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You are here: Agriculture » About Agriculture » Newsletters and Updates » Ag in Focus » Ag in Focus - Winter 2011 » Wettest summer heightens disease threat

Wettest summer heightens disease threat

DPI senior plant pathologist Grant Hollaway

At a glance

• Potential for diseases in cereal crops highest in 30 years.
• Farmers urged to monitor crops and use fungicide as soon as a disease is identified.
• DPI Cereal Disease Guide 2011 sets out resistance ratings for growers to assess risk.

Victorian grain growers are being warned to watch out for disease this winter, after experiencing the wettest summer on record.

DPI senior plant pathologist Grant Hollaway said the potential for diseases in cereal crops this year was the highest in more than three decades.

"Widespread summer rains have supported volunteer cereals — the grain bridge — which will carry over rust diseases that built up during 2010," Dr Holloway said.

"Also stubble borne diseases will be at higher levels following heavy crops and the opportunity for early sowing will favour many diseases."

Dr Hollaway advised growers to review the resistance of the varieties they had planted and their management to date and implement the appropriate strategy.

Know your enemy

With the opportunity now passed to reduce disease risk through variety selection, crop rotation and chemicals, fungicides are the main option still open to growers.

Dr Hollaway said before using fungicide, farmers should also make sure they have accurately identified the disease.

"There are a number of non-disease issues in crops that could be a result of nutritional or chemical damage," he said.

Once the disease is confirmed, Dr Hollaway said fungicides should be used as soon as possible.

"We recommend active monitoring, then if fungicide is warranted it needs to be applied early in the disease development. Don't wait for the disease to take hold."

Dr Hollaway said fungicides had become more affordable and versatile in recent years, thanks to a drop in manufacturing costs and the development of new chemistries.

He said there was also a sound economic basis for managing disease early, particularly after a 2009 Grains Research and Development Corporation study supported by the DPI.

"Without current control strategies these losses could double," Dr Hollaway said.

Cereal Disease Guide

When judging the risk associated with their cereal variety, Dr Hollaway recommended using this year's Cereal Disease Guide, produced by DPI and available on its website.

The guide is based on the results of the Australian grains industry national variety trials (NVT) system, which provides independent data to growers to assist with cultivar selection.

DPI is the national co-ordinator of developing and communicating disease ratings for wheat, with Dr Hollaway its national co-ordinator of wheat disease screenings, a role facilitated with the NVT manager based at Grains Innovation Park, Horsham.

DPI distributes NVT wheat lines nationally for disease testings by Australia's leading wheat pathologists, including members of its own staff, who are responsible for screening 37,000 NVT wheat lines.

These are tested in the field for their reaction to four important diseases — yellow leaf spot, leaf rust, stem rust and stripe rust — and in a glasshouse to yellow leaf spot.

Armed with results from all over the country, DPI assigns disease ratings to wheat cultivars, which are subsequently published on the NVT website.

The ratings refer to the resistance of cereal varieties to the ten most common forms of disease.

Resistance ranges from very susceptible — where losses greater than 50 per cent are possible — through to resistant where the disease will not multiply, or cause any damage.

When all the results are collated in February, DPI compiles the grain cultivar results most relevant to Victoria into its annual guide.

Dr Hollaway said the guide was an essential guide for the state's grain farmers.

"For growers to effectively manage a range of diseases they need good information on the reaction of their cultivars to the diseases of importance in Victoria."

Used early, Dr Hollaway said this information could also help growers select cultivars that would help minimise disease in their crops.

An example of the guide's advice about wheat disease reactions is shown in Table 1.

Table 1: Wheat Disease Reactions Table

R = Resistant MR = Moderately resistant MS = Moderately susceptible S = Susceptible VS = Very susceptible
Variety	Rust			Cereal Cyst Nematode	Yellow leaf spot	Septoria tritici	Crown rot
	Stem	Stripe	Leaf	Res
Axe	MS	R-MR	MR	S	S	S-VS	S
Bolac	MR	R-MR	MS	S	MS-S	MS	S
Catalina	R-MR	MS	R-MR	R	MS-S	MS	S
Derrimut	MR	MS-S	R	R	S	MS-S	S
Estoc	MR	MR-MS	MR-MS	MR	MS-S	S
Mace	MR	S-VS	R	MR-MS	MR-MS	MR-MS	S
Scout	MR	MS	R	R	S-VS	MS	S
Wyalkatchem	MS	S	R	S	MR-MR	S
Yitpi	S	MR-MS	MS-S	MR	S-VS	MR-MS	S
Young	MR	MS	MR	R	MR-MS	MR-MS	S

The risk factors

Dr Hollaway said stripe rust was a particular threat again this year, especially after the high levels found in wheat and triticale crops across the state last year.

A common concern with stripe rust, head infection should be controlled by applying a foliar fungicide prior to ear emergence.

Dr Hollaway said a number of wheat varieties that were adult plant resistant (APR) were susceptive as young plants.

"These varieties typically need protection from stripe rust until the onset of APR."

Stem rust was also common in 2010 and is set to be a significant threat this year.

"Due to the high risk of stem rust this year, preventative fungicides sprays may be warranted in susceptible crops before symptoms appear," Dr Hollaway said.

Leaf rust was also common in susceptible cultivars across the state last year, while yellow leaf spot was particularly severe in early Mallee crops. Both should be looked out for and treated early.

Dr Hollaway recommended growers who had sown varieties that were below suggested minimum resistance levels (see Table 2), carry out additional control as a matter of course.

Table 2: Wheat - Suggested minimum levels of resistance

Production region annual rainfall (mm)	Rust			Yellow leaf spot	Septoria tritici
	Stem	Stripe	Leaf
Low < 350	MS-S	MS	MS	MS-S	S
Medium 350–500	MS	MR-MS	MS	MS-S	MS
High > 500	MR	MR	MR	MS-S	MS

Looking to 2012, Dr Hollaway recommended growers choose cultivars carefully, avoiding rust susceptibility.

He said choosing for resistance was the best weapon against disease.

"It is simple, reliable and cheap to use. The use of resistant cultivars also reduces the use of fungicides which can negatively impact on the clean and green image of Victoria agriculture."

Early in the season, growers should also consider rotating crops and make sure they remove the green-bridge by March. Fungicides on seed or fertiliser should be applied prior to sowing.