Novel Low Tunnel Coverings and Plant Type Affect Productivity of Day-neutral Strawberries

Abstract

Growers producing day-neutral strawberries (Fragaria ×ananassa) in temperate climates face challenges when attempting to extend the season and mitigate the effects of rain. Conventional plastic coverings over low tunnels have been used for these purposes, but they often exacerbate heat-induced problems in summer. We examined two approaches for addressing this challenge. The first was to start dormant bare root ‘Albion’ strawberry plants in small pots in the greenhouse, then plant them into the field in spring so they could begin production before the onset of consistently high temperatures. Plants set in small pots on 26 Feb in the greenhouse and field planted on 6 May were compared with bare root plants set directly into the field on 6 May. The second approach used various low tunnel coverings to modify the light and temperature environment around the plants. Three coverings were woven nets embedded with reflective strips at various densities that allowed 50%, 60%, and 70% light transmission, and these were intended to lower temperatures under the covers by reflecting infrared radiation. A fourth covering was a polyethylene plastic embedded with optically active additives that shift incident light into wavelengths that are more photosynthetically active. Two other covers were standard commercial polyethylene plastics, and the final treatment was an uncovered control. Over the 2020 and 2021 growing seasons (hot and dry vs. moderate and wet, respectively), plots were harvested once or twice a week from June through October and fruit yield, size, and marketability were assessed. In both years, strawberry plants started in the greenhouse produced significantly higher yields than bare root plants over the season (30.5% and 43.7%). Bare root plants were less responsive to cover type than greenhouse plants. In 2020, yields tended to be higher in the middle of summer in plots with reflective coverings that reduced temperature and higher later in the season with coverings of wavelength-shifting film. Polyethylene covers that increased temperature without shifting the light spectrum had lower yields. Under the cooler conditions of 2021, plants under covers that increased temperature tended to have higher yields. In a third year (2023), bare root plants were covered with a reflective covering from 29 Jun until 1 Sep, then this cover was replaced with polyethylene with optical additives as the weather cooled and light levels dropped. This sequenced treatment was compared with uncovered plots and plots covered with standard commercial polyethylene plastic. Plants under the two-phase sequential covering performed significantly better than uncovered plots or those covered with standard polyethylene plastic alone.