Farm Management

Growers get the jump on costly soil-borne diseases

Alan McKay

Growers across the Grains Research and Development Corporation (GRDC) southern cropping region are avoiding extensive yield and economic losses by knowing the risk of soil-borne diseases before they begin sowing 2017’s crops.

Many growers in South Australia, Victoria and Tasmania have already had their soils tested to determine the levels of disease-causing pathogens present through the PREDICTA B DNA-based soil testing service provided by the South Australian Research and Development Institute (SARDI)  and supported by the GRDC.

Results of those tests indicate that take-all is at slightly higher levels than 2016, with around 21 percent of samples tested showing a medium to high disease risk, according to SARDI principal scientist Dr Alan McKay.

“The risk of crown rot in the southern region has declined, with 22% of 2017 samples so far in the medium to high disease risk category, compared with almost double that in 2016” Dr McKay says. “That is most likely due to greater breakdown of inoculum in break crops.”

The risk of yield loss caused by rhizoctonia, root lesion nematode, and cereal cyst nematode is similar to 2016 at 27%, 5%, and 1% of samples tested respectively. Medium to high levels of eyespot have been detected in 15% of samples from SA.

On average, Australian grain growers each year incur more than $200 million in lost production due to cereal root diseases such as take-all, rhizoctonia root rot, crown rot, root lesion nematode, cereal cyst nematode, stem nematode, and blackspot of peas, which can cause significant yield losses by limiting water and nutrient uptake.

Diseases can also lead to reduced crop competition for weeds, increased crop damage from some herbicides, and a reduction in cropping options.

“But if growers know which soil-borne pathogens are in their soils prior to seeding, they can take evasive action and avoid potentially serious crop losses,” Dr McKay says.

By using PREDICTA B, a unique DNA testing service for soil-borne pathogens, and combined with advice from an accredited agronomist, growers can implement management strategies before losses occur.

Dr McKay says results are typically used to guide management decisions at the beginning of the cropping season as very little can be done once the crop is sown.

“Results from tests also enable growers to monitor the effect of changed farming practices and seasons on disease risk and allow them to make better informed variety, rotation, and paddock management decisions,” he says.

Potential high-risk paddocks include those with bare patches, uneven growth, and whiteheads in the previous crop; paddocks with unexplained poor yield from 2016; newly purchased or leased land; cereals on cereals or following grassy pastures; durum crops (crown rot); and paddocks coming out of chickpeas (root lesion nematodes).

Growers wanting to determine the risk of disease in their paddocks can access PREDICTA B diagnostic testing services through a SARDI-accredited agronomist. The agronomist will interpret the results and provide advice on management options to reduce the risk of yield loss.

About 1800 agronomists and consultants across Australia have been PREDICTA B accredited through SARDI’s annual Agronomist Root Disease Risk Management training courses, supported by the GRDC.

SARDI processes PREDICTA B samples weekly from February to June, and less frequently at other times of the year.

PREDICTA B  tests for most of the soil-borne diseases of cereals and some pulse crops, including crown rot (cereals); rhizoctonia root rot; take-all, including the oat strain; Pratylenchus thornei; Pratylenchus neglectus; cereal cyst nematode; stem nematode; and blackspot in field peas.

The testing service also focuses on demand for identifying new diseases, and new tests are regularly added to the portfolio of issues that can be identified. New tests currently reported as tests under evaluation (risk categories still being determined) are ranked within a population density in the interim, and include eyespot, Pratylenchus quasitereoides and Pratylenchus penetrans.

The testing service is being adapted to the different geographical regions throughout Australia’s grain-growing areas.

The use of PREDICTA B as a diagnostic tool has increased over recent years with recent development of capability to test for both soil-borne and foliar pathogens.

The GRDC is exploring ways to encourage further use of the test to improve broadacre crop performance and minimise economic losses.

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