Effect of a High Tunnel, Organic Cropping System on Lettuce Diseases in Western Washington

Abstract

Incidence of gray mold and lettuce drop, and yield of six cultivars representing market classes Boston/Crisphead, Leaf, and Romaine, were evaluated in open ended high tunnel and open field organic production systems near Mount Vernon, WA from 2010 to 2012. Each year seedlings were transplanted in April and heads harvested in June/July. In 2010, Romaine types had significantly (P < 0.0001) greater incidence of gray mold (caused by Botrytis cinerea) than other types. In 2011, incidence of gray mold was significantly (P = 0.004) greater in high tunnel than open field plots, and greatest in high tunnels when fog persisted. All cultivars were equally susceptible to lettuce drop (caused by Sclerotinia sclerotiorum), although in 2012, incidence was significantly (P < 0.0001) greater in high tunnel than open field plots. ‘Green Star’ (Leaf type) had reduced incidence of gray mold and lettuce drop in 2010 and 2011. Incidence of tipburn was significantly (P = 0.032 and P = 0.001, respectively) greater in the high tunnels in 2011 and 2012 compared to the open field. Total yield (kg) was greater in the open field in 2012, but not in 2011 and 2010. Accepted for publication 8 July 2013. Published 22 September 2013.