2017 canola blackleg sporacle forecasts are now available and some canola varieties have reduced blackleg resistance ratings
DAFWA's first blackleg spore showers forecast for the season is now available online.
Blackleg epidemics are primarily initiated by airborne ascospores originated from matured pseudothecia (fruiting bodies) of the fungus on previous years’ infected residues.
The DAFWA blackleg sporacle model predicts the onset of blackleg ascospore release from canola stubble for 25 canola growing districts of Western Australia.
The model is currently predicting that major spore releases are likely to coincide with the seedling establishment for the towns of Esperance Downs, Scaddan, Salmon Gums, Munglinup, Jerramungup, Mount Barker, Katanning and Darkan.
Early release of infective spores from old crop stubbles is anticipated to occur where there has been significant pre-seasonal rainfall coupled with cooler temperatures. Ravjit Khangura (DAFWA canola pathologist) encourages farmers in these areas to sow resistant varieties and plant canola at least 500m away from last year’s canola residues. Use of in-furrow and seed dressing fungicides are likely to be cost-effective in high disease pressure situations.
The model also shows that depending upon the rainfall events in the coming two weeks the fungal fruiting bodies may mature earlier in Narrogin, Williams, York and Northam. Therefore, the blackleg risk is considered above average in these areas and where possible farmers are encouraged to use resistant varieties and other blackleg management options.
In some Central and Eastern districts (Moora, Tammin and Merredin), the spore maturity is at a very early stage, therefore, the risk of infection on canola seedlings is low for the earlier sown crops.
In some of the central (Wongan Hills, Badgingarra) and northern areas (Northampton, Eradu, Mingenew and Mullewa), spore maturation process has not yet commenced, consequently, the risk of spores falling at the susceptible seedling stage is currently very low.
Refer to the Canola blackleg spore maturity forecast for Western Australia page to check the blackleg sporacle model forecast for other districts. The blackleg spore shower risk will change each week as the season progresses depending upon the weather conditions in the coming weeks, therefore, growers are urged to check the weekly updates.
The overall risk of blackleg infection on a property will be determined by factors such as choice of resistant variety, paddock rotation, fungicide usage, distance from previous year’s canola residues and stubble reduction.
Reduced resistance in canola varieties
The resistance ratings of some canola varieties have been downgraded due to their poor performance against blackleg in the majority of blackleg nurseries across Australia last year.
The triazine tolerant (TT) varieties ATR-Bonito, ATR-Wahoo and Pioneer 45T01TT are now rated moderately susceptible (MS) to blackleg in the latest GRDC Blackleg Management Guide. The Clearfield system varieties Pioneer 45Y88, Carbine and Archer are also now rated as MS to blackleg.
Growers who are planning to sow these varieties are urged to take extra care while implementing their blackleg management program.
Growers should consider;
- Sowing into paddocks that are out of canola rotation for more than three years.
- Avoiding sowing within 500m of last year’s canola residues.
- Applying seed dressing and fertilizer applied fungicide.
- Budgeting for foliar application in case it is required.
For further details on blackleg management and current blackleg ratings refer to GRDC’s Blackleg Management Guide (2017 Autumn variety ratings).
For more information contact Ravjit Khangura, Research Officer, South Perth on +61 (0)8 9368 3374.