Why do cereal crops planted early into warm and moist soil appear healthy at the start of the season and then begin to show uneven growth from mid-winter to spring?

This season, many cereal growers across the western region are reporting uneven patches, bare areas, slow growth and stunted plants, yet nothing is obvious when examining plant leaves and stems. But the answer to their crop’s lack of performance may require a deeper look.

South Australian Research and Development Institute (SARDI) principal scientist in soil biology and molecular diagnostics Alan McKay says uneven crop growth can be caused by a number of factors including drought, soil structure or toxicity issues, nutrient deficiencies or soil-borne disease.

Dr McKay says mid to late winter is an ideal time to examine crop roots to assess the presence and the impact of soil-borne diseases.

“Several years of dry spring and summer conditions can be conducive to the build-up of fungal diseases such as Rhizoctonia root rot, which can cause yield losses of 10-50 per cent in cereals,” he said.

“This disease is particularly problematic in cases where growers have planted cereal on cereals, but where high inoculum levels are present this disease may even impact pulse and canola crops.”

In a new GRDC podcast – Rhizoctonia in 2020 – Dr McKay and fellow scientist Blake Gontar discuss the disease, which is a significant issue for lower-rainfall zones and lighter soils in Australia’s western and southern grain regions.

“We expected Rhizoctonia root rot to be an issue this year, given the seasonal conditions we’ve experienced in recent years, and particularly in paddocks where cereals were grown after cereals,” Dr McKay said.

“Sowing crops early allows the seminal root system (roots from the seed) to establish and while most Rhizoctonia seed treatments provide reasonable protection of the seminal roots, they offer limited protection to the secondary roots which develop later from the crown.

“So, while the crop may get off to a good start, if these crown roots are impacted by disease, plants are limited in their ability to forage for nutrients and moisture which manifests as stunted and uneven growth across the paddock.”

While there are limited actions growers can take mid-season to control Rhizoctonia, he says, accurately identifying the presence of soil-borne diseases is critical to inform decision-making that can reduce the impact and financial losses in subsequent seasons.

Industry concern about diseases such as Rhizoctonia is one of the driving reasons behind a new GRDC investment designed to help growers learn more about soil-borne pathogens and their management.

GRDC crop protection manager, west, Georgia Megirian, who manages the national project, says accurate identification of soil-borne disease is important for informed and effective management on-farm.

“Examining plant roots or getting a PREDICTA® B test are good options for growers to confirm the presence of Rhizoctonia or other root diseases in paddocks with poor vigour, bare patches or variations in crop growth,” she said.

“Not all above-ground crop symptoms are caused by Rhizoctonia, and not all are caused by disease. If growers are unsure, it’s a good time to carefully dig up some plants to check for common symptoms on the root systems.

"Knowing exactly what you’re dealing with will help you make the best decisions and implement management tactics that reduce the impact of diseases like Rhizoctonia going forward.”

The national GRDC project is led by New South Wales grower group FarmLink Research, in partnership with grower groups in Victoria, South Australia and Western Australia. It will extend information to growers and their advisers about topics such as typical symptoms of cereal root diseases, identification and possible management strategies.

Many workshops planned as part of this project have been deferred until 2021 due to COVID-19 restrictions, however, some digital content is likely to be developed for growers and advisers.

Demonstration sites will also be established next season to ground-truth management practices that counter pathogen infection and disease development, as well as measure disease impact on crop yield and profit.

More information: Rhizoctonia in 2020 podcast and Rhizoctonia factsheet.