MPI plants and environment surveillance manager, Mark Bullians, said it was unclear whether the fodder beet seed was contaminated or the weed was imported by another source.
Just one velvetleaf plant was found in a crop on a Parnassus farm.
DLF seeds and science manager Tom Bruynel confirmed the weed was found in a crop of Kyros fodder beet but said it was not clear how it got there. The fodder beet seed was imported from Europe where velvetleaf was not a pasture pest.
He said Velvetleaf seed could have come in feed bought because of the drought.
Velvetleaf is known to be present in Waikato. A single plant can produce up to 8000 seeds which will stay dormant until the following spring but in the right conditions can remain dormant for up to 60 years.
Bullians said it could be controlled with herbicide but that was another cost and task for farmers.
He said there was a legal requirement for any discovery to be reported to MPI via its hot line: 0800 809 966.
