Date of this Version
Off-target herbicide injury from dicamba and 2,4-D is an increasingly common problem for specialty crop growers in the Midwestern United States. Both lettuce (Lactuca sativa L.) and pumpkin (Cucurbita spp.) are common specialty crops grown in Nebraska, and their proximity to corn and soybean production makes these crops susceptible to herbicide drift injury and yield loss. The objectives of this thesis research was to quantify crop injury and yield loss in greenhouse- and field-grown lettuce and field-grown pumpkins at different growth stages after exposure to sub-lethal doses of dicamba or 2,4-D. Dose response curves were generated to determine effective dose (ED) values and to relate drift rates with crop injury and yield loss. In addition, a dicamba residue test was conducted in lettuce to relate residue levels, drift rates, crop injury, and yield loss. Our study found out all modern lettuce varieties ‘Green Forest’, ‘Vulcan’, and ‘Allstar’ were highly susceptible to dicamba and 2,4-D. Mature stage lettuce had higher tolerance for both herbicide but with observed high variation on yield. Some increase in yield was observed in mature stage lettuce but the benefits of the small increase in biomass was offset by visual injury and reduced marketability. 2,4-D choline caused yield reduction on seedling stage ‘Green Forest’ and ‘Vulcan’ at the rate above 21.3 g ae ha-1 with 50% yield loss at the rate of 33.6 g ae ha-1. ‘Green Forest’ at seedling stage were highly susceptible to dicamba with 50% yield loss when treated at the rate of 16.8 g ae ha-1. Pumpkins studies showed less susceptibility to dicamba and 2,4-D at flowering stage with high variability on yield that caused poor lack of fit on the dose-response model. Dicamba at the rate of 139.8 g ae ha-1 and 2,4-D at the rate of 266.6 g ae ha-1 caused significant yield reduction on vegetative pumpkins compared with the control. The results provided information to Nebraska growers and aid to quantify economic loss from off-target herbicide drift events and highlight the need for communication between commercial herbicide applicators and specialty crop growers.