Shade nets on table grapes

The use of covering nets is widely diffused in horticulture in order to protect plants from adverse conditions such as hail, wind or light excess, pest attacks, bird injury, hence, several type of articles are available. Most of nets are transparent (white), aiming at allowing light penetration, or also black or green when shading effect is desired. In the last decade, photo-selective colored nets have been also experimented in order to assess the effects that the change in light spectrum may exert on leaf functioning, shoot growth and fruit quality. Nevertheless, all nets reduce the amount of light available for the crop; in many cases the leaf net photosynthetic rate is reduced, but, on the other hand, leaves and fruits are protected from damages caused by excess of irradiance. Besides decreasing incident solar radiation, nets modifies the crop microclimate in terms diurnal pattern of air temperature and humidity; they may lower daytime temperature and vapor pressure deficit, but increase night temperature, enhancing atmospheric stability. Under semi-arid conditions, to limit the solar irradiance at canopy level may be useful to lower the transpiration rate and thus the crop water deficit. Hence shade nets may be helpful to attenuate the effects of multiple environmental stresses. On table grapes, the net use of nets is quite largely diffused, but, on the whole, relatively little information is still available on their physiological effects on leaf functioning and grape quality. The most used net types reduce wind speed by 80-85%, and photosynthetic photon flux by 10-25% or even more, according to the net color. In many cases vine vigor and yield are increased; sometime, negative effects on berry characteristics have been noticed, such as a poorer skin color. To avoid possible detrimental effects, canopy management and other cultural practices should be adapted to match better the needs of vines grown under shade nets.