High Tunnel Lettuce Variety Yield and Quality When Grown In Different US Climates

Field studies were conducted during 2010 in Washington (WA), Tennessee (TN) and Texas (TX) as part of a 3-year USDA Specialty Crops Research Initiative Grant (CSREES Award Notification No: 2009-51181-05897) evaluating high tunnel (HT) lettuce yield and quality when grown in three distinct climates (TN – hot, humid; TX – hot, dry;  WA – cool, humid).  Six-week old lettuce varieties Adriana, Green Star, Jericho, Ermosa, Coastal Star and New Fire Red were transplanted into subplots (3 ft. x 14 ft.), both inside HT and in open field (OF) plots.  High tunnel and OF lettuce was transplanted 22 April in WA, while in TN and TX, lettuce was transplanted in HT and OF plots 25 March and 14 April, and 5 April and 22 April, respectively.  All plots were covered with black plastic mulch and drip-irrigated as-needed.  Crop fertility and pest management were maintained according to regional practices.  The trial was conducted as a split block design replicated four times; subplots contained 20 – 28 plants/variety (depending on state) spaced at 1 ft. in two staggered rows per bed.  On average, lettuce varieties in WA matured 55 – 63 days after transplanting (DAT) with no significant difference between HT and OF plots.  In TN, average lettuce maturity occurred at 50 – 61 DAT, and lettuce grown under HT matured significantly (P > 0.0001) later compared to OF plots (due to bolting in OF plots).  In TX, average lettuce maturity occurred 37 – 48 DAT and HT lettuce matured significantly earlier (P > 0.0001) than OF plots.  Total and marketable yields in WA and TX, averaged across varieties were equal in both HT and OF plots.  In TN, higher incidence of insect, disease and physiological damage in HT plots reduced lettuce quality and marketable yield (P >0.0002) although total yields were significantly higher (P > 0.0062). Lettuce head height/width diameter ratio averaged across varieties was equal between HT and OF in all three states.  Average lettuce internal core lengths for marketable lettuce were significantly greater (P > 0.0289) in HT-grown varieties in WA, while the opposite occurred in TX.  No internal core lengths were measured in TN.  These results indicate that HT culture may influence lettuce growth positively, negatively, or have no effect; and that additional physical and environmental factors associated within each location’s climate may have a critical role in determining the successful improvement in HT lettuce quality and marketable yields.