| Summary: | Greenhouse and field experiments showed that conidia of the fungal pathogen, Phoma commelinicola, exhibited bioherbicidal activity against spreading dayflower (Commelina diffusa) seedlings when applied at concentrations of 106 to 109 conidia·mL−1. Greenhouse tests determined an optimal temperature for conidial germination of 25 °C–30 °C, and that sporulation occurred on several solid growth media. A dew period of ≥ 12 h was required to achieve 60% control of cotyledonary-first leaf growth stage seedlings when applications of 108 conidia·mL−1 were applied. Maximal control (80%) required longer dew periods (21 h) and 90% plant dry weight reduction occurred at this dew period duration. More efficacious control occurred on younger plants (cotyledonary-first leaf growth stage) than older, larger plants. Mortality and dry weight reduction values in field experiments were ~70% and >80%, respectively, when cotyledonary-third leaf growth stage seedlings were sprayed with 108 or 109 conidia·mL−1. These results indicate that this fungus has potential as a biological control agent for controlling this problematic weed that is tolerant to the herbicide glyphosate.
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