Grapegrowers can now be detectives and pinpoint the likely herbicide causing damage to their crops, new research suggests.
Herbicide drift is a major problem for grapegrowers but until now, it has been difficult for growers to recognise the source and type of grapevine damage.
However, a recently completed research project has shed new light on the understanding and management of herbicide damage.
Upward leaf rolling with yellow and brown interveinal lesions? Most likely dicamba exposure.
Severely deformed lateral shoot leaves? Most likely 2,4-dichlorophenoxyacetic (2,4-D) acid exposure.
Delayed injury? Glyphosate is your likely culprit.
Principal Investigator Dr Gerhard Rossouw was with the National Wine and Grape Industry Centre (NWGIC) at Charles Sturt University during this Incubator Initiative study to investigate a question posed by the Greater NSW Regional Program cluster.
He applied simulated herbicide drift – including 2,4-D, dicamba, MCPA and glyphosate – on potted Tempranillo grapevines after they ceased flowering. The vines were then tracked for visual shoot, leaf and fruit symptoms of damage until fruit maturity.
Dr Rossouw said his study found that while the four herbicides induced similar visual symptoms, there were some unique features that could allow their differentiation.
‘For example, dicamba exposure exhibited upward leaf rolling in conjunction with yellow and brown interveinal lesion development. Unlike MCPA, 2,4-D damage did not exhibit leaf margin necrosis, whereas severely deformed lateral shoot leaves developed only after 2,4-D exposure’, he said.
‘In contrast, glyphosate related injuries emerged later than those induced by other herbicides.’
Dr Rossouw and his team found that photosynthesis of newly emerged mature leaves was impaired by prior 2,4-D, MCPA and glyphosate exposure; and fruit yield was significantly reduced by 2,4-D, mainly as a result of bunch necrosis.
‘The herbicide also increased juice titratable acidity but most of the other basic compositional parameters were not affected’, Dr Rossouw explained.
Interestingly, while root structural development was limited by 2,4-D, dicamba and MCPA, none of the herbicides altered root carbohydrate reserve levels.
However, primary bud necrosis was pronounced – especially following 2,4-D and dicamba exposure.
‘This finding suggests that 2,4-D presents a significant hazard not only on the yield of the current season, but also for the next.’
Dr Rossouw said while the visual description of responses to 2,4-D, dicamba, MCPA or glyphosate could play a valuable role in assisting grapegrowers to assess herbicide injuries – and subsequently better manage the damage and identify the drift source – it was not the all-in answer.
‘It remains clear that visual-only assessments can still cause confusion, as many symptoms are not herbicide specific.’
However, he said overall, the study provides novel results that will benefit the wine sector in terms of understanding how grapevines respond to herbicide damage – and the short – and longer-term implications of herbicide damage.
Dr Rossouw said he was keen to conduct future work comparing drift rates and herbicide exposure at different growth stages.
‘I’d also like to assess additional herbicides such as diuron and oryzalin; and look at the repercussions of two or more herbicide combinations. This is important, because it is an increasingly common practice to use herbicide combinations to combat problematic weeds in agricultural areas.’
The project's final report is available here.