Following a high incidence of Ascochyta blight in 2016 chickpea crops throughout northern NSW and Queensland, there will be a large amount of ascochyta inoculum to infect 2017 chickpea crops. This inoculum will be present in three forms:
- Ascochyta infected chickpea residue being discharged out the back of headers or spread by floods and surface water;
- Seed internally infected by the fungus (a consequence of pod infection);
- Seed contaminated externally with infected chickpea residue during harvest and handling.
In order to reduce the occurrence and impact of Ascochyta blight in 2017 chickpea crops, the following strategies should be set in place. Some of these strategies are based on local and international field experiments, others are based on observations of reduced disease in 2016 crops. The more strategies employed the greater the benefit for chickpea growers in 2017 and beyond.
- Treat all seed: Proper treatment of seed with a registered fungicide will control both internally borne Ascochyta and external contamination.
- Grow varieties with improved Ascochyta blight resistance (experimental and observations): These varieties will have less disease and require fewer fungicide sprays. Current resistance ratings can be found here.
- Sow later in planting window (experimental and observations): This reduces the number of infection events.
- Sow on wider rows – 66cm+ (experimental and observations): Wide rows improve airflow through the crop leading to more rapid drying after a rain event or dew. They also delay canopy closure and improve penetration of fungicides later in the season.
- Double crop sorghum, cotton (experimental and observations): Stress and high biomass favour Ascochyta. Crops double cropped into sorghum or cotton residue in 2016 were less affected by waterlogging and did not produce the biomass of chickpeas sown into winter cereal or long fallow paddocks.
- Apply fungicide before the first post emergent rain event, even for PBA Seamer (experimental and observations): Crops that had an early preventative Ascochyta fungicide in 2016 had less disease than crops that were not sprayed until after the disease was detected. Even though PBA Seamer is rated resistant to Ascochyta, growers are urged to apply a preventative fungicide. This is because the large amount of inoculum from 2016 will increase disease pressure, and preventative sprays safeguard against changes in the Ascochyta pathogen that are more aggressive or virulent on PBA Seamer.
- Burn cereal stubble in paddocks intended for chickpeas (observations): Infected chickpea residue discharged during harvest of 2016 crops can blow onto paddocks that are intended for chickpeas in 2017; most of which will have had a cereal crop in 2016 (or 2015). The infected residues hold Ascochyta blight inoculum, providing a source of disease for the following chickpea crop.
- Tyne openers rather than disc (observations): Observations of less Ascochyta where crops had been sown with tynes in 2016 is thought to reflect burial and movement of Ascochyta inoculum away from the emerging seedlings.
By adding these strategies to an existing integrated management plan, the incidence of ascochyta may be greatly reduced. Using a combination of experimental and observational recommendations, it is possible to greatly reduce the chance of ascochyta infection from stubble borne inoculum and the resultant yield loss.