EFFECT OF SHADE ON QUALITY OF GREENHOUSE TOMATO

Some amount of shade may be optimal to produce high quality tomatoes in a greenhouse during summer months in the northeast USA. Tomatoes were grown in a similar way in 2000, 2001 and 2002, except that the greenhouses were covered with reflective aluminized cloth that provided 30% shade in 2000 and 2001, while they were not shaded in 2002. When the greenhouses were shaded, the fraction of tomatoes that were marketable was 10% greater than when they were not shaded. To determine the effects of shade more precisely, simultaneous comparisons were made among greenhouses that were either not shaded, or covered with reflective aluminized shade cloth that attenuated 0, 15%, 30% or 50% of direct sunlight. The shade cloth was applied at the start of warm weather in early June; one month after fruit began to ripen. The houses were shaded for the rest of the summer, and fruit was picked until late August. Total yield decreased linearly with increasing shade, but there was no difference among shade treatments in yield of marketable fruit in any of three years. The fraction of marketable fruit was greatest for plants grown under 50% shade. This fraction was 9% greater than in a greenhouse with no shade in 2003, and 4% greater in 2004 and 2005. Shade decreased average fruit size only in 2003. Cracked skin was the defect most affected by shade. Up to 35% of the fruit produced in greenhouses with no shade had cracked skin, whereas in greenhouses covered with 50% shade, only 25 to 29% of the tomatoes had cracked skin. Over three years, there was no consistent trend with shade in the fraction of fruit with green shoulder, blossom end rot, or irregular shape.