Act now against future sunflower rust: MAFRI

The discovery of sunflower rust in some areas of Manitoba has prompted growers elsewhere to scout their fields for rust pustules. The dusty-brown-coloured rust on sunflowers will be visible on the leaves and stems.

Sunflower rust has the potential to occur every year in Manitoba. But the levels of infection and severity have been relatively low with the exception of a few localized hot spots in the central and southwest regions.

The last time the province experienced a severe infestation was in 2003 when a field survey determined infection rates ranged between trace amounts to more than 60 per cent of the leaf area affected by rust. Yields as well as seed weight and quality in the sunflower crop can be reduced at that level of infection. Before the growth stage R6 (disk flowers completed flowering, ray flowers wilting), rust will start impacting yield when three per cent of the plant’s upper leaves and bracts are covered with rust pustules.

However, the impact on yields and quality are reduced if rust occurs after the R6 stage. In most fields where rust has been seen this season, the rust has advanced into the overwintering stage, and is therefore not continuing to spread.

While the potential for yield and quality reduction are worrisome for both producer and processors, there are no fungicides registered in Canada for control of sunflower rust. Producers can, however, use cultural practices to reduce the risk of future infections.

  • Avoid planting sunflowers adjacent to a previously heavily infected sunflower field;
  • Use a one-in-three-year rotation for sunflower fields;
  • Seed as early as possible after the risk of frost is past;
  • Control volunteer and wild sunflowers growing around commercial fields;
  • Follow recommended planting rates to avoid high plant populations and high nitrogen rates, which lead to dense canopies that favour disease;
  • Choose a variety with better resistance. Resistance ratings for rust are published in Seed Manitoba.

— Article courtesy Manitoba Agriculture, Food and Rural Initiatives (MAFRI).

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