Volunteer plants increase disease risk

Higher than average rainfall across many parts of the state during March and April has led to an increase in volunteer (self-sown) plants. As a result, significant 'green bridges' have been reported in key grain-growing regions, although other areas are also likely to be affected.

Green bridges formed by volunteer plants or plant material along roadsides and paddock margins can increase disease and pest risks early in the growing season.

Growers should be aware of stubble-borne diseases developing on volunteers, including barley net blotches (net form net blotch and spot form net blotch) and scald, Ascochyta blight and Botrytis grey mould in lentil as well as wheat diseases such as Septoria tritici blotch and powdery mildew. Infection on volunteer plants can increase inoculum levels early in the season and drive disease epidemics through elevated spore loads within regions.

Although stripe rust levels in South Australia were low last season, the increased presence of green bridge poses a heightened risk for disease carryover into 2026, and growers should remain vigilant.

Effective green bridge control is critical:

• Volunteer plants and weeds should be removed at least 2 to 3 weeks prior to sowing.
• In areas with a well-established green bridge, early crop monitoring will be essential to support timely and effective disease management decisions.

See Green bridge for more information on green bridge control and the associated pest and disease risks.