The effect of anti-hail nets on fruit protection, radiation, temperature, quality and probability of Mondial Gala apples

Abstract: The effects of crystal (transparent) and black nets on the protection of fruits from hail, the interception of light, temperature, humidity and fruit quality were evaluated over four seasons (from 2000 to 2003) at the IRTA-Experimental Station, Lleida (NE-Spain) on 'Mondial Gala' apples (Malus x domestica Borkh.). Nets demonstrated their efficiency for fruit protection against hail; decreased maximum orchard temperatures and increased minimum temperatures and relative humidity. Based on PAR values, on sunny days, the black net intercepted 25% more incident radiation than the control and the crystal net intercepted 12% more. The use of black net resulted in a significant reduction of colour intensity and days taken for maturity, and provided lower average yields for fruit harvested at the first picking. The crystal net was associated with intermediate values between black net and control, or similar values to those of the control. Both nets reduced fruit temperature and the incidence of sunburn improving global skin quality. The black net increased the vigour of the trees. Fruit firmness was not affected by the use of nets. Soluble solid content decreased when black net was used, while maturity was delayed in some seasons. There were no consistent effect with respect to titratable acidity and fruit cracking. The annual cost of the anti-hail nets was 1874 to 1612 ? ha¹, respectively, for crystal and black nets, depending mainly on the durability of the net. The annual cost of insurance was 760 ? ha¹ and was determinated by site, cultivar, yield and price insured, and was lower than that of covering by nets. The gross profit corresponding to the crystal net (8896 ? ha¹) was lower to the control/insurance (9223 ? ha¹) and greater to the black net (7842 ? ha¹) because of the reduction in fruit colour. With 'Mondial Gala' apples, the use of both colour nets was not economically beneficial compared to the control.