Blackspot Disease Forecast 2023

SARDI Crop Watch has released its Blackspot disease forecast with an indication towards a ‘highly variable risk’ of blackspot disease of seedling field peas that…

May 9, 2023Agronomics Back to All

SARDI Crop Watch has released its Blackspot disease forecast with an indication towards a ‘highly variable risk’ of blackspot disease of seedling field peas that are sown from late in April through to early May across SA. Some of our areas are considered to be at a higher risk, and some are considered low.

Do you need to worry?
No, not yet. Wait and see what the rain brings. As you know, the severity of the disease depends on the rainfall patterns which occur throughout crop establishment – the spores need moisture to germinate and then infect the plants.

Numerous rainfall events = increase in the severity of the disease. Minimal rainfall = disease suppression, irrespective of the number of spores released.

What can you do to mitigate the risk?
PIRSA and SARDI recommend several mitigation strategies that can be implemented to reduce the risk of infection.
They include:

Sow at least 500 meters away from old stubbles. (Increase to 1 kilometre if downwind of the stubble, as the spores are windblown).
Delay sowing 2-3 weeks after the break can benefit medium to high rainfall areas. Spore numbers will decline over time. (Not recommended in lower rainfall areas as the late sowing may cause a greater reduction in yield than the blackspot disease).
Use seed dressings to reduce infection, such as thiram and thiabendazole (P Pickel T)
Fungicide strategies are viable where the crop has a yield potential of at least 1.5 tonnes. Use foliar sprays to reduce disease spread. Sprays can be applied between 4 to 8 nodes. If the disease is present, it is recommended to apply at 4 nodes. If it isn’t present, then delay to 8 nodes. Spraying again at early flowering is required in order to reduce the disease spreading in spring. Spraying ahead of a rain event is also recommended as this is when spores are spread. There are a number of products that have been registered for use in the control of blackspot in field peas.
Other control measures include removal of self-sown plants, implementing crop rotations, using disease-free seed and use of varieties that display resistance.