Dry climatic conditions can lead to symptoms that appear to be herbicide failure, according to GRDC-sponsored research in Western Australia. A report found that 1995 conditions led to a staggering increase in the amount of herbicide applied in the Central wheatbelt and Great Southern region.
"A lot of farmers were worried they were experiencing herbicide failure or resistance, but in most cases the symptoms were due to weather conditions," Agriculture WA researcher David Minkey said.
"Plants suffering fertiliser and moisture stress are harder to kill so it is important for farmers to look for stress symptoms before they spray."
Indicators of moisture stress for ryegrass include a reddening of the plant and roots that are longer than the shoots.
"The most successful herbicide application programs targeted healthy plants between one and two weeks after emergence," said Mr Minkey.
Mr Minkey said the best time to spray was when the relative humidity was 85-90 per cent and the temperature about 15 degrees Celsius.
Contact: Mr David Minkey 098 928 477