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Ascochyta Blackspot Management in Brown Manure Field Peas

Ascochyta Blackspot, one of the major diseases of field peas, has been more prevalent in 2013 compared to recent years. This is due primarily to:

• Spore release from stubble residues is related to rainfall, particularly the number of rain days received. Dry conditions between August 2012 and March 2013, are likely to have led to a reduction in spore release from 2012 stubbles prior to 2013 pea crops emerging, hence increasing the amount of disease in April 2013 sown crops.

Rainfall through spring and summer will deplete the spore levels from previous field pea stubbles, resulting in much lower infection levels in the next crop.  This has been the case in years leading up to 2013.

The following strategies will reduce the impact of Ascochyta Blackspot in brown manure field peas:

• Avoiding sowing of field peas within 500 metres of one year old pea stubble, particularly on the eastern side.

• Not sowing field peas in a paddock more than once every 4 years, as Blackspot spores can survive for 3-4 years in the soil.

• As Blackspot levels increase rapidly in field pea crops during the flowering and pod fill stages, brown manure crops should be sprayed out prior to pods forming.

• If little or no rain is received between October and April, delaying sowing until May, will increase the likelihood of spore release occurring prior to new crops emerging.

• The responses to preventative fungicide strategies used in grain crops are highly variable and uneconomical for brown manure crops.

• A PreDicta B test for Blackspot in early autumn after a significant rainfall event, will help to determine the level of disease present, the results of which can be used to adjust sowing time.