It grows to about a metre high, has very short-lived buttery yellow flowers, distinctively segmented seedpods and large heart-shaped or circular soft leaves that have an unpleasant odour when bruised.
Each plant can produce thousands of seeds that stay alive in the ground for years.
Massey University weed expert Dr Kerry Henderson said that once velvetleaf is here, "the horse has bolted".
People finding suspected velvetleaf should photograph it, mark the location and contact MPI or NRC staff who will remove the plants. Landowners or growers should not pull up plants or graze stock in infested crops.
The highly competitive plant was first found in New Zealand growing amongst fodder crops on a Waikato farm in 1978, having arrived in contaminated imported seed, but was contained to only a few sites. This latest heavy incursion is far more widespread.
MPI has directed grain and seed retailers who have sold the Kyros and Bangor beet seed to hold any remaining seed in stock and to instruct customers to return any unsown product. Growers who have unsown seed should return it to the retail outlet.
Velvetleaf has been grown in China and northern India for thousands of years for its jute-like fibre, and edible seeds.
