Myrothecium verrucaria for Control of Annual Morningglories in Sugarcane

Conidia of Myrothecium verrucaria, sprayed in an aqueous phase-paraffinic crop oil emulsion (1:1 v/v) at 470 L/ha, controlled red, ivyleaf, smallflower, and tall morningglory plants (three- to five-leaf stage) by causing severe necrotic injury to leaves and stems. Conidia were not efficacious if applied in an aqueous carrier without oil. When applied in the field as directed postemergence treatments to sugarcane, a concentration of 4 x 10⁸ conidia/ml generally provided >90% death of morningglory, comparable with the atrazine standard at 2.2 kg ai/ha, and did not cause significant crop injury. Conidia produced on potato dextrose agar or rice flour slurry were about equally effective. When killed by autoclaving, conidia continued to be efficacious, indicating that the symptoms produced by the fungus were not primarily caused by infection. A high performance liquid chromatography analysis of filtrates from the fungal growth media or of harvested conidia showed the presence of several macrocyclic trichothecenes (MT), some known to be phytotoxins. These included verrucarin A and H, roridin A and H, and isororidin E for filtrates and verrucarin A and roridin A for conidia. However, only trace amounts of MT were detected in leaves of treated morningglory plants at 24 h after treatment and none at 48 and 96 h even though the fungus was isolated from leaves up to 14 d after treatment. Further study is needed to identify the causal agents responsible for the phytotoxicity produced by M. verrucaria and to assess potential of this organism as a mycoherbicide.