A WARNING has been issued to canola growers in the State's south to monitor for Diamondback Moths (DBM) during the growing season.
They were first recognised in areas around Boxwood Hills, Wellstead and Borden during July and August.
The moths have since spread to the Jerramungup and Jacup areas with isolated populations being recognised as far west as Gnowangerup and Broomehill.
Landmark agronomist Stuart Witham recommended that growers monitor their canola closely and consult an agronomist if needed.
"We began to recognise them in July and August and have been monitoring them throughout winter up until three weeks ago," he said.
"The warm weather and the moth's quick lifecycle means that they've been dormant over the slightly wetter winter months and re-surfaced with the dryer weather."
Affected canola plants will have the leaves targeted while the plant is green and the stem and pod will be targeted as the plant begins to dry out.
"They're suckers so rather than actually chewing the stem the moth will suck the moisture from the plant," Mr Witham said.
Stressed and drying crops are the most vulnerable to DBM although strong healthy crops aren't immune.
It's been recommended that spraying for the moth, on the ground or via aerial application, will eradicate up to 70 per cent of the moths within the crop and growers have also been advised to be aware of withholding periods.
Monitoring has also been recommended for between five and seven days after spray application.
"It's mainly the early sown crops that have been affected," Mr Witham said.
"Crops sown in April and May that were dry in the ground and remained that way for six to eight weeks up until the first lot of decent rains have allowed the moths to build up numbers at a base level.
"Those are the crops worst affected and the rains in mid-March allowed the numbers to build up on the early canola volunteers.
"They settled down when the weather broke and have re-emerged in the long period of dry since then."
Contrary to belief it has been suggested that the slow movement of pesticides from the Eastern States due to high locust numbers rather than the shortage of planes is slowing spray application in the area.
"I've been talking to farmers with affected crops and most of them have been able to get planes to spray within a week to 10 days," Mr Witham said.
Cabbage aphids have also been wreaking havoc in canola crops in the area.
"Some growers have sprayed specifically for the aphids but those whose crops are affected by the moths are spraying and eliminating both at the same time," Mr Witham said.
"The best advice I can give is buy a sweep net, get out into the paddocks and have a good look because monitoring is the key."
Elders agronomist Mitch Tuffley agreed with Mr Witham.
"I've been monitoring several farms around Borden and Jerramungup over the past couple of weeks," he said.
"In Borden I'm finding numbers up to 300 plus in every 10 sweeps and at the moment numbers in Jerramungup are lower with between 80 to 100 but are building rapidly.
"The threshold is around 80 to 100 every 10 sweeps depending on the stage of the crop.
"The warm dry weather we're experiencing provides the perfect condition and encourages a much quicker lifecycle of 10 days to two weeks.
"The economics of the decision to spray is becoming more difficult as the yield potential is decreasing every day we don't have rain.
"At the same time the warm dry weather and stressed crops provide the potential for DBM numbers and crop damage to increase.
"Successful control is very difficult due to the rapid lifecycle and two well timed sprays are generally needed especially when threshold numbers are met early in the season.
"I'm hoping we can achieve good control from a first spray followed by some rain and cool weather which will slow the DBM down.
"Then hopefully numbers will stay down and get us through to swathing without having to do a second spray but it's unlikely.
"Swathing is probably two to three weeks away in the area but it may be brought forward if this weather keeps up.
"I'm hoping the rain forecast for this Saturday or Sunday is actually going to come through and help finish off some of the crops that are suffering badly at the moment."
