed seeds, depending on the kind of mechanical tools that is used. In these conditions, the minimum tillage, concentrating the seeds on the upper part of the soil favor significantly the weed germination compared to the moldboard plowings. In the winter cereal it is possible to take action already grown weeds by using chain harrows very effective on the broadleaf weeds during their early stages. The use of these tools between the end of tilerining and the beginning of the stem elongation is not risky for the crops, even if sometimes their application is limited by the soil excessive humidity. The herbicides are today the most used tools for the weed management in winter cereals. The evolution over time has brought to the development of herbicides that are always less dangerous concerning the biological, toxic and environmental profile.