Justice Venning's decision this afternoon came after a disputed facts hearing resumed to decide whether or not his offending was financially motivated.
Crown prosecutor Christine Gordon QC told the court Kerr was motivated by financial
gain, as he owned a rival pesticide called Feratox, for which he received annual royalties of $100,000.
The Crown argued he was strapped for cash, his bank accounts were at their maximums, he had extended the overdraft of his mother's account in "questionable" circumstances, and he was struggling to pay his bills.
Kerr's defence argued that although money was tight, that was because of spending in a company he was building called Natures Support - that makes possum fur belts for people with back problems.
That spending was discretionary. Take that away and he was "comfortably off", John Billington, QC, said. Kerr's position would not be worsened should that company fail as he had no financial liability to it such as guarantees.
Had 1080 been abandoned as a result of Kerr's blackmail attempts, he may have benefited in the short-term from an increased demand for Feratox.
"A small financial gain may have been the consequence but it was not the primary driver for an act of incredible stupidity and irrationality by someone who ought to know better," Mr Billington said.
Kerr was remanded in custody for sentencing on March 23.