Source: The Crop Doctor, GRDC

We know from the cop shows on television that the early, obvious “suspect” generally isn’t  “the one who done it”.

That appears to be so in the case of  “unidentified sunflower disorder” up in Central Queensland, where the serious money was on herbicides – residual or drift – fitting the bill as the likely cause. 

The disorder came onto the scene in 2004 – and returned again in 2005 – to slash sunflower yields in Central Queensland and, in some cases, cause total crop failure.

Naturally enough sunflowers rapidly lost their attractiveness to growers in what used to be Australia’s biggest production area.

Results of a QDPI&F grower survey and observations by field personnel estimated the extent of the disorder in the 2004 CQ sunflower crop was about 80 per cent of paddocks infected.

On average 30 per cent of plants in affected paddocks displayed the disorder, which caused an average of 90 per cent yield loss in affected plants. 

Working on the basis of a “normal” CQ season of 60,000 tonnes of sunflowers, at $350 a tonne, QDPI&F estimate the potential production loss at 12,960 tonnes, worth $4.5 million.

Residual or drifting herbicides, nutrient deficiencies – possibly boron –an unknown pathogen, adverse environmental conditions or any combination of the above were all under suspicion.

Preliminary attempts by QDPI&F plant pathologists Gary Kong and Joe Kochman, Charles Darwin University’s Karen Gibb, and specialist weeds researcher Vikki Osten to identify the cause of the disorder were inconclusive.

Dr Kong and Dr Kochman collected samples from affected sunflower plants and looked unsuccessfully for viral, bacterial or fungal pathogens that might cause the unidentified disorder, and Dr Gibb similarly failed to identify any phytoplasmas.  

Ms Osten conducted preliminary application trials with herbicides commonly used in Central Queensland but the symptoms she produced were not consistent with those observed in the field.  

Early this year Emerald based QDPI&F senior field technician John Ladewig took up the challenge of an 18 months GRDC project to “determine the cause, impact and potential control measures” for the unidentified disorder.

John will build on the research work already done and, with more than 30 years experience in Central Queensland, he should have a good chance of bringing the culprit to book.