To date velvetleaf has been found in 11 regions on 250 properties.
Federated Farmers biosecurity spokesperson Guy Wigley says to find yet another line contaminated with velvetleaf is something more than a coincidence.
"All confirmed contaminated lines are via the same importer, DLF," he says.
"Farmers need to look very carefully at their feed source moving forward and carry out due diligence when looking at where to source their seed for the coming season."
The Ministry for Primary Industries (MPI) have advised that the contaminated lines of fodder beet seed include Kyros 128, Bangor 126, Bangor 079 and Feldherr 16UB131.
MPI is managing a nationally co-ordinated approach to the incursion and response.
Federated Farmers is urging farmers who have planted fodder beet seed this season to check their crops for the presence of velvetleaf.
"The horrendous cost of this incursion continues to mount - we need to take the appropriate measures to contain and potentially reduce the geographical spread over time."
If you suspect you have velvetleaf in your crops, please contact MPI's Pests and Diseases hotline 0800 80 99 66.
