Purchased Maize Identified as Likely Source of Velvetleaf Incursion
Tracing has indicated that the source of the first velvetleaf find of the 2025-26 crop season, in Auckland, was likely maize purchased in the Waikato region.
Rural News took a trip to the Taranaki earlier this month to witness detector dog Wink and his handler John Taylor on the hunt for the aggressive weed that Robbie Sicely, biosecurity manager at Horizons Regional Council describes as "the world's most cropping weed".
Velvetleaf is highly competitive and aggressive in crops such as maize and fodder beet, with studies showing that crop yields are reduced by up to 70%. Even moderate infestations that emerge simultaneously with the crop can reduce yields by as much as 25%.
Taranaki has 13 infected sites and Wink and his handler Taylor, of K9 Weed Detection searched maize or chicory crops.
Initially, Wink appeared to be covering areas in a random pattern, not unlike a sheepdog looking for sheep, but quickly became more focused when he scented the pest plant. He eventually zeroed in on a plant, barked to indicate his find, then sat to highlight the area.
At a command from Taylor, Wink then began a much more structured search pattern in the immediate idea, looking for further plants that had germinated from seeds disturbed by recent cultivator movement.
Following the recent maize planting regime in the North Island, disturbed soils offer an ideal environment for what may have been long dormant seeds to germinate.
Read More:
- Velvetleaf Threat: North Island growers urged to stay vigilant
- Velvetleaf a real risk to crops
- Vigilance over Velvetleaf
North Island velvetleaf co-ordinator, Sally Linton, reminded growers that given its potential to decimate the New Zealand cropping sector, the economic “ripple effect” could affect the dairy, food production and export sectors.
“Fighting velvetleaf is a shared responsibility that everyone needs to be involved with, including the grower, their neighbours, contractors and seed merchants,” said Linton.
“Currently, we are just about treading water, but if we let things slip, Velvetleaf has the potential to get away from us.”
An annual weed, typically active between October and April, the invasive broad-leaved weed has been identified in over 100 North Island properties, largely in the maize crops of Auckland and the Waikato. Of particular interest to the assembled growers were 13 known incursions in the Horizons region, likely occurring on the arrival of fodder beet to the area following the wider 2016-17 fodder beet incursion in the South Island.
Emerging as a seedling, the weed quickly matures by around 100 days, identified by large heart-shaped leaves, buttery yellow flowers of about 3cm across and the eventual arrival of distinctive black seed pods of 2.5cm diameter, made up of 12-15 segments. Of particular concern is the fact that a single mature plant, that might grow to 1.2 to 1.5 metres high, can produce up to 30,000 seeds, which can survive for up to 50 years.
Linton said, “Looking at maize crops taken for silage, the seeds are not killed during the heating process of ensiling. Indeed, the use of feed pads, that in turn lead to feed waste and effluent washing, means that viable seeds can easily be spread over a wide area of a property, without realising.”
Linton suggested that anyone buying-in silage, should be inspecting source crops ahead of harvesting and confirm with suppliers that the property was velvetleaf-free. They should also confirm from harvesting contractors whether they had worked at infected properties, and if this was the case, were up to speed with appropriate hygiene practices, before moving to the next job.
The weed spreads mainly through contaminated maize, fodder beet, machinery, and livestock, so farms are at risk if neighbouring properties or purchased crops are contaminated.
The economic consequences go beyond individual farms. Infestations threaten crop quality, reduce marketable yields and can undermine domestic and international confidence in agricultural production if not controlled promptly.
Control needs to be centred around postemergent spraying, pulling juvenile plants or bagging mature specimens and safely disposing of infested material, especially when seeds are mature.
