Bet each way with Rhizo protection

Image of Dr Alan McKay

SARDI’s Dr Alan McKay inspects root systems affected by Rhizoctonia.

PHOTO: Alistair Lawson

Season 2015’s dry spring will increase the risk of Rhizoctonia this season, according to South Australian Research and Development Institute (SARDI) science leader for soil biology and diagnostics, Dr Alan McKay.

The 2015 season was a bad year for Rhizoctonia due to a combination of factors that started with a dry spring in 2014, which favoured a build-up of the disease. The generally dry 2014-15 summer kept levels high and this, combined with a relatively cold start to the season, resulted in early-sown crops exhibiting bare patches.  

Possible herbicide carryover from 2014 may also have contributed to greater damage than normal by reducing early crop vigour. This reinforces the need for growers to check herbicide labels for re-crop intervals as soil moisture affects the microbial activity required for the degradation of some herbicides.

Dr McKay says some 2015 wheat sown following break crops in 2014 also got hit hard by the root disease when normally it would not have been.

“We are not completely sure why, but suspect that the break crops might not have been completely grass-free, as grasses and cereals are the main hosts of Rhizoctonia,” Dr McKay says.

“Where we have had a long, hot summer, then Rhizoctonia will be a potential problem this year, especially if the soil is relatively cold at seeding,” Dr McKay says.

Dr McKay says early indications are that where the 2015 season was particularly poor in some areas of Victoria, many growers will be planting wheat on wheat in 2016 to recover some of the inputs from the previous season. However, that strategy carries increased risk of soil-borne diseases including crown rot and Rhizoctonia.

New fungicides

With GRDC funding, SARDI and the Department of Agriculture and Food, Western Australia (DAFWA) have been evaluating new fungicides and looking at more effective ways of applying them at seeding to get better control of Rhizoctonia root rot.

Fungicide application below the seed was investigated to protect the seminal roots, which are important for early seedling vigour and extraction of deep moisture late in the season. The surface application was evaluated to protect the crown roots, which support the size and number of tillers per plant. Seed treatments provide some protection to both crown and seminal roots.

“A complicating factor was that a healthier root system did not also result in a significant yield response,” Dr McKay says. “Responses were smaller and less reliable when spring rainfall was low, so we need to investigate this further to better understand how much rainfall is needed for yield to benefit from a healthier root system.”

The fungicide efficacy trials were co-funded by Bayer and Syngenta on the understanding that they would seek label registrations for successful new methods of application, which has been done. 

The EverGo Prime field trials focused on different ways of applying the same rate of product. A combined analysis of field trials show that EverGol® Prime at 80 millilitres per 100 kilograms of seed or 80mL/hectare applied in-furrow below the seed produced significant yield increases of between 0.14 and 0.19 tonnes/ha in barley. A dual application of 40mL/100kg of seed combined with 30mL/ha in-furrow gave the best root health scores but this did not translate into a yield increase. Despite that, Dr McKay says it is still a technique worth further investigation.  

“Syngenta developed Uniform® as a liquid band or coated fertiliser treatment,” Dr McKay says. “In our trials, a dual application of Uniform® 200mL/ha on the soil surface behind the press wheel and 200mL/ha on the base of the furrow about three to four centimetres below the seed produced the most reliable and greatest yield responses of 0.32t/ha for wheat and 0.45t/ha for barley,” Dr McKay says.

“Essentially, this split application targets both primary and secondary root systems and offers a more effective strategic protection across several season-dependent scenarios.”

According to University of South Australia agricultural research engineer Dr Jack Desbiolles, also involved in the project, it is important to maintain a constant stream with accurate flow control when using liquid systems.

“A key advantage of a liquid banding system is that it enables growers to target fungicide application at the potentially high-yielding areas of the paddock at risk from Rhizoctonia, where yield response may be most profitable,” Dr Desbiolles says.

“A limitation of the split application is the increased water volume per hectare, and dedicated research is needed to validate how low a water rate can be without compromising the crop response.”

Uniform® is also registered to be applied to granular fertiliser and Dr McKay says this will be the option for the 80 to 90 per cent of growers who do not have liquid capability on their seeders.

Dr Mckay says it is important for growers to seek local advice on fertiliser rates as they need to be sufficient to ensure an even distribution of fungicide in the planting row to ensure optimum protection of the root system.

Another way for growers to reduce the yield impact of Rhizoctonia this year is to increase sowing rates, within an acceptable range for each rainfall zone. This could be worth considering where growers are sowing wheat back on failed wheat crops in paddocks where Rhizoctonia is the main soil-borne disease risk.

“Increasing seeding rate can decrease yield loss to Rhizoctonia because there are more main stems per square metre,” Dr McKay says. “When we increased the seeding rate from 70kg/ha to 94kg/ha we got an 18 per cent yield increase. The roots were still damaged but there were more heads per square metre.”

More information:

Dr Alan McKay, SARDI,
08 8303 9375,

alan.mckay@sa.gov.au;

Dr Jack Desbiolles, University of SA,
08 8302 3946,
jacky.desbiolles@unisa.edu.au

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HRZ disease adapting to drier climes

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GRDC Project Code DAS00122, DAS00123, DAS00125

Region South, West