‘Stay vigilant’ is the message being sounded to wheat growers across New South Wales and Queensland looking to minimise the threat of crown rot infection.
It’s no casual reminder—crown rot is one of the most serious disease threats to winter cereal crops in Australia and growers are being encouraged to weigh up their crown rot risk when planning 2017’s winter cropping program.
Results from PREDICTA® B DNA-based soil tests across northern New South Wales and southern Queensland so far in 2017 suggest that crown rot and Pratylenchus thornei risk for 2017 crops are similar to 2016, with 26% and 49% of paddocks recording medium to high risk levels respectively.
Caused by the fungus Fusarium pseudograminearum, crown rot is widespread in wheat, barley, and durum paddocks in central and northern NSW and southern Queensland and can have a serious impact on yields.
Over the years trials have shown that with high infection, yield losses can be more than 50% but importantly, even at low inoculum levels, you can still get yield losses of 25% if the season is favourable.
The Grains Research and Development Corporation (GRDC) is committed to helping growers recognise and manage the crown rot risk and has released a series of simple videos which detail pathogen behaviour, disease symptoms, where and when to assess crops, how to identify the disease, and management options.
The videos feature interviews with NSW Department of Primary Industries senior plant pathologist Steven Simpfendorfer who is renowned as one of Australia’s leading experts in crown rot research.
Dr Simpfendorfer encouraged growers to assess the inoculum levels of individual paddocks so long term management plans could be enacted to reduce the risk of crown rot infection and crop yield loss.
“There’s nothing you can do in-crop to limit crown rot infection, most of the management decisions are upfront in terms of crop and variety selection and stubble management,” he said.
“But in terms of assessing inoculum levels, growers can look from late tillering onwards to see if there’s browning of the outer leaf sheath. This will become very apparent from flowering to grain fill if the crop is under moisture stress.
“Immediately post-harvest is a good time to visually assess the crop—if you can see the basal browning on the stubble residue then that’s a heads up on what your inoculum levels are for the coming few years.”
Crown rot is a stubble-borne disease and for a plant to become infected it must come into contact with inoculum from previous winter cereal crops.
It infects through the base of the plant and restricts the movement of water up the stem throughout the season.
While basal browning is very characteristic of crown rot, as the season progresses the expression of the disease is impacted by moisture and temperature stress during grain fill and often results in the appearance of whiteheads.
Soil and plant water potential, soil nitrogen, and inoculum loading all influence the extent of crown rot infestation and yield loss can occur even without the formation of whiteheads. Whitehead formation is most severe in seasons with a wet start and dry finish.
“Once you identify a crown rot issue, it’s important to accurately assess inoculum levels and determine whether you are in low, medium, or high risk with the stubble load.
“That’s when you need to consult your agronomist to put long term management plans in place using crop rotation and variety selection.”
The PREDICTA® B testing service is offered through the South Australian Research and Development Institute (SARDI) and provides an indicator of root lesion nematode populations and crown rot risk which is useful prior to planting to establish the level of disease risk crops are exposed to and if alternative crop types or varieties should be grown.
However it is important to remember that using the correct sampling technique is critical to its accuracy. It isn’t a simple add-on to a soil nutrition test.