California and Florida are the two leading producers of strawberries in the United States (U.S. Department of Agriculture, 2012). The Florida farm gate crop value was about $290 million in 2015, from a crop grown on ≈10,700 acres (U.S. Department of Agriculture, 2017). The highest strawberry prices for growers in west-central Florida occur from late November to mid December (Tanino and Wang, 2008; Wu et al., 2012). Early strawberry planting (20–25 Sept.) is increasing in west-central Florida with the goal of increasing yield during this period. Although earlier fall planting dates tend to promote earlier onset of flowering and fruiting (Poling, 1993), the warm air temperatures experienced in west-central Florida during this time cause excessive running and plant growth, and reduce flower initiation and fruit yield (Heide et al., 2013). This situation presents a major challenge for strawberry production in this area.
Planting date recommendations for central Florida range between 25 Sept. and 25 Oct., depending on the cultivar (Whitaker et al., 2017). However, modern strawberry breeding programs focus on decreasing the requirement for low air temperature and multiple photoinductive cycles for flower bud induction. ‘Strawberry Festival’ and ‘Florida Radiance’ are the standard cultivars grown in Florida, mainly because of their large fruit size and flavor. Sweet Sensation® ‘Florida127’ is the newest released cultivar from the University of Florida Strawberry Breeding Program, showing improvement in fruit size and flavor compared with traditional cultivars (Kelly et al., 2016). As new heat-tolerant strawberry cultivars are released, greater early yield might be obtained as early planting dates are implemented (Rubinstein, 2015; Whitaker et al., 2014).
The most commonly used transplant type in Florida is bare root (Bish and Cantliffe, 2002; Bish et al., 1997). Bare-root leaf-on transplants promote earlier yield compared with those with leaves removed, but typically require high volumes of water via sprinkler irrigation after transplanting (Bish et al., 1997). Between 8 and 14 h·d–1 of continuous sprinkler irrigation are used to reduce the air temperature around the strawberry crown and keep leaves moist (Bish and Cantliffe, 2002; Bish et al., 1997). This irrigation practice accounts for one third of the total water required by the crop throughout the season (Hochmuth et al., 2006a), and it can impact the crop negatively by increasing disease dissemination and leaching nutrients out of the rooting zone (Bish et al., 1997; Hochmuth et al., 2006b). Lack of uniformity of bare-root transplants combined with plant damage created by sprinkler irrigation can contribute to reduction of early yield (Bish et al., 2001).
An alternative to sprinkler irrigation for plant establishment is the application of crop protectants after transplant (Santos et al., 2012b). Crop protectants provide a shield that reduces environmental stress on plants. During transplant establishment, naturally occurring materials such as kaolin clay, calcium carbonate, or aluminum silicate can be applied on top of the plant canopy. These materials act as reflective barriers to decrease ultraviolet and infrared radiation, therefore reducing heat stress on plants (Glenn and Puterka, 2005; Glenn et al., 2002, 2003). Crop protectants are widely used to reduce sunburn and decrease pest incidence on fruit such as apple (Malus domestica), pear (Pyrus sp.), tomato (Solanum lycopersicum), and pomegranate (Punica granatum) (Cantore et al., 2009; Glenn and Puterka, 2005; Glenn et al., 2002; Melgarejo et al., 2004). Previous studies reported that the application of kaolin clay reduced evapotranspiration rate and fruit temperature by 2 to 5 °C in apple and pomegranate (Glenn et al., 2002; Melgarejo et al., 2004; Wand et al., 2006). Santos et al. (2012b) reported 98% plant survival and no reduction in early yield in strawberry plants when kaolin clay was applied during establishment after 6 DSI for early October planting. Given the warmer maximum air temperatures of September compared with October (Fig. 1), it could be hypothesized that the effect of kaolin clay on plant establishment and early yield may be temperature dependent because the warmer air temperature associated with earlier planting (mid September) in strawberry production may influence the crop response to the application of the protectant.
To obtain the greatest possible early yield in Florida strawberry production, it is necessary to determine the most adequate combination of production techniques. The objectives of this study were to determine optimal planting dates for early strawberry production; determine the most adequate establishment practices for bare-root, leaf-on transplants for west-central Florida; and evaluate the effect of reduced irrigation water for establishment in strawberry production.
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