2017 ASHS Annual Conference

Ethephon is a widely used growth regulator in outdoor food crop production to elicit a range of plant responses and in greenhouses to control containerized crop growth. The objectives of this study were to quantify the effectiveness of ethephon foliar sprays on controlling growth of containerized vegetable and herb bedding plants. In Expt. 1, seedlings of ‘California Wonder’ pepper (Capsicum annuum L.), ‘Rutgers’ tomato (Solanum lycopersicum L.), ‘Italian Large-leaf’ sweet basil (Ocimum basilicum L.), and flat-leaf parsley (Petroselinum crispum (Mill.) Fuss.) were sown in 288-cell plug trays. Seedlings were planted into 10-centimeter-diameter containers filled with soilless peat-based substrate four weeks after sowing and grown in a glass-glazed greenhouse. One week after transplanting seedlings, plants were treated. Foliar sprays of solution containing 0, 125, 250, 500, 1000, or 2000 mg∙L^–1 ethephon. Four weeks after transplanting seedlings, data were collected on plant height, diameter, and shoot dry mass (SDM). In Expt. 2, pepper and tomato seedlings were transplanted and grown as described for Expt. 1. Foliar sprays containing 0, 250, 500, 750, or 1000 mg∙L^–1 were applied once (1 week after transplanting) or twice (1 and 2 weeks after transplanting). Plant culture, growing environment, and data collected were as previously described. As ethephon concentration increased to 1000 mg∙L^–1 in Expt. 1, tomato were 21.7 cm (63%) shorter than untreated plants; increasing ethephon to 2000 mg∙L^–1 provided no additional height control. Tomato diameter and SDM were increasingly suppressed as ethephon increased up to 1000 mg∙L^–1. Pepper responded similarly to tomato, though the magnitude of suppression was less. Height and width of basil and parsley, respectively, were minimally affected to ≤ 500 mg∙L^–1 ethephon. Phytotoxicity was observed for plants treated with 2000 mg∙L^–1 ethephon for all four species. In Expt. 2, growth responses to ethephon spray concentration were similar to the trends observed in Expt. 1. As ethephon concentration increased for single or multiple applications, plant growth (height, diameter, and SDM) was less for both tomato and pepper. While a second ethephon application increased control of tomato growth, a second spray conferred minimal additional control for pepper. As ethephon concentration increased, tomatoes stems were less upright, presumably from diminished rooting. While it suppressed height, diameter, and SDM of containerized tomato and pepper, the utility of ethephon as a growth retardant for containerized vegetable plants may be limited.