Tell-tale brown bridge spreading through south
By COLIN BETTLES
A RUST epidemic is threatening to further reduce the state's drought-stricken grain supply this harvest.
New rust infections including stripe, leaf and stem rust have been discovered in the south-eastern Wheatbelt and along the south coast and, according to the experts, are moving with increasing frequency in those locations.
With the drought already depleting WA's grain production by at least half this season, experts have warned growers to be vigilant in protecting themselves against the risk of further crop damage from the spreading disease.
Co-operative Bulk Handling (CBH) has forecast that between six and nine million tonnes of grain will be received this harvest, but that estimate could be reduced by at least one million tonnes depending on factors including reduced rainfall and increased disease.
Worst hit will be the Geraldton zone, which after a record return last harvest, is set to drop by 80pc to somewhere between 500,000t and 700,000t of grain.
While the Esperance zone is set to generate a near-record return of between 1.8 and 2.2 million tonnes, the Albany and Kwinana zones are also forecasting well below-average returns.
After CBH received 12.5 million tonnes of grain last year, this season's loss in grain production is set to cost the grain handling giant an estimated $50 million in revenue.
Agriculture Department grains industry development director David Bowran has already said WA's final production figure was almost certain to be reduced by several factors apart from the drought.
"Most years at least one of these other factors including frost, rust, locusts, weather damage and high temperature at grain filling has had an impact on grain production," Mr Bowran said.
While recent rains have helped prevent further decline in CBH's current grain estimates, the damp conditions have generated another threat with fertile breeding conditions attributing to the increased threat of rust disease.
Last week's PestFax reported stripe rust sightings from growers and agronomists across the state.
PestFax, which reports on diseases and pests threatening crops and pastures throughout WA's grain belt, confirmed stripe rust had been found in a Calingiri wheat crop at stem elongation stage, in crops south of Shackleton.
The disease was also reported in Wyalkatchem and Stiletto wheat crops on a farm south of Needilup.
To the north, south and west of Lake King stripe rust was also found in advanced crops sown in the first week of May, with some showing early flag leaf emergence.
Stem rust and leaf rust had also been reported in a Yitpi wheat crop at about the five leaf growth stage south-east of Hyden.
Danger signs were at their highest for crops around Esperance, Munglinup, Cascade, Grass Patch and Scaddan where the disease had been spreading rapidly in crops from early stem elongation through to early flag leaf emergence.
Agriculture Department plant pathologist Geoff Thomas said stripe rust was moving with increasing frequency in the areas where it was originally found and was now spreading rapidly in the Esperance and south-east Wheatbelt regions.
Mr Thomas said reports of the disease in other areas indicated it would pose a serious threat to many crops across the state.
"The disease is obviously a concern for many wheat growers who had a poor or late start to the season and have many crops with lower than usual yield potential," Mr Thomas said.
"One of the major issues with stripe rust is that it is being found in crops which are at relatively young growth stages, so in many cases it will probably require some fungicide management.
"Generally it is being found in the earlier sown crops, but with favourable conditions we can expect it to start appearing in later sown crops as the season progresses."
Mr Thomas rated the potential for crop damage as quite high.
"Due to the fact that infection has happened quite early in the crop's growth, there is a significant amount of time remaining in the season for the disease to spread within crops and across farming regions," Mr Thomas said.
"The current damp weather is good for crops, but also provides ideal conditions for the spread of stripe rust.
"How the stripe rust epidemic progresses is very dependant on seasonal weather conditions.
"With ongoing rain and favourable conditions we can expect the disease to continue to spread, however, if the season dries off then this will curtail the spread and impact of rust.
"Stripe rust can cause significant yield losses - its impact will be greatest in crops where infection occurs early and in susceptible varieties.
"Stem rust has also been noted in cereal regrowth and some young crops in a number of areas.
"If these areas have a warm moist spring stem rust could also be an issue for wheat growers."
Mr Thomas said early detection and control of stripe rust would go a long way towards reducing the risk of serious crop damage this season.
"Growers need to be aware of rust occurring in their region and carefully monitor their own crops for presence of the disease," he said.
"In the early stages of crop development it is likely that application of fungicide will be beneficial in infected crops to manage the disease.
"Later in the season management of disease will depend on a number of factors including the growth stage of the crop, amount of rust in the crop, the variety resistance, seasonal weather outlook and recent weather conditions, yield potential of the crop and the cost of management of the disease."
Agriculture Department Great Southern district manager Jon Glauert said frost was the biggest threat to this season's crop.
Despite the risk, Mr Glauert said the late season break could provide growers with an unexpected advantage.
"We may be lucky with the later planting and germination and we could miss the most dangerous frost period in September when crops are usually flowering because flowering should be later this year," Mr Glauert said.
Landmark Esperance agronomist Karina Zacher said while stripe rust had been reported in the majority of her region, it had only affected Annuello, Bonnie Rock, Janz, Stilleto, Sapphire, Mitre, Wyalkatchem and H45 wheat varieties.
"Up until a week ago sightings of stripe rust were confined to crops that did not receive Jockey or Impact at sowing, however, it has now been reported in crops that did receive a seed or in-furrow treatment at sowing," Ms Zacher said.
"Growers have received excellent protection against stripe rust from these seed and in-furrow treatments, Jockey and Impact, which in many cases has enabled crops to reach at least flag emergence before they need spraying."