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Controlling Stripe Rust in Dual Purpose Wheat

04 June 2012
GRDC

AUSTRALIA - The high incidence of stripe rust in dual purpose cereal crops has prompted calls for growers to consider varieties with higher rust resistance ratings.

Dr Rohan Rainbow, Grains Research and Development Corporation (GRDC) senior manager, plant health says there are good varieties available with excellent rust ratings.

“Rust resistance is particularly important when growing long season cereals as they enter the “green bridge” danger period when rust spores can be over-summering on weeds and volunteer cereal plants,” Dr Rainbow said.

With severe and early onset of stripe rust costing grain growers up to 45 per cent of yield in moderately susceptible wheat varieties, new research is exploring grazing and fungicidal control measures.

Maurie Street, Grain Orana Alliance (GOA) chief executive officer is leading research into the effect of grazing dual purpose wheats in central west NSW.

“One of the greatest shortcomings of current dual purpose wheat varieties being selected and grown by central west NSW growers is the inability to couple high quality grain with good levels of stripe rust resistance,” Mr Street said.

“Lower resistance and the longer growing season of these varieties could expose these varieties to even higher damage than their shorter season counterparts.

“Of more concern to some growers is the haven that these varieties form to harbour and breed up the disease to wreak havoc on neighboring wheat crops in the spring.”

The current recommendation of grazing is common for infected dual purpose crops that are infected with stripe rust in the autumn, Mr Street said.

He says grazing helps control rust through two pathways:

  • Removal of the inoculums via grazing of the infected material and inoculum sources for subsequent infections.
  • Opening the crop canopy to accommodate better airflow and circulation, which reduces disease development by lessening the extent and length of time the leaves are wet.

Mr Street says the GRDC-supported research shows grazing can have a significant impact up to 0.5 tonnes per hectare but can be either positive or negative.

“Over two seasons the impact of grazing has been variable,” Mr Street said.

“In 2010, which was a very wet year, grazing had a positive impact upon yield up to 0.5t/ha.

“But in contrast in 2011 (quite a dry year) grazing had a negative impact upon yield of 0.45t/ha which is counterintuitive to what we would predict.”

Mr Street said while the results were based on limited trials and seasons and in these two trials where Jockey® seed treatment was used on Wedgetail dual purpose wheat it did not delay stripe rust onset or offer any yield or quality advantages over standard seed treatments in two trials over two seasons.

“However these trials were sown in late April/early May, in both situations where there was minimal early season infection,” he said.

“In 2010 there were significant spring infections of stripe rust pathogen and in 2011 the infection at any stage was negligible.”

Mr Street said one of the most interesting outcomes in both trials was the positive response in yield to application of fungicides just prior to grazing.

In both years there was a negligible level of leaf disease at the timing of this application yet the crop responded to the fungicide, he said.

“We are unsure why the crop responded when there was no apparent disease,” Mr Street said.

“The trials indicated yield impacts from grazing were most likely not related to any level of stripe rust control but more to do with the effect of grazing on the crop canopy and water use efficiencies.”

He says this makes sense as no major yield-contributing leaves such as the flag leaf are present during the autumn period so this discounts the possibility of yield loss from autumn disease.

“Defoliation though disease or grazing at these stages was not hugely detrimental to yield otherwise dual purpose crops would not be as successful as they are,” he said.

“Unfortunately these results do not encourage growers to control autumn infections of stripe rust, which could be having a much higher hidden cost.

“Increases in overall disease level and pressures in the whole community increases the likelihood of a resistant strain developing and increasing control costs over all wheats – grazed or not.”

Mr Street says a recent reduction in the labeled grazing withholding period of Intake® in-furrow will allow for use in dual purpose crops.

This use may improve autumn control of the disease over that of the previous standards, he said.

“This new option now gives growers the motivation to have an autumn control measure in place reducing the resistance threat to the whole industry.

“Improved varieties however coupling good milling quality grain with increased resistance in a dual purpose wheat will be the best outcome though.”

TheCropSite News Desk

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