WOUNDING CAN IMPROVE EFFICACY OF COLLETOTRICHUM ORBICULARE AS A MYCOHERBICIDE FOR BATHURST BURR

Colletotrichum orbiculare offers potential as a mycoherbicide for cont rol of Bathurst burr (Xanthium spinosum) but infection is restricted w here there are limited periods of free moisture on plant surfaces. Wou nding 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 wer e wounded by mowing or harrowing before application of C. orbiculare a t several spore dose rates. Harrowing plus spores caused a significant ly (P<0.05) higher mortality than spores alone in 3 out of 5 experimen ts. This effect of wounding did not occur for all spore dose rates app lied in individual experiments. In experiment 6, 2.5 x 10(11) spores/h a following harrowing were equally as effective in causing plant death as 5 x 10(11) spores/ha without harrowing. Mowing of plants was assoc iated with increased (P<0.05) mortality in 2 out of 3 experiments. Thu s, wounding can increase the efficacy of C. orbiculare but further stu dy is required to ellucidate the mechanism. The procedure may allow a reduction in quantities of mycoherbicide necessary for weed control.