Evaluation of the Response of Eight Tomato Cultivars to Early Applications of Uniconazole for Height Control in Containers

Excess elongation of tomato (Solanum lycopersicum L.) seedlings grown in containers for distribution to retail garden centers can impact market value.  Uniconazole is labeled for use on tomatoes in the United States at concentrations of 2-10 mg L^-1 when applied at the two to four leaf stage.  The objective of this work was to evaluate multiple cultivars to determine the response of earlier application times at lower concentrations.  The cultivars were Better Boy, Brandywine, Goliath, Homestead, Patio, Roma, Solar Fire, and Supersweet 100. Two trials were conducted in the spring of 2015 using 0.25 to 4.0 mg L^-1 applied 1 day after sowing the seed.  Spray volume was 300 ml m^-2.   Plant height data were taken 4 and 6 weeks after sowing.  Uniconazole reduced elongation of all the cultivars and the effect increased as concentration increased. There was a significant interaction between cultivar and concentration.  Patio has a naturally short habit and Uniconazole had greater effect on Patio compared to the other cultivars.  Supersweet 100 was less sensitive and about four times as much chemical was needed to achieve desired height control.  The other six cultivars had a generally similar response to Uniconazole and good height control was achieved with 0.25 to 1.0 mg L^-1.  These results indicate that commercial growers potentially can reduce the amount of chemical used on tomatoes with early application times.  For further work in spring 2016, Better Boy, Supersweet 100 and Patio were selected and Uniconazole is being applied at a range of application concentrations and times to compare the results of the early application strategy with the current label guidelines.