Australia
January 24, 2012
Are S and VS varieties really the best option?
Column by Grant Hollaway
Chairman, Australian Cereal Rust Control Program Consultative Committee
When considering options for their 2012 cropping program, grain growers should select varieties with sufficient rust resistance to suit their own risk situation.
This means choosing varieties with the highest level of rust resistance possible, but obviously taking into account the variety’s other agronomic and disease resistance traits.
Doing your homework is essential – find out if there is an alternative to susceptible and very susceptible varieties that will suit your region. It is too late when a rust outbreak has crippled your crop yields.
While it is generally agreed that S and VS varieties are best avoided, if they are selected, a rust management plan is a must.
Growers must consider all characteristics of wheat varieties – including rust resistance – to ensure they take the guess work out of selection and make the best choice for their cropping program.
An effective rust management plan using fungicides applied to seed or fertiliser at sowing combined with subsequent foliar fungicides if required can provide effective rust management. Using fungicides to keep rust levels low will also reduce the chances of the rust changing and overcoming effective resistance genes.
However, growers should be aware that all chemicals have maximum residue limits (MRLs) that restrict the amount of active ingredient that can be applied to a single crop.
There are three rust diseases of wheat in Australia - stripe, stem and leaf. Cultivars resistant to one may be susceptible to another.
The response to rust that occurs in the field will depend on many factors, including the amount of inoculum that survives the non-cropping phase, the timing of the rust outbreak in the crop, and the pathotypes (strains) of rust occurring in a region.
By selecting varieties with appropriate levels of resistance it is possible to:
* Reduce the build-up of rust populations that cause regional epidemics.
* Decrease pressure from existing rust strains.
* Lower the chance of current strains mutating into more virulent ones.
* Reduce production costs associated with chemical use.
* Reduce the risk of significant yield and quality loss from rust outbreaks.
Rust management is like vaccination – its success relies on ‘herd immunity’. To deliver an effective rust management strategy, growers must communicate with their neighbours.
It only takes one S and VS crop with no control in a district for a rust outbreak to occur.
Growers are encouraged to pick up the phone and ring their neighbours to let them know of any rust outbreaks so they can put their management plan in place – it’s that simple.
Also, growing S and VS varieties increases inoculum levels and therefore the pressure placed on other less susceptible varieties being used in the region.
To assist with variety selection for 2012, growers should consult a current cereal disease guide. These guides provide ratings for all the common wheat cultivars growing in each state. These guides are available at www.rustbust.com.au
Initially when selecting varieties for 2012, growers should endeavour, where possible, to avoid growing varieties that are susceptible (S) or very susceptible (VS) to any of the three rusts. If this is not possible, then a suitable fungicide plan will need to be put in place. In many regions, fungicides will also be part of the management plan for partially resistant varieties such as those that are moderately resistant-moderately susceptible (MR-MS) or moderately susceptible (MS) to any of the rusts.
While the first step in rust management is variety selection, a close second is having plan in place at the start of the season to manage an outbreak. More on this next week …
For more information on variety selection visit www.rustbust.com.au
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