Keeping the lid on cereal root disease impact

Monitoring conducted through the Grains Research and Development Corporation’s (GRDC) National Paddock Survey (NPS) in recent years has revealed widespread moderate levels of root disease in cereal crops across Australia.

While root disease ratings varied between seasons and districts, results generally showed that average yield losses from soil-borne diseases in the northern region could exceed 20 percent annually if not managed effectively.

Importantly for New South Wales and Queensland growers, the research also found the presence of multiple diseases in single paddocks with at least two diseases present in the majority of fields surveyed in 2015 and 2016.

The impact of the diseases was affected by growing conditions - the 2015 growing season across the north was generally characterised by little rainfall in spring and hot grain-fill temperatures while for many, the 2016 season bought above average rainfall and minimal moisture stress during grain-fill.

Speaking at the GRDC Grains Research Update at Goondiwindi last month, NSW Department of Primary Industries Senior Research Scientist Steven Simpfendorfer said there was growing evidence that soil-borne diseases exacerbated yield impact when occurring in combination.

“In a field trial conducted by the Northern Grower Alliance (NGA) near Macalister in 2015, yield loss across six wheat varieties was greater when crown rot and the root lesion nematode Pratylenchus thornei occurred together,” Dr Simpfendorfer said.

“Similarly, yield loss associated with crown rot (Fusarium) and common root rot (Bipolaris) infection increased when both pathogens occurred together with crown rot being the primary driver of losses in lower rainfall conditions in 2015.

“Yield loss was lower in the wetter 2016 season with common root rot appearing to be a slightly higher driver of losses compared to crown rot.”

Pathogens likely to pose the greatest risk to northern cereal crops in 2018 include crown rot, root lesion nematodes and common root rot.

The DNA-based soil test PREDICTA B is an important ally for growers in the management of soil-borne diseases, particularly in the lead up to the winter season, by enabling them to assess disease risk on an individual paddock basis.

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

For results to be accurate though, PREDICTA B requires a dedicated sampling strategy and is not a simple add on to a soil test.

Dr Simpfendorfer said studies undertaken in collaboration with National Variety Trial (NVT) and NPS investments by GRDC showed that avoiding stubble when collecting PREDICTA B samples led to a significant under estimation, or failure to warn of the crown rot risk.

“This can be improved by adding two 5cm pieces of stubble from the base of the previous winter cereal or grass weed plants (one to several years old) from the 15 different locations where PREDICTA B soil cores are collected,” Dr Simpfendorfer said.

“Adding stubble in this way also facilitates testing for other stubble‐borne pathogens, such as yellow leaf spot in wheat.”

At the same time, growers are being urged to monitor the presence and populations of root lesion nematodes in paddocks to minimise the compounding effect of multiple disease interactions.

A key part of the monitoring process is determining which root lesion nematode species are present given that different species have different host ranges including differential effects on varieties.

“A national survey of root lesion nematodes confirmed that the PREDICTA B tests for P. neglectus, P. thornei, P. quasitereoides and P. penetrans are reliable,” Dr Simpfendorfer said.

“Therefore PREDICTA B can be used with confidence to determine which of the main nematode species are present in a paddock, plus the level of each species, before crops are sown.

“The research confirmed that as a general rule, P. thornei is the main species on the higher clay content black/grey soils in the north while P. neglectus tends to be the dominant species around central NSW and further south on lower clay content red/brown soils.”

Crown Analytical Services (CAS) is the service co-ordinator for the northern region PREDICTA B test and can provide northern growers and advisors with bags, soil corers, protocols and procedures for sampling as well as an interpretation of results once tests are completed.