Development of Cercospora leaf spot on Ipomoea weed species for biological control

Morning glories (Ipomoea spp.) are important weeds in non-burning sugarcane farming in Brazil, and their chemical control has low efficacy due to the straw mulching. The purpose of this work was to determine the effect of epidemiological parameters on the development of Cercospora leaf spot (Cercospora aff. canescens Ellis & G. Martin) on four Ipomoea weed species, as well as on the host range. The results demonstrated that the use of a suspension of 2 × 10⁷ conidia ml⁻¹ on specific host phenological stages (3–5 leaves, open flowers, and with fruit), with a minimum of a 24 h dew period, induces plant defoliation and a higher disease incidence on Ipomoea nil L. (Roth). However, the same disease incidence and defoliation on I. grandifolia (Dammer) O’Donell, I. quamoclit L., and I. hederifolia L. were not achieved. The pathogen was specific to these four Ipomoea species among 18 plant species. These results represent an important step in the development of a mycoherbicide to control morning glories.