Yellow rust – an epidemic waiting to happen

Significant outbreaks of yellow rust (Puccinia striiformis) will occur in wheat crops next year, predicts Nickerson senior wheat breeder Bill Angus. From what he has seen in commercial crops and trial sites this season, he believes it is no longer a case of will yellow rust strike, but when.

“There is more yellow rust in crops now than I can remember for a very long time,” says Mr Angus. “The disease is cyclical and we expect to see raised levels every five to ten years – so the threat is not new.

“However, what is particularly worrying this time is how vulnerable many of the popular varieties are to this disease. In 2001/2002, 20% of the wheat crop was down to yellow rust susceptible varieties, and this year this figure has leapt up to 50%. Yellow rust susceptible varieties will have to be managed very carefully to achieve their full potential, and to avoid spreading the disease to neighbouring fields and beyond.”

Yellow rust epidemics, which can cut yields by up to 50% in untreated, highly susceptible varieties, usually begin in early May - depending on the temperature and how much inoculum is present in the juvenile crops. Once the first pustules are spotted in a susceptible variety the crop needs to be sprayed straight away.

“As we approach T2, farmers need to be walking their crops extensively to see what level of disease is lurking. Septoria is a big problem already, and growers should seek the advice of their agro-chemical specialists to help them through the rest of this season.”

When it comes to deciding which varieties to sow in the autumn, Mr Angus believes that growers in high risk areas should grow wheats they know won’t succumb to yellow rust. For example, Nickerson’s new biscuit wheat Nijinsky has a high level of resistance to all known races of the disease.

“Nijinsky is the only high yielding group 3 which is good against yellow rust and Septoria,” says Mr Angus. “In fact its resistance profile is impressive across the disease spectrum – scoring 8 for yellow rust, 6 for Septoria tritici, 7 for Septoria nodorum, brown rust and Fusarium, and 6 for eyespot and mildew.

“Farmers should see this level of in-built resistance as insurance - a way of getting out of jail should the weather turn bad, or something else happen which prevents fungicides being applied at the ideal time.”