In years with summer rain, WA grain growers face a weed burden that acts as a "green bridge" or "hotel" where pests and diseases survive over summer until more plant material is available in the form of new crops.
Geoff Thomas, Grains Research and Development Corporation (GRDC) supported plant pathologist at the Department of Agriculture and Food WA (DAFWA), says growers should plan to manage the cereal rust risks associated with summer rain and cereal regrowth this season.
DAFWA will survey the green bridge development leading into the cropping season, including conducting a statewide 'Green Bridge Survey Day' on Tuesday, March 17.
Mr Thomas encouraged growers to be vigilant as barley leaf rust and wheat stem rust were discovered on regrowth in December and January, indicating rust was carried over late last season.
He says eastern states growers faced one of the most intensive stripe rust epidemics in 30 years in 2008.
Dr Rohan Rainbow, GRDC manager of crop protection, says eastern states growers spent an estimated $45 million on chemicals to combat the epidemic, adding substantially to losses already incurred from the disease.
But WA growers can learn from this.
Wheat can be infected by three predominant rust species: leaf, stem and stripe rust. Rust spores are not carried on seed or stubble, but require living hosts to survive, making cereal regrowth a major green bridge risk for cereal rusts.
Mr Thomas says maximising the pre-sowing fallow period with early weed control with herbicide or grazing, rather than delaying sowing, will reduce rust and pest activity before planting.
Spraying weeds and cereal regrowth to conserve soil moisture will also help manage the green bridge.
Points to remember:
• weeds are more readily controlled when small;
• grazing may assist weed control if compatible with other farming practices; and
• report green bridge rust infections to your local DAFWA office.
Although too early to definitively predict what will happen, continuing rain will maintain the risk associated with green bridge hosted diseases and, conversely, with a dry finish to summer and a late break, the impact of the green bridge could reduce.