Bug warfare at century-old Sydney rose garden to help deter pests

Once considered a form of "black magic", an army of predatory insects is being used to tackle pests in a popular century-old Sydney garden.

Centennial Park in the city's east was formerly a swamp that was turned into a drinking water source, before it was transformed into parklands and opened to the public on Australia Day in 1888.

About 20 years later, then-park director Joseph Maiden planted a rosarium, which in Latin means "rose garden".

Today, it is home to 33 different varieties of roses, with an estimated 800 plants overlooking Busbys Pond.

Geese are often seen walking among the floral bursts of colour, giving it a somewhat fairytale appearance.

Unfortunately, it is not just humans and birdlife that enjoy the sweet scents. Pests do too.

A team of ladybirds and parasitic wasps, led by Western Sydney Parklands senior horticulturalist Tristan Harman, have been tasked with managing "a fairly heavy aphid infestation".

Mr Harman said it was normal for new shoots to attract thousands of the bugs each year after the roses were pruned back in winter, but they had to be managed.

"They're pretty amazing survivors, like they pump out clones if they need to."

Aphids can cause roses to become distorted and puckered. The pest can also pass on viruses between plants.

They are also quite unsightly, often encouraging black mould to develop.

Although aphids can significantly damage roses and other plants, they are no match for the thousands of "gruesome" predatory parasitic wasps.

"Then the wasp, once it's done that, goes on to complete its life cycle, goes into its adult phase."

About 1,000 ladybirds, otherwise known as ladybugs, are far tamer in comparison and easier to spot, eating the aphids as they appear.

The insects are released annually, and this is the second time Mr Harman has been in charge.

Five batches are distributed among the garden beds from September to early November: two in the first fortnight, then every fortnight after.

After just the second release this year in late September, Mr Harman said the insects were victorious in their conquest.

The ladybirds and three types of parasitic wasps, including their eggs, were supplied and sent to Sydney by a company based in South Australia.

"They're in a little polystyrene sort of esky type thing with a tiny little cooler bag thing in there that keeps the insects cool," Mr Harman said.

"The wasps are in vials and the lady beetles are in a little ice cream container ... and they send them out with shredded newspaper.

"As long as you get them out within a day or two of their arrival, they're fine."

The delivery included wasp eggs and live adult insects.

"It was decided that it's obviously better to use an integrated pest management plan rather than just spraying with toxic chemicals for every possible pest disease," he said.

Mr Harman said this year's batch cost about $1,300, but came with added benefits.

"I think it would probably work out comparable in the overall growing season to be releasing these insects, especially when you think of some of the chemicals you can use that are toxic to bees," he said.

Mr Harman said when he was studying almost 30 years ago, using predatory insects to deal with pests seemed like "some sort of black magic".

"In previous jobs I've had, there was never any talk of using these sorts of methods, even though it was something that, after, 15, 20 years, it was something that was common," he said.

"You got these beautiful little insects walking on you and you put them on the flower and they go and they do their thing and they're part of what's beautiful in the garden.

Mr Harman said about 17 million people visited Centennial Park each year, including those attending weddings.

"So we try to keep it at its highest standard as we possibly can without spraying unless we absolutely have to," he said.