Strawberries are among the most popular fruit in the United States based on total crop value and fresh sales at grocery stores [Produce Marketing Association, 2018; U.S. Department of Agriculture (USDA), 2017]. Most strawberry acreage in the United States is conventional, but demand for organic strawberries is on the rise (Daugaard, 1999; Gu et al., 2017; Hoover et al., 2014). The high value placed on local agriculture, organic production, and direct market sales (Tourte et al., 2016) has led to increasing demand around the country for locally produced fruits and vegetables (Howard and Allen, 2010; Jensen and Malter, 1995; Tourte et al., 2016). Currently, the U.S. strawberry industry is concentrated in California and Florida (USDA, 2017). Growers who are able to supply local and organic strawberries in other parts of the country have a competitive edge in the direct-to-consumer market (Kadir et al., 2006a; Petran et al., 2017).
Climate plays a major role in determining regional and site suitability for strawberry production (Rysin et al., 2015). Depending on the cultivar, strawberry can be sensitive to variables such as late spring frosts, low winter minimum temperatures, and short growing seasons. There are two types of commercially produced strawberry cultivars: June-bearing and day-neutral (Darrow and Waldo, 1933; Gu et al., 2017). Nationally, most commercial strawberry producers use day-neutral cultivars for their longer season and higher yield potential compared with June-bearing cultivars, but historically, day-neutral cultivars have not performed well in northern regions of the United States (Darrow and Waldo, 1933; Petran et al., 2017). However, recent developments in breeding and protected environment agriculture have created new opportunities for producing day-neutral strawberries as annuals in some regions of the United States where conditions have traditionally been considered unsuitable (Hoover et al., 2014; Petran et al., 2017; Solomon et al., 2001).
Growing strawberries under protection can have many benefits. Shielded from rain and hail, fruit sustain less damage under high tunnels than in open fields (Jett, 2007). Berries are also cleaner with less surface moisture at harvest (Karlsson and Werner, 2011), and tunnels can increase the length of time during which strawberries can be harvested (Kadir et al., 2006a; Rowley et al., 2011). High tunnel strawberry production has also been shown to promote earlier flowering and fruiting when compared with open-field production (Kadir et al., 2006a). The more diffuse light conditions under tunnels may result in better light penetration to lower leaves, thereby increasing photosynthesis (Baeza and López, 2012; Demchak, 2009). One of the most important benefits of tunnels is disease management due to the lack of moisture accumulation on leaves in a sheltered environment (Burlakoti et al., 2014; Daugaard, 1999; Demchak, 2009).
Low tunnels are similar to high tunnels but relatively unexplored as a strawberry protected environment tool. In the low tunnel system, strawberries are grown on raised beds with plastic mulch. Steel hoops spaced evenly down the length of a bed support a plastic covering roughly 2 ft above the raised bed (Demchak and Hanson, 2013; Gu et al., 2017; Hoashi-Erhardt et al., 2013; Kadir et al., 2006a; Lewers et al., 2017). Low tunnels offer some unique advantages over high tunnels. Long-term high tunnel growers have identified soil compaction and quality as an issue in their systems (Demchak and Hanson, 2013). Low tunnels, which are not permanent structures, can easily be moved to new fields annually, reducing the risk of soil compaction. This also gives growers more flexibility in adjusting the scale of production from year to year. Soil-borne diseases are problematic in strawberry production, and having the ability to rotate the planting area can improve the sustainability of strawberry production systems. This is especially true in organic systems where synthetic soil fumigants cannot be used for disease management (Rysin et al., 2015). Other problems growers have observed with high tunnels include building and maintenance costs (Lewers et al., 2017), difficulties with temperature management, and loss of tunnels in extreme weather (e.g., severe winds and excessive snow) (Demchak and Hanson, 2013). Low tunnel materials may be expensive initially, but the hoops can be reused year after year, and actual tunnel construction is relatively simple. Temperature management is fairly easy as low tunnels do not require complex venting schemes—the sides can be opened and closed manually, and some tunnel plastics incorporate ventilation holes that run the length of the plastic. Air circulation, coupled with protection from rain, ensures that foliage, flowers, and fruit remain dry for longer periods of time, which can reduce the duration and frequency of disease infection periods (Karlsson and Werner, 2011).
For growers interested in low tunnels, new plastics designed for specific light absorption and transmission characteristics are now commercially available (Karlsson and Werner, 2011). In northern climates with short growing seasons, nontraditional plastic materials that operate as photo-selective barriers could improve crop performance or even aid in pest and disease control in a tunnel system (Baeza and López, 2012; Karlsson and Werner, 2011; Krizek et al., 2005; Paul et al., 2005). These plastic films selectively block or absorb wavelengths of light in the IR or ultraviolet ranges, or diffuse incoming direct beam solar radiation without inhibiting necessary transmission of photosynthetically active radiation (PAR). PAR includes both visible light and the spectral range important for photosynthesis, 400–700 nm (Björn, 2015). The standard films most commonly used in horticultural production transmit lower levels of ultraviolet light, allowing little or no transmission of ultraviolet-B (280–315 nm) and reduced transmission of ultraviolet-A (315–400 nm), but there are now other films that are completely opaque to ultraviolet light (Krizek et al., 2005; Paul et al., 2005).
Changing levels of light exposure can influence many aspects of crop morphology and chemistry (Ballaré et al., 2011, 2012). Total soluble solid content may be affected by the amount and quality of light a plant receives (Perkins-Veazie, 1995). Some studies have shown that fruit color and plant growth may be negatively affected by restricted ultraviolet exposure (Elfadly et al., 2012; Tsormpatsidis et al., 2011). And there is evidence suggesting that exposure to ultraviolet light improves crop resilience in the face of environmental stressors by way of photoreceptors that trigger critical defense mechanisms (Ballaré et al., 2012; Wargent et al., 2011). At the same time, restricting ultraviolet light can reduce the spread of diseases that affect strawberry fruit quality (Baeza and López, 2012; Karlsson and Werner, 2011; Krizek et al., 2005). Although it is generally understood that ultraviolet exposure can be harmful in some ways and helpful in other ways for plants, it is unknown how changing levels of ultraviolet exposure could affect overall growth and performance of strawberry plants under low tunnels.
The objectives of this study were to evaluate the effects of ultraviolet-blocking and ultraviolet-transmitting plastics on the light and microclimate in low tunnel environments and on fruit yield and quality. We evaluated these questions in the context of an organic field production scenario as we were primarily interested in practical applications for a strawberry grower producing for local organic markets. The broader context of this study is about improving the availability and quality of strawberries and sustainable production in a cold climate to help growers meet the demand for more local strawberries.
BallaréC.L.CaldwellM.M.FlintS.D.RobinsonS.A.BornmanJ.F.2011Effects of solar ultraviolet radiation on terrestrial ecosystems. Patterns, mechanisms, and interactions with climate changePhotochem. Photobiol. Sci.10226241
BjörnL.O. (ed.).2015Photobiology: The science of light and life. 3rd ed. Springer New York NY
BurlakotiR.R.ZandstraJ.JacksonK.2014Evaluation of epidemics and weather-based fungicide application programmes in controlling anthracnose fruit rot of day-neutral strawberry in outdoor field and protected cultivation systemsCan. J. Plant Pathol.366472
CondoriB.FleisherD.H.LewersK.2017Relationship of strawberry yield with microclimate factors in open and covered raised-bed productionTrans. Amer. Soc. Agr. Biol. Eng.6015111525
de Lima NechetK.HeckD.W.TeraoD.de Almeida Halfeld-VieiraB.2015Effect of the increase of UV-B radiation on strawberry fruit qualityScientia Hort.193712
ElfadlyE.M.WargentJ.J.SobeihW.MooreJ.P.PaulN.D.2012UV radiation as an exploitable and diverse tool in the regulation of crop quality and yieldActa Hort.9566774
Gigahertz-Optik Inc2008Plant physiology. 15 Nov. 2017. <https://light-measurement.com/plant-physiology/>
Hoashi-ErhardtW.MooreP.CollinsD.BaryA.CoggerC.2013Evaluation of day-neutral cultivars for organic strawberry production in WashingtonActa Hort.1001167174
HooverE.Wold-BurknessS.PoppeS.PetranA.JordanE.HuguninP.2014Cold climate strawberry farming. 31 May 2019. <http://hdl.handle.net/11299/164095>
HooverE.RosenC.LubyJ.Wold-BurknessS.2016Day-neutral strawberry production in Minnesota. 31 May 2019. <http://hdl.handle.net/11299/197960>
JensenM.H.MalterA.J.1995Protected agriculture: A global review. World Bank Tech. Paper No. 253
JettL.W.2007Growing strawberries in high tunnels in Missouri. 18 Dec. 2017. <https://www.hort.vt.edu/ghvegetables/documents/High%20Tunnel%20Construction%20and%20Crop%20Production/High%20Tunnel%20Strawberries%20by%20Lewis%20Jett.pdf>
KadirS.SidhuG.Al-KhatibK.2006bStrawberry (Fragaria ×ananassa Duch.) growth and productivity as affected by temperatureHortScience4114231430
KrizekD.T.ClarkH.D.MireckiR.M.2005Spectral properties of selected UV-blocking and UV-transmitting covering materials with application for production of high-value crops in high tunnelsPhotochem. Photobiol.8110471051
LewersK.S.FleisherD.H.DaughtryC.S.T.2017Low tunnels as a strawberry breeding tool and season-extending production systemIntl. J. Fruit Sci.17233258
MiyazawaY.HikosakaS.GotoE.AokiT.2009Effects of light conditions and air temperature on the growth of everbearing strawberry during the vegetative stageActa Hort.842817820
MoserR.RaffaelliR.Thilmany-McFaddenD.2011Consumer preferences for fruit and vegetables with credence-based attributes: A reviewIntl. Food Agribus. Mgt. Rev.14121142
National Weather Service2017Weather information for the Twin Cities. 1 Jan. 2018. <https://www.weather.gov/mpx/mspclimate>
PalmieriL.MasueroD.MartinattiP.BarattoG.MartensS.VrhovsekU.2017Genotype-by-environment effect on bioactive compounds in strawberry (Fragaria ×ananassa Duch.)J. Sci. Food Agr.9741804189
PaulN.D.JacobsonR.J.TaylorA.WargentJ.J.MooreJ.P.2005The use of wavelength-selective plastic cladding materials in horticulture: Understanding of crop and fungal responses through the assessment of biological spectral weighting functionsPhotochem. Photobiol.8110521060
PetranA.HooverE.HayesL.PoppeS.2017Yield and quality characteristics of day-neutral strawberry in the United States upper Midwest using organic practicesBiol. Agr. Hort.337388
Produce Marketing Association2018Top 20 fruits and vegetables sold in the U.S. 19 Dec. 2018. <https://www.pma.com/content/articles/2017/05/top-20-fruits-and-vegetables-sold-in-the-us>
R Core Team2013R: A language and environment for statistical computing. R Foundation for Statistical Computing Vienna Austria
RowleyD.BlackB.L.DrostD.2011Late-season strawberry production using day-neutral cultivars in high-elevation high tunnelsHortScience4614801485
RysinO.McWhirtA.FernandezG.LouwsF.J.Schroeder-MorenoM.2015Economic viability and environmental impact assessment of three different strawberry production systems in the southeastern United StatesHortTechnology25585594
SamtaniJ.B.AjwaH.A.WeberJ.B.BrowneG.T.KloseS.HunzieJ.FennimoreS.A.2011Evaluation of non-fumigant alternatives to methyl bromide for weed control and crop yield in California strawberries (Fragaria ananassa L.)Crop Prot.304551
SolomonM.G.JayC.N.InnocenziP.J.FitzgeraldJ.D.CrookD.CrookA.M.EasterbrookM.A.CrossJ.V.2001Review: Natural enemies and biocontrol of pests of strawberry in northern and central EuropeBiocontrol Sci. Technol.11165216
TsormpatsidisE.OrdidgeM.HenbestR.G.C.WagstaffeA.BatteyN.H.HadleyP.2011Harvesting fruit of equivalent chronological age and fruit position shows individual effects of UV radiation on aspects of the strawberry ripening processEnviron. Exp. Bot.74178185
U.S. Department of Agriculturen.dStrawberries grades and standards. 2 July 2016. <https://www.ams.usda.gov/grades-standards/strawberries-grades-and-standards>
U.S. Department of Agriculture2017Noncitrus fruits and nuts: 2016 Summary. 9 Jan. 2018. <https://www.nass.usda.gov/Publications/Todays_Reports/reports/ncit0617.pdf>
WargentJ.J.ElfadlyE.M.MooreJ.P.PaulN.D.2011Increased exposure to UV-B radiation during early development leads to enhanced photoprotection and improved long-term performance in Lactuca sativaPlant Cell Environ.3414011413
WestJ.S.PearsonS.HadleyP.WheldonA.E.DavisF.J.GilbertA.HenbestR.G.C.2000Spectral filters for the control of Botrytis cinereaAnn. Appl. Biol.136115120