Wounding can improve efficacy of Colletotrichum orbiculare as a mycoherbicide for Bathurst burr

Abstract

Colletotrichum orbiculare offers potential as a mycoherbicide for control of Bathurst burr (Xanthium spinosum) but infection is restricted where there are limited periods of free moisture on plant surfaces. Wounding of plants ruptures cells and releases moisture and/or nutrients which may enhance infection. Wound sites may also offer easier access to the fungus. In 7 field trials over 2 seasons at 4 sites, plants were wounded by mowing or harrowing before application of C. orbiculare at several spore dose rates. Harrowing plus spores caused a significantly (P<0.05) higher mortality than spores alone in 3 out of 5 experiments. This effect of wounding did not occur for all spore dose rates applied in individual experiments. In experiment 6, 2.5 x 1011 spores/ha following harrowing were equally as effective in causing plant death as 5 x 1011 spores/ha without harrowing. Mowing of plants was associated with increased (P<0.05) mortality in 2 out o f 3 experiments. Thus, wounding can increase the efficacy of C. orbiculare but further study is required to ellucidate the mechanism. The procedure may allow a reduction in quantities of mycoherbicide necessary for weed control.