Northern New South Wales graingrowers thinking about using fungicide against stripe rust in their wheat crops have a couple of issues to consider before they fill the spray tank.

New South Wales Department of Primary Industries (NSWDPI) cereal pathologist Steven Simpfendorfer says growers and their advisers have to balance the cost and likely effectiveness of spraying against questions of varietal susceptibility, estimated crop yield and the availability of fungicides.

"We know stripe rust is pretty widespread in northern New South Wales, even though the weather wouldn¹t appear to have been exceptionally conducive to its development," Dr Simpfendorfer said.

"Obviously there still must have been enough humidity in the crop canopy to get it going.

"As we get into the later stages of crop development, the economy of spraying becomes questionable. We have to ask whether there is any great advantage in keeping all of the flag leaf green for another few weeks, and whether there is likely to be a lot of associated yield benefit.

"Many crops in northern parts of the state are rapidly getting beyond the stage of growth where spraying is likely to be cost effective, and many of them are starting to see the effect of the adult plant resistance to stripe rust that is incorporated in the majority of northern wheat varieties and becomes active after head emergence."

Dr Simpfendorfer said tissue death around rust pustules showed adult resistance was working.

Scouting a crop early in the morning would also allow growers to determine whether stripe rust was still active, because new pustules were yellow when freshly produced overnight.

Pustules became orange as they aged and dried during the day, and could have been produced some time ago.

Dr Simpfendorfer said spraying might be warranted in areas like the Liverpool Plains and south from there, where adult plant resistance had not become active yet, because crops were at earlier growth stages.

Even so, given the shortage of fungicide ­ caused by much of Australia¹s stocks being diverted to Western Australia because of major rust outbreaks there ­ growers had other issues to consider.

They might have to restrict themselves to spraying a limited number of paddocks, and considerations in that situation should be potential yield, growth stage, rust severity and varietal susceptibility to stripe rust.


Saving 10 per cent of a potential yield of four tonnes made much better financial sense than saving 10 per cent of a two tonne crop.

There was a wealth of information about stripe rust available to growers and advisers on the Grains Research and Development Corporation (GRDC) GrainZone website www.grdc.com.au, including all papers from the July round of cereal leaf disease workshops. Advice on a disease response scale used by the Australian Cereal Rust Control Program could be found on http://www.grdc.com.au/growers/as/stripe_rust2.htm