Crop Doctor
The Grains Research & Development Corporation

Ergot remained a problem for sorghum growers towards the end of last season but research shows management can minimise the impact of the fungus and its associated "honeydew".

According to Queensland Department of Primary Industries and Fisheries pathologist Malcolm Ryley, early planting ­ before mid-January ­ and strategic harvesting of infected patches of crop are probably the most significant practices to reduce ergot impact.

Dr Ryley told a Grains Research Update for Growers at Millmerran the goal of the sorghum ergot management strategy was to minimise the chances of infection and to reduce the sclerote levels in infected crops to below the stockfeed limits.

Currently these were  0.3% by weight for all livestock but, from April 1, 2004, the limit for feedlot cattle would be  0.1%.

"Ergot outbreaks are driven by weather, with infection worse when a crop flowers in cool, wet weather," Dr Ryley said.

"Airborne spores of ergot land on the stigmas of sorghum flowers and the fungus grows into the ovary. Toxic sclerotes ­ which are the major concern with ergot ­ develop in place of the seed. However well pollinated crops have little or no ergot.

"While sclerotes do not survive in soil from one season to the next, and so don¹t contribute to the following season¹s outbreak, the fungus can survive year round on living plants of sorghum weed species like Sorghum almum and Johnson Grass.

"Their control can reduce local levels of ergot but not necessarily ensure a crop will not get the disease because spores can blow in from many kilometres away ­ certainly from hundreds of kilometres and possibly thousands.

"That means sorghum can be planted again into a paddock in which the previous crop was infected."

Dr Ryley told the Millmerran Update that, while planting sorghum after mid-January increased the risk of ergot, planting before then might not ensure freedom from the disease, because dry conditions during the season could lead to late germination, and later flowering, of some plants in the crop.

Growers should aim to plant on good soil moisture, on even country, to maximise even flowering

Harvesting strategies should take account of ergot levels being higher at the edge of many sorghum crops, reflecting the direction from which the spores came, and infection usually being worse in later flowering parts of a paddock, or where the plant population was poor.

"We advise harvesting badly infected areas of crop separately and point out that, according to our trials, increasing header fan speed can reduce ergot levels significantly," Dr Ryley said.

"With the level of toxic alkaloids in sclerotes the critical issue, the ultimate pre-marketing test is a determination of alkaloid levels, currently only available from the Animal Research Institute, at Yerongpilly in Brisbane. 

"Another option is to mix clean and contaminated grain to reduce sclerote levels to the accepted livestock standards."

The Crop Doctor, Peter Reading, is the managing director of the Grains Research and Development Corporation (GRDC).