Influence of Spore Dose and Water Volume on a Mycoherbicide′s Efficacy in Field Trials

Colletotrichum orbiculare is a potential mycoherbicide agent for control of Xanthium spinosum (Bathurst burr: spiny cocklebur). Applications of conidia at a range of doses in 3 water (carrier) volumes, plus and minus oil as an adjuvant, were assessed in field trials. Spore doses of 1010 or 1011 conidia/ha generally gave inadequate control but higher doses of 2.5 × 1011, 5 × 1011, and 1 × 1012 conidia/ha provided satisfactory control where environmental conditions were conducive to anthracnose development. High carrier volumes of 1000 liters/ha were generally not superior to volumes of 500 and 250 liters/ha. Oil as an adjuvant did not enhance infection. Results were inconsistent but best weed control was obtained when the mycoherbicide was applied to young, actively growing plants during long dew periods in spring or early summer.