The invasive weed velvetleaf has been found on more farms in Waikato, prompting the Waikato Regional Council to ramp up its local response.
Velvetleaf has already been found in infested fodder beet crops in several parts of Waikato.
The council said it had since received information about an additional five infestations, marking a significant escalation in the scale of the velvetleaf spread in the region.
It said it appeared to be related to the movement of infested maize or maize silage, particularly in the North Waikato, Matamata-Piako and South Waikato districts.
Council staff were also inspecting a further 14 sites, where it was suspected velvetleaf might be growing.
The weed stands well above a beet crop, and has distinctive large, velvety, heart-shaped leaves.
Velvetleaf seeds can remain viable for up to 60 years.