Reports of growers treating stripe rust in moderately resistant wheat varieties have sparked significant concern from leading cereal pathologist, Dr Steven Simpfendorfer.
Dr Simpfendorfer, NSW Department of Primary Industries research scientist, Tamworth, NSW leads Grains Research and Development Corporation (GRDC) supported pathogen research and says poorly considered advice is costing the grains industry millions of dollars.
“Stripe rust is a virulent disease which needs to be managed – but only in varieties which have insufficient disease resistance,” Dr Simpfendorfer said.
“There have been a number of reports of growers being advised to treat stripe rust and apply a fungicide to wheat varieties that are moderately resistant to stripe rust to “preserve green leaf area”.
“This practice is costing the industry millions of dollars in unnecessary sprays as well as placing pressure on the longevity of our most effective, reliable and cheapest fungicides.”
Dr Simpfendorfer says there is no evidence that spraying moderately resistant varieties for stripe rust will result in any return on input cost for growers.
“There is no effect on a moderately resistant variety in fighting stripe rust even under heavy disease pressure situations such as at North Star in the very conducive 2011 season,” Dr Simpfendorfer said.
“Fungicides are not cheap insurance. They are very effective chemicals when used in the right situations.
“The unnecessary use of fungicides simply because they have become so cheap in recent years is inevitably going to lead to fungicide resistance in the future in some of our common fungal pathogens of wheat.”
Dr Simpfendorfer said replicated trials conducted across 13 sites in central and northern NSW by NSW DPI and GRDC in 2011 have consistently shown no significant yield improvement by spraying moderately resistant varieties such as EGA Gregory.
The trials were located at GRDC-funded National Variety Trial (NVT) sites. Twelve rust management strategies using seed treatment options or in-crop sprays were evaluated across a moderately susceptible variety, Ellison, and a moderately resistant variety, EGA Gregory.
Yields ranged from 1.5 tonnes per hectare to 7t/ha. The response to stripe rust treatments under low and high stripe rust pressure was evaluated.
“Low disease pressure occurred at six sites and resulted in no yield response to applied fungicide even in the moderately susceptible variety,” Dr Simpfendorfer said.
“Under high disease pressure where more than 50 per cent of the top three leaves were covered with stripe rust, such as at the North Star site, the moderately susceptible variety Ellison lost 45pc of its yield when stripe rust was not controlled at all.
“In contrast, the moderately resistant variety EGA Gregory experienced no yield loss (5.7t/ha) when no fungicide sprays were applied compared to two in-crop fungicide applications at Z32 and Z39 (5.7t/ha).”
Growers are advised to check the resistance rating of their wheat varieties and to use this information when determining if a fungicide spray is necessary for managing stripe rust.
A full Report is available at http://www.dpi.nsw.gov.au/__data/assets/pdf_file/0017/431270/Fungicide-management-of-stripe-rust-in-wheat.pdf
For more information on GRDC-funded research, visit www.grdc.com.au.
PHOTO CAPTION: Dr Steven Simpfendorfer, NSW DPI, Tamworth, NSW says growers should consider rust ratings before treating cereal crops for stripe rust.
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