Potato crisps exhibiting zebra chip disease that caramelises during the cooking process. Photo: Commons: US Department of Agriculture
Researchers are finding success in tackling zebra chips- often mistaken for burnt or bitter potato chips - by bringing in "natural enemies" to fight off the bug in Canterbury.
The bug, which causes dark-coloured radial rings - like a zebra's coating - wiped out nearly 6 percent of Canterbury's potato crop three years ago.
To prevent this happening again, researchers at Lincoln University have been looking at ways to target the tomato potato psyllid - the leaf-eating insect which spreads a bacterial disease to crops.
Associate professor of horticulture Clive Kaiser said the number of affected crops had been increasing exponentially up until three years ago, before they got a handle on the situation.
"So the problem had been around for about a decade and the numbers had been relatively low, but increasing steadily and three years ago, they'd reached a peak of about 5.7 percent [in Canterbury]," Kaiser told Afternoons.
No more little burnt chippies?
The study pinpointed the insect's cycle and favourable conditions it needed to breed.
"We were able to start mapping them and identifying crucial times to spray them and then we started targeting the eggs and the nymphs rather than the adults, which had been previously the approach they've been taking. So we were able to encourage the growers to use softer chemistries which go for the eggs and the nymphs, and then we were able to get them to move their spray time forward as well."
But the researchers are also using "biological control agents" to fight off the bug, including pirate bugs and Tasmanian brown lacewing.
"These are natural enemies that you can release into the environment and they will take care of the pest naturally for you so you don't have to use chemicals.
"There were many different sites where it [the bug] was being found. Nine of them were hotspots where the numbers were very high, and we released the biocontrol agents around them and the numbers have crashed down to zeros and ones across the plains. Except for one site in Darfield, which we're still targeting.
"Being reliant on one natural enemy for one pest is always a dangerous situation to be in. So you're better off with having as much diversity out there to attack it from different angles. Some go after the eggs, some go after the nymphs and some go after the adults."
While it had been promising to see two years of low infections, eradication was unlikely, Kaiser said.
"I think it's going to be a case of keeping an eye on it, trapping for it, continuing to monitor, but also doing an augmented release of bio control agents every year."
He also noted a lot of quality control went into trying to ensure none of the affected crops ended up getting to consumers.