Disease risk in 2014
PreDicta B soil tests so far in 2014 indicate take-all, rhizoctonia and crown rot are the main soil borne disease risks this season while Pratylenchus levels are on the rise.
SARDI’s Dr Alan McKay says take-all is the disease likely to catch growers out. 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.
The extent to which the disease will be an issue on individual properties will 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,” he said.
“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. In low to medium rainfall districts (less than 450mm) grasses must be controlled by late June and by end of July in high rainfall districts.
“If the paddock must be sown to a cereal, then consider barley because any yield losses will be only half that of wheat’s potential losses, but inoculum levels will continue to increase.”
The other key contributing factor to yield loss will be a tight finish to the season with hot, northerly winds at flowering usually the key trigger for development of hay-die symptoms.
“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 to die prematurely. In severe cases, yield losses can be large,” he said.
“If there is a soft finish to the season, yield losses will not be as great, but the fungus will keep developing until the crop matures, thus posing an even greater risk to subsequent cereals.”
Dr McKay says take-all inoculum levels have been slowly 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,” he said.
“Take-all doesn’t do well in drought conditions and generally takes two to four good seasons and intensive cereals or grassy pastures for inoculum to reach high risk levels. While most people are focused on rhizoctonia and crown rot and are planning for that, take-all could catch some people out.”
Rhizoctonia levels are higher in 2014 compared to last year. Some parts of south-eastern Australia received 25-130 millimetres in February and Dr McKay says this will have reduced the risk of rhizoctonia but it will still be a problem, particularly in non-wetting soils.
“Rhizoctonia is displaced by other biota in moist soil combined with high temperatures during December to early March. Much of the rain this year fell as a single event so the soil surface would have dried out fairy quickly. So while the rain would have had a benefit, it will not be as large as growers might have anticipated. The stored moisture however will be very useful if the plant root systems are healthy enough to access it throughout the season.”
Take-all risk autumn 2014
More information: www.sardi.sa.gov.au/diagnostic_services/predicta_b
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