High tunnels are unheated season extension structures that allow growers in temperate regions to fulfill consumer demand for fresh market produce at times which are traditionally off-season (Conner et al., 2009). High tunnel production is well suited to high-value crops, such as tomato, bell pepper (Capsicum annuum), garlic (Allium sativum), strawberry (Fragaria ×ananassa), blackberry and raspberry (Rubus species and varieties), and multiple species of cut flowers (Lamont et al., 2003; Orzolek et al., 2002). As year-round consumer demand for fresh, locally grown, and organic produce continues to increase, more farmers markets and other direct marketing avenues are on the rise (Zepeda and Deal, 2009), creating opportunities for growers to adopt and benefit from high tunnel production.
Few production-based studies have evaluated the effect of high tunnels within an organic farming framework. High tunnel production systems are well suited to organic farming as tunnels are energy efficient and can improve the quality and yield of vegetables over field-grown systems (Lamont et al., 2003; Wittwer and Castilla, 1995). Many small-scale organic growers market locally and high tunnels can provide season extension and allow growers to capitalize on higher quality heirloom varieties that are in demand and would otherwise not be available in a long-distance distribution system. Organic growers have fewer pest management options than conventional growers and high tunnels can aid in pest control. High tunnels were shown to increase yield of organically grown tomato plants that received compost applications by reducing disease incidence and development of early blight (Baysal et al., 2009). From a quality standpoint, phytonutrient studies have shown differences in nutrient uptake in vegetables grown in high tunnels vs. open field plots and receiving organic-based vs. conventional fertilizers (Gent, 2002; Zhao et al., 2007).
Tomato is a high-value crop well adapted to the high tunnel system, where economic return can be higher compared with field-grown crops (Orzolek et al., 2002). In addition to earlier harvests, protected agriculture systems, like high tunnels, can increase fruit quality by reducing wind damage and injury from insects, diseases, birds, and rodents. Protected systems also provide crops with an indeterminate growth habit with a longer harvest season as compared with field production (Wittwer and Castilla, 1995).
Organically grown heirloom tomatoes provide a potentially lucrative niche as a segment of the overall fresh-market tomato sector. Many open-pollinated, heirloom tomato varieties have an indeterminate growth habit, simultaneously producing new vegetative growth and fruit over time, in contrast to determinate varieties that produce the majority of fruit within a discrete time period. Heirloom tomato varieties are growing in popularity and consumers will pay premiums above the cost of conventional hybrid fruit (Jordan, 2007). However, heirloom varieties can be challenging to produce because they tend to be physically inconsistent in growth and form and prone to bruising, splitting, and cracking; thus, their distribution is often limited to local fresh markets (Vavrina et al., 1997). High tunnel production can reduce splitting and cracking in heirloom tomatoes, thus improving quality.
In regard to the causes of fruit splitting or cracking, one common contributor is rapid water uptake that results in increased turgor pressure within the fruit, initiating cracks or splits (Dorais et al., 2004). In a high tunnel system, cracking can be reduced by scheduled drip irrigation, rather than contending with natural rain events in the open field. Direct sunlight exposure can also cause cracking (Emmons and Scott, 1997). High tunnels reduce direct exposure from the sun and reduce foliage loss because of diseases. High tunnels create a microclimate that impacts abiotic and biotic factors and influences plant growth and development. Minimized fluctuations in day and night temperatures, increased soil temperature, elevated carbon dioxide (CO2) levels, and changes in soil moisture and spectral light quality are environmental conditions associated with tunnel production (Millner et al., 2009; Wittwer and Castilla, 1995). Increasing soil and air temperatures and CO2 levels hasten plant growth and maturation, especially in plants with an indeterminate growth habit, and influence yield quality (Morrison and Lawlor, 1999). Simultaneously, these changes impact plant disease incidence within the high tunnel system.
High tunnel coverings affect the quality of light reaching the foliage. Plastic coverings that absorb ultraviolet light at 340 nm can reduce the incidence and severity of some diseases, including gray mold (Botrytis sp.), white mold (Sclerotinia sclerotiorum), and leaf mold (Fulvia fulva) by inhibiting sporulation (Gullino et al., 1999). Furthermore, plastic coverings may increase the amount of ultraviolet B (medium wave) radiation reaching the plants, inducing chromosomal changes that affect production of secondary metabolites and plant chemistry that can translate to increased systemic resistance to plant pathogens (Raviv and Antignus, 2004).
High tunnels also reduce foliar pathogens by limiting spore dispersal via water. Early blight is a persistent, economically important foliar disease of tomato causing premature defoliation and reducing the photosynthetic ability of infected plants. Development of early blight is increased by leaf wetness, inoculum density, and age of the plant; host plant susceptibility also varies by variety (Vloutoglou and Kalogerakis, 2000). High tunnel systems provide shelter from rain and soil splashing, thus may decrease early blight severity by keeping the foliage clean and dry. Additionally, planting date can also influence disease development. Plant diseases caused by anthracnose (Colletotrichum sp.), early blight, southern blight (Sclerotium rolfsii), and septoria leaf spot (Septoria lycopersici) were more severe among early planted tomato than late planted field-grown tomato, regardless of fungicide treatment (Kennedy et al., 1983). High tunnels can mitigate these challenges by regulating temperature and moisture and may help reduce disease pressure.
The objective of this study was to determine the impacts of high tunnel production and planting date on heirloom and hybrid tomato varieties by observing differences in plant growth, yield, marketability, and early blight development within an organic production system.
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