Enhancing the Productivity and Fruit Quality of Forced “Sweet Charlie” Strawberries Through Manipulation of Light Quality in High Tunnels

Abstract

In winter months, the U.S. domestic strawberry supply is low, demand is high, and unit price for strawberries is at its highest point during the year. Forcing strawberries in high tunnels during this time might capture this niche market. ‘Sweet Charlie’ plugs were conditioned from 24 Aug. to 12 Sept. at 24 oC on a 12-hour day/night cycle, and were planted on 12 Sept. in fertilized plots in a high tunnel (29.3 m long × 4.3 m wide × 3.1 m high). Conditioned plants were also planted outside on mulched, drip-irrigated beds as a control. Red, yellow, and pearl ChromatiNets (24% shade factor: lowest intensity possible) were installed over the top of the high tunnel in 7.3 m wide swathes, and a no-net control plot was included. Plants were fertigated weekly with about 3.2 kg N/hectare per week from 15 N–30 P2O4–15 K2O. High tunnels were vented to maintain day temperatures in the range of 25 to 30 oC. Runners were removed and counted beginning 24 Sept. until 17 Nov. when runnering stopped. Runner production was 59% greater with yellow and pearl nets compared with the no-net controls. In contrast, the red nets produced 38% fewer total runners and runners per plant than the yellow and pearl nets, but red nets produced 34% more runners than the no-net controls. Runner production of no-net plants in high tunnels was 20% greater in contrast to the plants growing outside. Yield data from fall/winter forcing and residual spring harvests did not show any great advantage to marketable weight and numbers with ChromatiNets. Marketable berry production began on 31 Oct., with berry production slowing in November and missing the Thanksgiving market window, with negligible production in December. The plants began to produce heavily in January, with greater yields with red nets and no-net controls along with significant reductions with yellow and pearl nets. In February, all three ChromatiNets yielded less than the no-net controls. In March, plants appeared exhausted; therefore, the high tunnel was opened and plants were allowed to acclimate to outside temperatures. By April, the outside plots were in full production, yielding more than any high tunnel treatments. In the high tunnel, however, yields resumed with the no-net control and yellow net yielding similarly, but red and pearl nets yielding less than the no-net controls. In May, all high tunnel treatments yielded less than the outside plots. The no-net control produced greater total yields of all net treatments and apparently, the ChromatiNets suppressed overall yield. It is probable that in winter, the ChromatiNet shading factor overwhelmed any light quality enhancement and in longer, warmer, and brighter days, the ChromatiNets may show an advantage.