Herbicide efficacy, leaf structure, and spray droplet contact angle among Ipomoea species and smallflower morningglory

Greenhouse and laboratory studies were conducted to evaluate responses of ivyleaf morningglory, pitted morningglory, palmleaf morningglory, and smallflower morningglory to several herbicides in relation to leaf structure, epicuticular wax, and spray droplet behavior. Two- to four-leaf stage plants of each species were highly susceptible to acifluorfen, bentazon, bromoxynil, glufosinate, and glyphosate. However, at the five- to eight-leaf stage, these species were less susceptible, and control was herbicide specific. Spray droplets of these five herbicides had a higher contact angle on ivyleaf morningglory than the other three species with a few exceptions. Stomata and glands were present on both adaxial and abaxial leaf surfaces of all species, and palmleaf morningglory and smallflower morningglory had more of these than did the other two species. Trichomes were present on all species except palmleaf morningglory. Epicuticular wax mass was highest in ivyleaf morningglory (57 μμg cm⁻⁻²) and lowest in smallflower morningglory (14 μμg cm⁻⁻²). Wax consisted of homologous short-chain (< C₁₈) or long-chain (> C₂₀) hydrocarbons, alcohols, acids, and triterpenes. Smallflower morningglory waxes lacked short-chain length components. Triterpenes were absent in palmleaf morningglory and smallflower morningglory epicuticular waxes. Untriacontane (C₃₁ hydrocarbon) and tridecanol (C₃₀ alcohol) were common major long-chain components in waxes of all four species. Heptadecane (C₁₇ hydrocarbon) and octanoic acid (C₁₈) were common major short-chain length wax components in pitted, ivyleaf, and palmleaf morningglory. In spite of some differences in leaf surface structures, wax mass, and wax components among the four species, there was no clear relationship between these parameters and herbicide efficacy.Nomenclature: Acifluorfen; bentazon; bromoxynil; glufosinate; glyphosate; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. IPOHE; palmleaf morningglory, Ipomoea wrightii Gray IPOWR; pitted morningglory, Ipomoea lacunosa L. IPOLA; smallflower morningglory, Jacquemontia tamnifolia (L.) Griseb. IAQTA.