Vince Payne with some of the young willow die-back from giant willow aphids among the protective planting on the banks of the Raparapawai Stream, on his Top Grass Rd property. Photo / Christine McKay
Vince Payne with some of the young willow die-back from giant willow aphids among the protective planting on the banks of the Raparapawai Stream, on his Top Grass Rd property. Photo / Christine McKay
With much of the river protection work in our district reliant on willows, the arrival of the giant willow aphid could be an environmental disaster.
"When we were out duck shooting it was raining giant willow aphid excretea," Top Grass Rd dairy farmer Vince Payne said. "We had parked our truck under the willows at Ngapaeruru for two days and it was absolutely showered in sugary water, the honey dew of the aphids."
Mr Payne said with a large amount of environmental work in this district carried out with willows, he has concerns.
"I've nine hectares of my 88ha in riparian plantings using willows, the first of which were planted in the 1970s.
The black dots are the young giant willow aphids on saplings.
"The willows have done a great job in taming the shingle and the alluvial processes, with natives regenerating underneath. Willows are a great nursery species, but in the last year I've seen them dying."
First discovered in Auckland in December 2013, the giant willow aphid has spread rapidly and John Barrow, Tararua's representative on Horizons Regional Council, has told the Dannevirke News there have been trees lost in our district.
"We've an awful lot of willows holding our rivers in place and there appears to be some trees which have died, whether they've been weakened by other causes and just finished off by the aphid, or whether it's simply willow aphid damage, it's unclear.
"It is a concern and if it becomes trouble we'll be trying to breed changed varieties."
Looking along with banks of the Raparapawai Stream on Mr Payne's farm, the black mould on some sections of the willows is the tell-tale sign the giant willow aphid has been at work, while a gap where a willow has died also indicates the aphid has had a hand in the loss of the trees. Walking in among the plantings, the ground beneath some willows is black, despite recent heavy rain, another sign the aphid is around.
"I only noticed the die-back last year when we were carrying out our willow working bee," he said. "There were large colonies of the aphid and while the willows are dormant at the moment and the colonies not so big, they are still here."
And while cutting the willow poles, used for river protection, people were left with blood-red hands from the aphids.
An adult giant willow aphid on Vince Payne's Dannevirke dairy farm.
"After cutting 1500 poles we certainly had blood on our hands," Mr Payne said. "The riparian planting of streams with willows has been one of Horizons' absolute success stories and I'd hate to see them destroyed."
While hoping native birds will feed on the aphids, Mr Payne is also looking to willow species which are resistant.
"The Salix matsudana willow, one of our most prominent willows, is where we could see the most deaths. There are willow species which so far continue to be resistant, but we all need to keep looking closer at our plantings."
Mr Barrow said a secondary problem is that the willow aphid's honey dew attracts wasps.
"This is a very, very new pest and we're not sure of all the consequences," he said.
