Farm Management

Know before you sow in 2021

Steven Simpfendorfer
Steven Simpfendorfer

`Know before you sow’ needs to be a common mantra among New South Wales cereal growers this year if they are to avert costly losses from diseases such as Fusarium crown rot.

Cereal diseases were prevalent in 2020 following favourable seasonal conditions during winter and spring which, when combined with increased cereal stubble loads across much of the region, could lead to elevated pathogen levels in paddocks this year.

NSW Department of Primary Industries (DPI) data shows the major cereal diseases impacting crops in 2020 were wheat stripe rust, with widespread distribution of the newer Yr198 pathotype, spot form net blotch in barley, scald in barley and Fusarium crown rot in different winter cereal crops.

Cereal disease management was a key discussion topic at recent Grains Research and Development Corporation (GRDC) Grains Research Updates with plant pathologists urging growers to assess the range of pathogen inoculum levels within individual paddocks to help guide crop and varietal selection.

NSW DPI senior plant pathologist Steven Simpfendorfer said growers could minimise the yield impact of cereal diseases by managing three key factors – the host, the pathogen and the environment.

“Disease levels in 2021 will still be based around the disease triangle, which requires a combination of pathogen inoculum, susceptible host and environmental conditions conducive to disease development,” Dr Simpfendorfer said.

For more information on the disease triangle go to the GRDC Wheat GrowNotes.

“Cereal disease risk is likely to be higher due to pathogen build-up in 2020 and the likely increased area of cereal-on-cereal in 2021.

“All three components of the disease triangle should be considered when developing management strategies, which will help to minimise losses and determine if fungicide application is warranted.

“NSW DPI is available to assist advisers and growers in obtaining correct diagnosis and developing management options prior to sowing and as required throughout the season.”

The GRDC is encouraging growers to undertake a quantitative assessment of cereal disease risk in the lead up to the 2021 winter cropping season by undertaking PREDICTA® B DNA-based soil tests to gauge the risk of both soil-borne and foliar diseases.

This provides a valuable guide to paddock selection, crop and variety choice and required agronomic management.

Additionally, NSW DPI, with co-investment from GDRC, is offering a complimentary cereal stubble testing service prior to sowing in 2021 (January-April) aimed primarily at determining Fusarium crown rot risk levels in cereal-on-cereal situations. This can be arranged by contacting Dr Simpfendorfer on steven.simpfendorfer@dpi.nsw.gov.au.

“To manage disease risk effectively, growers need to know what they’re dealing with prior to sowing – the nature and incidence of inoculum and whether the pathogens are dispersed by wind which will dictate whether rotating to a non-host pulse or oilseed crop will break the disease triangle,” Dr Simpfendorfer said.

While break crops are the most effective tool to mitigate the risk of cereal diseases such as Fusarium crown rot, it is likely that some growers will sow back-to-back cereal crops this year.

Dr Simpfendorfer said it was critical that any growers adhering to a cereal-on-cereal rotation use the latest varietal resistance ratings and prioritise high resistance ratings for the pathogen most prevalent in the region and/or likely to cause the greatest yield loss if they have a situation where multiple pathogens are present.

He said it was also important to recognise that barley, bread wheat, durum, oats and triticale are not break crops for each other due to the fact they all host Fusarium crown rot, take-all and Rhizoctonia.

At the same time, with high stubble loads in paddocks across NSW, stubble management will play a key role in containing soil and stubble-borne diseases such as Fusarium crown rot.

“For example, inter-row sowing between intact standing cereal stubble reduces the level of Fusarium crown rot infection,” Dr Simpfendorfer said.

“However, cultivating or mulching infected cereal stubble prior to sowing can spread Fusarium inoculum more evenly across a paddock and potentially into the surface layers of the soil where plant infection primarily occurs.”

When it comes to environmental conditions, disease management options are more limited however growers should keep in mind that subtle microclimate differences within cereal canopies can have a large influence on the development of foliar diseases. Hence, canopy management can play a significant role in managing leaf diseases.

“Recent weather conditions, including in the fortnight prior, and predicted weather conditions over the ensuing two to four weeks should also be considered with in-crop leaf disease management decisions in susceptible varieties around key growth stages for fungicide application of GS30-32 (first node), GS39 (flag leaf emergence) and GS61 (flowering),” Dr Simpfendorfer said.

Conversely, yield loss from Fusarium crown rot infection, which may be expressed as whiteheads, is strongly related to moisture and temperature stress during grain filling.

Although growers cannot control rainfall during this period, Dr Simpfendorfer said there was the potential to limit the probability of stress.

“This can be done through earlier sowing (matched to varietal maturity and frost risk), maximising soil water storage during fallow periods (stubble cover plus weed control), addressing other biotic (such as nematodes, Rhizoctonia) or abiotic (including acidity, nutrition, residual herbicides) constraints to root development and canopy management,” he said.

Source: GRDC

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