A highly-invasive grass-weed is considered to be the worst pest of its kind for cropping farmers.
Broomcorn Millet is estimated to have already infested half of all sweetcorn paddocks in the country and is spreading quickly.
It is extremely fast growing and can produce shiny black seeds in as little as four weeks.
The Foundation for Arable Research says it is causing problems for farmers in the main sweetcorn-growing areas of Hawke's Bay and Marlborough, as it regerminates in regrassed paddocks after harvest.
Researcher Andrea Pearson says it poses very serious management problems wherever it is found.
Farmers are advised scout their paddocks for the weed and take action to get the seedhead out.
AgResearch estimates half of all sweetcorn paddocks already have the weed and expects it will spread to the rest unless transport precautions are taken.