Tolerance of Selected Bedding Plants to Four Herbicides In Irrigation Water

Begonia (Begonia semperflorens ‘Cocktail Whiskey’), vinca (Catharanthus roseus ‘Sun Devil Extreme’), melampodium (Melampodium paludosum ‘Million Gold’) and impatiens (Impatiens walleriana ‘Super Elfin’) were irrigated with water treated with quinclorac, topramezone, imazamox and penoxsulam to identify herbicide concentrations that cause phytotoxic effects. Plants were irrigated four times over a 10-day period with the equivalent of 1.27 cm of treated water during each irrigation, then irrigated with tap water until they were harvested 28 days after the first herbicide treatment. Visual quality and dry weight data revealed that melampodium was the most sensitive of the bedding plants to quinclorac, imazamox and penoxsulam, whereas vinca was the most sensitive species to topramezone. Noticeable reductions in visual quality and dry weight of melampodium were evident after exposure to 240, 580 and 10 ppb of quinclorac, imazamox and penoxsulam, respectively, while dry weight of vinca was reduced after exposure to 110 ppb of topramezone. Current irrigation restrictions on imazamox, penoxsulam and topramezone are adequate to minimize damage to these bedding plants if herbicide-treated waters are used for four irrigation events. However, irrigation restrictions should be established for quinclorac to prevent damage to sensitive bedding plants such as vinca.