Effects of some environmental conditions on the effectiveness of Drechslera avenacea (Curtis ex Cooke) Shoem.: a potential bioherbicidal organism for Avena fatua L.

Drechslera avenacea is a potential bioherbicide for Avena fatua, wild oat, control in dryland wheat crops in southern Australia. Maximum disease severity (DS) (1.1 lesions per mm2 of leaf tissue) was recorded following application of 1×105 spores per ml and exposure of weeds to a 12- to 16-h dew period at 20–25 °C. Weed seedlings between 3 and 5 weeks of age were the most susceptible to the disease. Occurrence of a low humidity (<50% R.H.) for up to 8-h before the initiation of a dew period following inoculation did not reduce subsequent DS. Repeated 8-h (suboptimal) dew periods increased DS when compared with a single 8-h dew period (0.26 lesions per mm2 compared to 0.39 lesions per mm2, respectively). This was not the case for repeated 6-h dew periods. Following inoculation, temperature had a direct effect on disease development rate. Plants recovered following inoculation and inoculated and uninoculated plants were not significantly different in terms of necrotic leaves 28 days after inoculation. Dew period limitations and the ability of D. avenacea to indirectly create a competitive advantage for wheat seedlings over wild oat are discussed in relation to the feasibility of this bioherbicide agent.