The present invention discloses fungal isolates of Phoma macrostoma or extracts obtained therefrom, useful for the control of broad leaf weeds, including Canada thistle, perennial sowthistle, dandelion, scentless chamomile, false cleavers, chickweed, wild buckwheat, and field bindweed. The present invention also discloses biological control compositions comprising fungal isolates formulated in a growth medium for maintaining the viability of the fungal isolates when the biological control composition is applied to soil. The present invention also discloses a novel probe and primer pair sequence for use in detecting Phoma macrostoma isolates that exhibit biocontrol activity. The present invention also discloses methods of screening fungal isolates to determine if they exhibit biocontrol activity.