Effects of Myrothecium verrucaria on morning-glory (Ipomoea) species

During field testing of a bioherbicidal strain of the fungus Myrothecium verrucaria (MV) for control of spurges and purslanes in tomato test plots in summer of 2005, we noted extensive damage to volunteer morning-glory (Ipomoea spp.) seedlings. This observation prompted investigations on the biological control efficacy of MV on various Ipomoea species under a controlled environment. Seven morningglory species [ivyleaf (Ipomoea hederacea), moonvine (Ipomoea turbinate), palmleaf (Ipomoea wrightii), pitted (Ipomoea lacunosa), multi-color (Ipomoea tricolor), moonflower (Ipomoea alba), and cypressvine (Ipomoea quamoclit)] were grown in greenhouse and tested at first to second leaf growth stage. MV spores (10⁷spores mL ¹) were formulated in Silwet L-77 surfactant (0.2%, v/v) or an invert emulsion containing this surfactant. Plants were treated either with Silwet (0.2%, v/v) alone (control), invert emulsion plus Silwet, MV plus Silwet, or MV plus Silwet plus invert emulsion via spray application. After application, the plants were placed in a dew chamber (15–18 h) and then transferred to a greenhouse. Plant injury and disease progression were assessed visually and fresh and dry weights were determined at the end of tests (7 days after treatment). Some of these species exhibited more tolerance than others to spray applications of MV plus Silwet, depending on the time after treatment. Compared to MV alone treatments, formulations of MV plus the invert emulsion promoted injury symptomology in pitted and moonvine morning-glories, but caused less disease symptomology than MV alone in palmleaf seedlings. There were no significant differences in disease symptomology of the MV alone and MV plus invert treatments in the other species. Overall, the results indicate some differential injury effects of MV on closely related species, i.e., Ipomoea (morning-glories), and that the invert emulsion can increase the efficacy of MV in certain instances.