Department entomologist Kevin Walden said Diamondback moths have been found in canola crops in the northern agricultural region.

He said yield loss due to plant stress caused by DBM eating canola leaves and stems can be as high as 80 percent.

“If DBM infests canola early in the season and there is enough warmth to complete three or four generations, numbers can quickly build, exceeding threshold levels,” he said.

“If they can’t be found in early August, the risk of economic damage for the rest of the season is small.

“The key to control is to constantly monitor populations from now on.

“Growers are strongly advised to sample moth numbers using 10 sweeps, with a sweep net at four or five different locations within the crop.

“If they are found, there is potential for numbers to increase and growers must resample and contact their local agronomist for advice.”

Mr Walden said a recent Grains Research and Development Corporation supported study offered new information on moth control.

“We discovered that spraying to control the moth should begin at the end of August, rather than waiting until late September, which had been accepted practice,” he said.

“In high risk situations a second spray should be applied within seven days of the first.”

More information is available from DAFWA’s PestFax newsletter, which advises on outbreaks and recommended treatment and can be viewed at www.agric.wa.gov.au