"I can remember shooting my first wallaby 60 years ago and they've really ballooned since that time," he told RNZ's Country Life.
"The more sweeter you get your country, the more wallabies you're going to get."
For farmers, one of the main issues with wallabies was they ate quality feed that was intended for sheep, which could have a big impact on stocking ratios and lambing rates, Walter said.
"Three wallabies to a sheep, that's how much they eat."
He reckoned having wallaby-free areas on the farm could increase returns by $50,000 or $60,000 depending on merino wool prices.
Now that poisons were being used to control the pesky marsupials, Walter felt like they were starting to get on top of the issue.
As part of MPI's National Wallaby Eradication Programme, pellets of the poison 1080 have been dropped onto Wainui Station. For Walter, this had been a game-changer.
"When we poisoned, it enabled us to run another 1000 or 1500 stocking units (sheep)."
He'd like other landowners with wallaby-ridden properties to follow suit and apply for a 1080 drop but was aware some people weren't keen on having the controversial poison on their property.
"Ï fully understand those people's feelings about what it does but the thing is we're not dealing with a natural animal, we're dealing with an introduced species into New Zealand that's also having an impact on our native plants.
"There are still thousands of wallabies sitting around on this land and if left unchecked they are going to create a real issue in future years," he said.
