Further velvetleaf finds continue to pose a risk for New Zealand growers as concern is raised that the invasive weed may be falling off farmers’ radar.
Growers need to treat their farm gate as a border or risk the potential arrival of difficult-to-eliminate weeds such as velvetleaf, North Island velvetleaf co-ordinator Sally Linton said.
She said velvetleaf (Abutilon theophrasti) has “seemingly fallen off” a lot of growers’ radar.
“That’s because there has been a lot of hard work getting velvetleaf under control and there have been very few new incursions in recent years.”
But Linton cautioned that velvetleaf is still a risk, with its seeds remaining viable for 50 years.
“It only takes one inadvertent error for a seed to turn up on a new property. One plant can drop 30,000 seeds, so you do the math on what can happen by year two if that first plant is not found.”
She said finds on two new properties in Waikato in April are concerning as work to date has not thrown up any obvious leads for the source property.
“The worst-case scenario is there is velvetleaf on other properties that we do not know about.
“Being an annual weed we will now have to wait until spring and the new season before continuing our tracing efforts.”
Velvetleaf is a tall, large-leafed, highly competitive weed that is difficult to control because of its progressive emergence over summer.
Tracing has historically identified machinery and infested maize silage as the most common reasons for spread.
This demonstrates the need for continued vigilance by farmers and growers, as well as rigorous machinery hygiene protocols by the cropping sector.
As a declared pest, velvetleaf plants and seed must be removed and disposed of and legally cannot be moved off a property.
“This is not such a big deal if farmers are growing maize silage to feed to stock on their farm as there are pre- and post-emergent sprays that do a good job of keeping it under control, if you get the rates and timing right.
“However, if you are selling maize under contract for silage or grain, you have a big problem. It is your responsibility to confirm that there is not one velvetleaf seed in that crop before it is moved off.
“My understanding is that one of the new finds is returning the property to pasture as they’re not prepared to take the ongoing risk. So that’s about 30 hectares of maize lost to the industry,” Linton said.
An initial velvetleaf incursion, associated with maize growing in Auckland and Waikato, occurred more than 15 years ago and involved about 80 properties.
The scale of finds escalated in 2015-2016 with an incursion of contaminated fodder beet seed lines imported from overseas, sown on hundreds of properties across NZ, but predominantly in Canterbury, Otago and Southland.
South Island velvetleaf co-ordinator and Foundation for Arable Research biosecurity officer Ash Mills advises farmers on these properties to carry out routine surveillance.
This is especially important when paddocks are cultivated, as seeds can lie dormant in the soil and germinate years later.
In 2023, nine velvetleaf plants were found in a Mid Canterbury paddock that was associated with the earlier fodder beet incursion.
The 2015-2016 incursion prompted an extensive three-year project by FAR and AgResearch looking at management options for the control of velvetleaf.
This included alternative cropping choices, improved soil seed bank depletion practises and herbicide and non-herbicide control options.
Linton said to reduce the risk of spread, expect contractors or anyone coming on the property to be clean.
“If they [contractors] charge extra to do clean, put it down as an insurance cost; you can’t insure against biosecurity risk.
“Inspect your crops, call in any unknown weeds.
“One tip is the most likely incursion point is when the harvester turns in the gateway or where cultivating equipment starts working.
“Inspect those areas regularly as if you find one plant before it seeds you could well dodge a bullet.”
