Tuesday, 8 May 2012

Cotton stainers attack


A pale cotton stainer.

By BRAD PFEFFER, Australian Cotton Outlook
THEY are bright red, good at hiding, and enjoy feasting on cotton bolls.
And the cool season has given rise to large numbers of this pest - pale cotton stainers - which have been making a meal of cotton crops across most growing areas this year.
And simply, the pest has not been a problem in the past as it is typically called from heat about 40 degrees Celsius, and in pre-Bollgard days was usually a secondary casualty of heliothis control.
But the unique 2007/2008 season has seen many growers opt to chemically control the bug to mitigate potential yield losses, and even potential downgrading issues.
As the stainers eat the maturing seed, they can affect seed weight, oil content, and seed viability. Tightlock can result around damaged seeds, preventing the lint from fluffing out as the boll opens.
Dr Lewis Wilson with the CSRIO said that part of the problem came with the fact that little was known about pale cotton stainers, purely because they hadn’t been a problem in the past.
While they affect cotton crops across the world, Australia typically escapes the worst of their damage.
“But the damage can range widely to quite severe,” he said. “They have a proboscis that is very, very strong.
“Whereas green vegetable bugs or mirids target younger bolls, these guys have a strong proboscis and can target hard bolls, and even lay their eggs in open bolls.”
Damage to young bolls can cause them to shed, while damage between eight days and opening has various consequences.
“When they feed on a boll they also defecate and their faeces is a yellow sticky stuff in patches through the lint.
“We have found that this can cause downgrading.”
The Cotton CRC has set a tentative threshold of three per metre for pale cotton stainers, although Dr Wilson also warned that they could be difficult to find.
He said that they liked to hide below the canopy, and that detection with a beat sheet required patience. They can also disperse around a paddock in patches, making thresholds and counts harder than usual.
He added that because they were often in the low levels of the plant this could also make chemical control more difficult at times.
He said there were two pyretheroids registered for their control in Australia, whole others would also control them, as would some organophosphates.
“Make sure you look at your crops for this pest. You don’t need to panic over them; but you need to be aware they could be there.”

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