Australia
May 8, 2014

Blackspot of field peas risk autumn 2014 - Didymella pinodes/Phoma medicaginis var. pinodella

Grain growers and advisers in the southern cropping region are being equipped with a new resource to help them determine the risk levels of soil-borne diseases this cropping season.
The South Australian Research and Development Institute (SARDI) Soil Biology and Diagnostic team has produced an online series of maps detailing information gathered during autumn from PreDicta B soil samples across the mainland cropping regions.

SARDI science program leader Dr Alan McKay (pictured) says the maps summarising distribution and levels of each soil-borne pathogen assessed can be viewed here.


“We are excited to be able to present this data as distribution maps for all agronomists and growers to utilise on the upgraded PreDicta B website which will be developed further over the next few months,” Dr McKay said.

PreDicta B is the national DNA-based soil diagnostic service operated by SARDI, with support from the Grains Research and Development Corporation (GRDC) and SA Grain Industry Trust (SAGIT).

PreDicta B samples are processed weekly from February to mid-May – prior to crops being sown – to help growers plan cropping programs. About 600 grower PreDicta B samples have been used to generate the latest data and the new series of maps.

More than 1000 agronomists around Australia have been accredited by SARDI to interpret the results and provide advice on management options which aim to reduce the risk of yield loss due to soil-borne threats.

According to Dr McKay, PreDicta B soil test results so far in 2014 indicate take-all, rhizoctonia and crown rot are the main soil-borne disease risks this season.

“While most people will be expecting and planning for rhizoctonia and crown rot management, take-all could catch some people out,” Dr McKay said.

“Take-all inoculum levels are the highest in more than a decade and growers and advisers managing intensive cereal or cereal/pasture rotations should plan ahead to avoid yield loss later in the season.

“Take-all inoculum levels have been increasing with the run of good seasons across southern Australia. Levels in some paddocks now are high enough to cause large losses if growers sow wheat and we have a good season combined with a tight finish.”

Dr McKay said the extent to which the disease would be an issue in individual properties would depend on the crops sown and the type of season ahead. Paddocks most likely to have yield losses are those that have had a high frequency of cereals and/or grassy pastures and are going to be sown to wheat in 2014.

“If you have to go back to wheat then there are several fungicides registered for take-all suppression that will help to reduce losses in paddocks in low to medium take-all risk categories. Also control any green bridge and sow these paddocks later in the seeding program.

“In high take-all risk paddocks consider sowing a break crop or grass-free pasture. The take-all fungus is controlled by a one-year break from cereals and host grasses.”

Take-all restricts water and nutrient flow up the root system. Under periods of moisture stress, typically triggered by dry, northerly winds the roots cannot supply enough moisture so the plants die prematurely. In severe cases, yield losses can be large.

Rhizoctonia levels are higher in 2014 compared with last year, according to Dr McKay. Significant rainfall in some parts of south-eastern Australia in February will have reduced the risk of rhizoctonia but it will still be a problem, particularly in non-wetting soils.
He advises growers to sow high rhizoctonia risk paddocks going into cereals early in the seeding program.

“Soil disturbance below the seed and adequate nitrogen fertiliser placed below the seed will stimulate early root growth down the soil profile and reduce the impact of the disease. Higher sowing rates may also help compensate for the loss of tillers in high rhizoctonia paddocks, but would not be recommended if take-all levels are also high,” he said.

SARDI research scientist Marg Evans says crown rot continues as an issue for cereals, particularly durum wheat, and high levels of crown rot have been detected in soil samples across all southern states.

“Knowing soil inoculum levels and the risk of yield loss from crown rot in each paddock will be a powerful management tool for 2014 as good rains during 2013 make it difficult to predict the amount of inoculum break down under non-cereals and inoculum build-up under cereals,” Dr Evans said.

“If sowing cereal into a paddock with medium to high levels of crown rot, sow barley – which rarely exhibits yield loss – in preference to bread wheat (susceptible) and avoid sowing durum wheat (very susceptible). Avoid applying high levels of nitrogen at sowing and early in the season as this encourages bulky growth which will increase the risk of moisture stress during grain fill and may increase yield losses from crown rot.

“Crown rot infection occurs when infected residues come into contact with growing cereals, so where stubble has been knocked down by machinery or heavy grazing, stubble displacers ahead of the sowing tines/disks may be advantageous. Yield losses from crown rot may also be reduced by sowing between the rows of the previous cereal stubble.”
 

Website: http://www.grdc.com.au

Published: May 8, 2014