'Wait and see' for stripe rust decision

The management of stripe rust in northern New South Wales is proving difficult due to the fact that wheat crops are at two vastly different growth stages, complicating decisions on fungicide use.

Stripe rust is widespread throughout northern NSW, with recent wet weather and milder temperatures resulting in an influx of reports from the Liverpool Plains through to Narrabri, Moree and Walgett.

NSW Department of Primary Industries plant pathologist, Steven Simpfendorfer, said decisions would need to be made on an individual crop basis factoring in growth stage, rust levels, potential yield and likely temperatures over the next few weeks.

“Most of the reports have occurred in the earlier sown wheat crops with only a few reports in later crops at this stage,” Dr Simpfendorfer said.

“Early sown crops are at full flag leaf emergence to heading, while crops established late due to weather conditions at sowing are much less developed - most at later tillering to early booting growth stages.

“Varieties with intermediate resistance such as Lang, Baxter and Sunco rely on adult plant resistance (APR) to combat stripe rust and this self-destruct mechanism expresses itself from full head emergence onwards.

“The earlier sown crops are at or very near this growth stage; however APR can be delayed in crops with higher nitrogen status.  This complicates decisions about whether to apply fungicides or not.”

Stripe rust basically impacts on yield and quality by reducing the green leaf area of the plant.   

This has led to debate as to the merits of using APR, which also results in further loss of green leaf area, to stop rust in these more advanced crops versus application of a fungicide.

Dr Simpfendorfer said APR was quite a useful defence mechanism but probably most effective at preventing new infections once it is activated in the plant rather than cleaning up moderate to high levels of infection which already exist in a crop.

“With the later sown crops it is really a matter of wait and watch over the next two to three weeks,” he said.

“These crops have reduced biomass which is less favourable to the cycling of stripe rust within a crop and lower potential yields which makes the economics of fungicide application marginal.

“Temperatures are also likely to rise in the next few weeks and this will have two effects on the pressure from rust.  Above 20 degrees stripe rust is not killed but simply cycles slower through plants hence the pressure from rust falls.

“Higher temperatures will also push the crop more quickly through its growth stages which also reduces the time that these intermediate varieties are at a susceptible growth stage.”

Further information on the management of stripe rust is available from NSW Department of Primary Industries or ‘Reference Point – Stripe Rust’ at www.grdc.com.au.

Media Contact:

Annette Cross, NSW DPI Tamworth 6763 1243, 0427 201 840