Cultivar Selection and Placement of Shadecloth on Midwest High Tunnels Affects Colored Bell Pepper Yield, Fruit Quality, and Plant Growth

Abstract

Growing colored bell peppers in high tunnels enhances fruit quality and accelerates ripening. While there are benefits to high tunnel pepper production, increased heat inside the structures can lead to plant stress, blossom drop, sunscald, and reduced marketable yields. The objective of this study was to test shadecloth treatments placed on high tunnels to mitigate heat stress and improve colored bell pepper yield and fruit quality, while also identifying cultivars that perform well within Midwest high tunnel systems. Research was conducted at the Iowa State University Horticulture Research Station (Ames, IA) from 11 May to 11 Oct. in 2017 and 3 May to 9 Oct. in 2018. Six single-poly passively ventilated Quonset high tunnels were used for the experiment. The shade treatments (no shadecloth, 30% light-reducing shadecloth, and 50% light-reducing shadecloth) were applied in June of each season. Within each shade treatment, there were three randomized complete blocks of the seven colored bell pepper cultivars (Archimedes, Delirio, Flavorburst, Red Knight, Sirius, Summer Sweet, and Tequila). Data were collected on yield, fruit quality, and plant growth characteristics. Environmental parameters were monitored throughout the growing season. Both the 30% and 50% shadecloth treatments reduced monthly average and maximum air temperatures within high tunnels, with the largest differences occurring in the months of July and August. The use of a shadecloth reduced the incidence of sunscald by 59% between no shade and 50% shadecloth treatments. While there was no difference between 30% and 50% shade treatments, the use of 50% shadecloth caused a decrease in both marketable number (32%) and weight (29%) of pepper fruit compared with the control. ‘Tequila’, ‘Delirio’, and ‘Flavorburst’ had more marketable fruit per plant. Shade treatments did not affect fruit soluble solids content (SSC), pH, or total titratable acidity (TTA). Shade treatments had no effect on Soil Plant Analysis Development (SPAD) readings, shoot biomass, the number of leaves per plant or the total leaf area per plant; however, plant height increased by an average 14.5 cm for plants under shadecloth treatments. Average leaf size was 11.2 cm2 larger on plants grown under the 50% shadecloth, compared with the control. Several cultivar differences existed for each fruit quality and plant growth parameter. While differences in fruit quality and plant growth parameters were limited among shade treatments, decreasing marketable yield is concerning. Our research suggests that Midwest growers should not exceed 30% light-reducing shadecloth on their high tunnels for colored bell pepper production.