Incidence of diseases and needs of control in overhead covered grapes

The plastic overhead cover (POC) of grapes is increasing in Brazilian vineyards aiming to reduce physical and biological damages. The objectives of this work had been to characterize the incidence and severity of diseases, and, consequently, the needs of control, as well as to evaluate the residues of fungicides in POC conditions. The experiment was installed in 2005/2006, in Flores da Cunha-RS, in a vineyard cv. Moscato Giallo, led in Y Shape, with impermeable plastic covering (160 mu m), in 12 rows with 35m, being left 5 rows without covering (control). In both areas, the microclimate was evaluated with relationship to the presence of free water (visual register), temperature (T), relative humidity (UR) of the air, photosynthetically active radiation (PAR) and wind speed (WS) close to the leaves and clusters. In the covered area were only applied fungicides when necessary. In the control plants sprays were accomplished by calendar. Incidence and severity of downy mildew (Plasmopara vilicola), powdery mildew (Uncinula necator), botrytis (Botrytis cinerea), rip rot (Glomerella cingulata) and sour rot (imperfect yeasts) were evaluated in each area during the flowering and ripening. The impermeable plastic covering increased the air temperature at the leaves level, and did not influenced the relative humidity of the air, but reduced the photosynthetically active radiation and the wind speed, and restricted the free water drastically on the leaves and clusters. The covered area needed only two sprays for the powdery mildew control, while in the discovered area 17 sprays were accomplished for control of fungal diseases. There were no incidence of diseases in the flowering evaluation in both treatments, however in the ripening period there was significant decrease of incidence of sour rot (-77.10%) and severity of rip rot (-89.47%), botrytis (-57.56%) and sour rot (-84.54%). The POC increased the temperature at the leaves and clusters levels, did not have influence upon the UR, reduced the PAR and wind speed and restricted the free water drastically on the leaves. The POC did not allow the downy mildew establishment and reduced the incidence and severity of clusters rottenness, reducing the needs and the costs with control disease, and promote the smaller impacts of contamination for the environment, producer and consumer than conventional system. As the residual accumulation of fungicides is higher in POC compared to the conventional system, the control disease should be differentiated.