High blackspot risk forecast for South Australia in 2018

Page last updated: Thursday, 12 April 2018 - 3:01pm

Please note: This content may be out of date and is currently under review.

Early forecasts point to a high risk of blackspot in seedling field pea crops across most of South Australia in 2018. The extremely dry summer and autumn has delayed the maturation of blackspot spores on field pea stubbles. This means the spores will be released with rainfall in late autumn and winter, when the new crops are emerging and establishing. Growers should prepare for a high risk of blackspot establishing in their crops.

A number of actions can reduce this risk.

  • Growers should aim to plant this year’s crop at least 500m from field pea stubble, and if downwind from the stubble, where possible, increase this distance up to 1km since the spores are wind blown
  • In medium to high rainfall districts, the sowing date can be delayed 2-3 weeks past opening rains without compromising yield. The spore numbers in the air will reduce over the 2-3 week window and reduce the blackspot risk. However, delayed sowing is not an option in low rainfall short season districts as associated yield losses will be greater than losses caused by blackspot disease.
  • Fungicide strategies are an option in crops that have a yield potential of at least 1.5t/ha. P Pickel-T seed dressing will reduce infection on seedling crops, and foliar sprays of chlorothalonil will reduce the spread of the disease. Sprays can be applied between 4-8 nodes; apply at 4-node if disease is present but delay towards 8-node if disease is not evident. A second spray is at early flowering to reduce spread of the disease in spring. For maximum effect, spray ahead of a rain event, since spores are spread during rainfall. Post rain spraying is generally ineffective.
  • Note label restrictions for chlorothalonil with respect to grazing stock.
  • SARDI trials have shown that the foliar fungicide mancozeb reduces disease in some instances but is not always effective.
  • Other foliar fungicide products may become available during the season.

The risk identified in Blackspot Manager is associated with the number of spores released from last year’s stubble. Actual disease severity will also depend on rainfall patterns during crop establishment since moisture is necessary for the spores to germinate and infect the plants. Numerous rainfall events will increase disease severity, while few rainfall events will reduce disease severity.

For more information contact Dr Jenny Davidson at SARDI on ph +61 (0)8 8303 9389.