Off-target herbicide injury from dicamba and 2,4-D is an increasingly common problem for specialty crop growers in the Midwest U.S. Lettuce (Lactuca sativa L.) is a common specialty crops grown in Nebraska, but proximity to corn and soybean production leaves growers vulnerable to crop injury and significant economic loss. The goal of this study was to quantify crop injury and yield loss in greenhouse grown lettuce after exposure to simulated sub-lethal drift rates of 2,4-D and dicamba. Sublethal doses were determined based on a percentage of the maximum labeled rate and ranged from 25% to 0.01%. Tested lettuce cultivars included ‘Green Forest,’ ‘Vulcan,’ and ‘Allstar,’ and each was sprayed at seedling and mature growth stages. Plant injury ratings were recorded every 4 days after herbicide application until harvest, when final fresh weight yield was determined. Dose response curves were generated to determine effective dose (ED) values and to relate drift rates with crop injury and yield loss. All lettuce cultivars were more tolerant of herbicides at the maturity growth stage than at the seedling growth stage. Among cultivars, ‘Green Forest’ was most susceptible to injury from dicamba and 2,4-D. At the seedling stage, 1.4% dicamba caused 50% visual injury and 35% yield loss in ‘Green Forest,’ and 1% 2,4-D caused 10% visual injury and 20% yield loss. When ‘Vulcan’ was sprayed at the seedling stage, 10% 2,4-D led to plant mortality within 16 days of treatment, and 25% dicamba led to plant mortality within 22 days of treatment. Results confirm the susceptibility of lettuce to relatively low rates of 2,4-D and dicamba, which highlights the importance of drift mitigation efforts in the Midwest U.S
