With the defendant obtaining 10 per cent in royalties from each sale, that would put him in line for a large windfall.
Kerr has been convicted over the threats, which saw infant milk formula pulled from supermarket shelves, but disputes some of the Crown's allegations.
Those facts at issue are the subject of a hearing before the High Court at Auckland this week.
Kerr's police interview from October was played in which he denied any role in the plot to have 1080 withdrawn from use.
When asked if he had ever written to Fonterra or Federated Farmers he replied: "No, never."
Detective Senior Sergeant Aaron Pascoe asked him why he thought anyone with such an agenda would address their concerns with those two organisations.
"I've no idea. That's a strange one," Kerr said.
Ms Gordon said Feratox sales were on the slide and the income was not enough to live on.
At the time the threats were sent, Kerr's credit card was almost maxed out and he could not make the minimum repayments, she said.
In a police interview, he downplayed the issues saying it was his royalties totalled $100,000 a year and he was "not in any stress".
One witness told the court a 1080 ban would see a rise in the use of Feratox by as much as 30 per cent.
And former colleague Graham Wright spoke about Kerr's preoccupation with money.
"He was always dreaming about boats and holidays and always talked about spending money . . . Money was in the background of everything he did," he said.
"I'd describe his spending as extravagant. He would buy the biggest and best machinery; much more than we needed."
An ANZ staffer also told the court about Kerr increasing an overdraft facility on his mother Judith's account from $10,000 to $50,000, which he was permitted to do since he had enduring power of attorney over her estate.
When the bank contacted Mrs Kerr she "knew nothing" but they approved the application after the defendant provided them with documentation about his authority.
The Crown says Kerr typed the blackmail letters and produced address labels himself, as well as mixing the infant formula with the 1080 and splitting it between the two envelopes while wearing gloves.
He allegedly drove to Marton one night and posted the two packages from Paraparaumu.
A criminal investigation started when they were received by Fonterra and Federated Farmers in November 2014 threatening to poison infant formula if New Zealand did not stop using 1080 by the end of March.
The public was told of the threat in March and formula was taken off supermarket shelves and held securely to prevent contamination.
In what became known as Operation Concord, 60 people were considered of significant interest and approached to be interviewed by police.
More than 2600 people were considered over the course of the investigation, which cost police $3 million, Police Commissioner Mike Bush revealed when the man was arrested in October.
Police said they believed the arrested man acted alone and no one else has been charged.
Blackmail is punishable by up to 14 years in jail.
The letter
Mr T Spierings, CEO Fonterra
Mr G Smith, CEO Federated Farmers
NOTICE - Sodium flouroacetate (1080)
Enclosed is a sample of 1080 blended with New Zealand dairy infant formula currently in China.
If after March 27, 2015, this VTA [vertebrate toxic agent] is still in use in New Zealand, several New Zealand infant and other formula will be released into the retail chain in the Chinese market and one other market with traces of 1080.
The release will coincide with a media package applied to the Chinese authorities and competitors highlighting the risk to New Zealand, their environment and others consuming our export products, from exposure to 1080, and current New Zealand government agency policy and practice with 1080.
A concurrent media release in New Zealand and China will expose the past 30 years of flawed self-serving science and beaurocracy that has allowed the government's sanctioned approval to continue.
Our group has no confidence in the political or democratic process concerning 1080.
It is for you to manage the outcome.
This notice is private and confidential to you and will remain as such.
If there is no compliance it will be part of the media release.
The magnitude of this issue is now beyond the temporary financial and personal sacrifice that will be made by the agricultural and tourism sectors of the New Zealand economy.
What is Feratox?
• Unlike 1080 it has to be distributed by hand at bait stations
• It is more expensive to produce than 1080
• Cyanide in the pellets combines with a possum's saliva to produce cyanide gas, which kills the animal in a couple of minutes. 1080 can take days to kill a possum
• Because of its quick-acting properties, the pelts of the possums can be more easily gathered and used
• Kerr makes 10 per cent royalties on all sales
• A man involved in Feratox's manufacture said it was a "natural replacement" for 1080 and its use could rise by up tp 30 per cent if 1080 was outlawed
