Growers are being reminded that some herbicides are residual in the soil and future paddock sequences need to be planned ahead to avoid damage to crops and pastures.
Research undertaken at a Department of Agriculture and Food, Western Australia (DAFWA) trial site at Brookton has shown the damage done to lupins, peas and a range of pasture legumes where the herbicide Clopyralid and others were sprayed the previous year on a wheat crop.
DAFWA researcher Ron Yates said the study aimed to better understand the effect of residual herbicides on legume growth particularly focussing on nodulation and nitrogen fixation.
“Legumes are a valuable component in the farming system as they reduce nitrogen fertiliser costs however some legumes may not be producing much nitrogen as a consequence of herbicide effects,” Dr Yates said.
Funded by DAFWA and Grains Research and Development Corporation (GRDC) through the Focus Paddocks project, researchers have found that a significant level of damage was occurring in susceptible crops.
“For example Clopyralid when used at the rate of 125 grams per hectare has a recommended plant back or interval period on the label of twelve months,” Dr Yates said.
“So even with 70 millimetres of rain falling over January to March this past growing season, there was still residue in the soil at planting time.”
The herbicides were sprayed on the 17 July 2012 and the legumes were sown the following year on the 27 May 2013.
The trial was shown to 50 growers and agribusiness representatives at a Field Day on the 26 September at the property of Colin and Anna Butcher.
Dr Yates says that growers need to plan their sequences so the adverse affects of herbicide carryover are prevented.
“In this case, a cereal or canola crop would be the most appropriate choice to allow the necessary time for herbicide breakdown”.
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