Differences in Tomato and Watermelon Cultivar Responses to Increasing Doses of Dicambart

Although dicamba can move long distances via off-target movement [5], significant damage to tomato, potato and watermelon has also been recorded at representative drift rates.[4] found that watermelon treated 20 days after planting (DAP) with 7.5 g ae ha -1 of the label rate of dicamba exhibited 40% visual injury and had vine lengths 49% the length of the non-treated AbstractDicamba can result in severe plant damage to sensitive crops, but differential tolerance to dicamba may be present among cultivars of these sensitive crops.Identifying tolerant cultivars of sensitive crops can limit the potential damage for growers if incidents of dicamba off-target movement occur.In central Missouri, a greenhouse study using seven tomato (Solanum lycopersicum) and five watermelon (Citrullus lanatus) cultivars was established to compare the responses of different specialty crop cultivars to sub-lethal doses of dicamba.A preliminary dose response with dicamba revealed 50% inhibiting doses (ID 50 ) of 76 g ae ha -1 and 255 g ae ha -1 for 'Mountain Merit' tomato and 'Crimson Sweet' watermelon, respectively.Tomato cultivars included 'Better Boy (Figure 1).', 'Brandywine Pink', 'Carolina Gold (Figure 1), 'Mountain Merit (Figure 1), 'Red Grape (Figure 1), 'Roma VF' and 'Super sweet 100 (Figure 1) while watermelon cultivars included 'Black Tail Mountain Organic', 'Crimson Sweet', 'Millionaire Figure 1, 'Sangria Figure 1 and 'Yellow Doll figure 1. Plants were grown until four true leaves developed and then treated with a range of dicamba doses (25.6 g ae ha -1 to 766.8 g ae ha -1 ).Visual injury was assessed at 7, 14 and 21 days after treatment (DAT), with plant dry weight determined at 21 DAT.Dry weight and visual injury data indicate that the range of tomato responses clearly fell into three groups: highly sensitive ('Roma'); moderately sensitive ('Better Boy', 'Brandywine Pink' and 'Super sweet') and sensitive ('Carolina Gold', 'Grape' and 'Mountain Merit').Visual injury data for watermelon revealed that all cultivars overall responded similarly.However, plant biomass of 'Millionaire' and 'Yellow Doll' were reduced by 25% compared to their untreated controls at a dose of 28 g ae ha -1 , while 'Black Tail Mountain', 'Crimson Sweet' and 'Sangria' dry weights required a dose of 250 g ae ha -1 to reduce biomass by 25%.Tomato and watermelon producers may consider selection of more tolerant cultivars in areas where the risk of off-target damage from dicamba exists.