Australian growers in the northern grains region face tough year for yellow spot

Date:08-16-2011

With heavy stubble loads carrying yellow spot spores across the northern grains region, diligent crop monitoring will be on the cards for cereal growers this season.

Greg Platz, Department of Employment, Economic Development and Innovation (DEEDI) plant pathologist with Agri-Science says 2011 could be the worst disease year for more than two decades and proactive crop monitoring is the first step in disease management.

"The level of yellow spot infection is directly proportional to the quantity of infected stubble,” Mr Platz said.

"Growers should focus on reducing the amount of infected stubble, rotating paddocks to resistant crops, timely application of fungicides and sowing resistant varieties.”

He says there will undoubtedly be situations where wheat is sown into wheat stubble this season and the chance of yellow spot developing in these situations is high.

The only control method available post sowing is application of foliar fungicides, he said.

"It is important to understand that these are best applied as protectants and that they are not translocated from leaf to leaf.

"The level of control will depend on the number and timeliness of applications. It is not recommended that more than two applications of a fungicide be made in any season.”

Mr Platz said protecting the flag and flag-1 leaves was most important.

"Maximum yield and quality is gained by keeping the upper leaves free from disease during grain fill,” he said.

"For convenience this usually coincides with 90 per cent flag leaf emergence but may be delayed if epidemic progress is delayed.

"Growers should remember that one application will provide only 21 to 30 days of protection, depending on the rate of application.”

Mr Platz says the cost of fungicide should not be the main driver in choice of product or rate of application.

Grains Research and Development Corporation (GRDC)-funded DEEDI trials show the economic benefit of applying 500mL of propiconazole as opposed to half that rate.

In a trial situation using 2010 prices, this strategy returned an additional $260 per hectare.

"The choice of product and rate of application are secondary considerations, however both can strongly influence return on investment,” Mr Platz said.

"New vogue fungicides are typically admixtures of two chemicals having different rates of uptake and/or modes of action.

"They are more expensive than the single active product but may also give superior disease control and a better economic return.”

Mr Platz said propiconazole remains the standard for control of yellow spot and urged growers to plan for yellow spot control.

"Last year provided the most favourable conditions for the development of foliar diseases for 12 years which generated epidemics of yellow spot in wheat and spot form net blotch and leaf rust in barley,” he said.

"After several years of relatively low levels of these diseases, all factors contributing to epidemic development combined to initiate epidemics quite early in crop development.”