Caution urged after weed discoveries

A weed pest falling off many arable growers’ radars is being brought back to their attention.

New discoveries of velvetleaf on Waikato properties in April have sharpened awareness of the risk.

Velvetleaf has been discovered on several Waikato properties.
Velvetleaf has been discovered on several Waikato properties.
An initial velvetleaf incursion, associated with maize growing in Auckland and Waikato, spread to about 80 properties more than 15 years ago.

This escalated in 2015-16 when contaminated fodder beet seed lines imported from overseas were sown on hundreds of properties mainly in Canterbury, Otago and Southland.

In 2023, nine velvetleaf plants were found in a Mid Canterbury paddock which was linked to the earlier outbreak.

North Island velvetleaf co-ordinator Sally Linton said in a statement growers needed to treat their farm gate as a border or risk the potential arrival of difficult-to-eliminate weeds such as velvetleaf.

"Velvetleaf [Abutilon theophrasti] has seemingly fallen off a lot of growers’ radars. 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."

Investigations into the April discoveries had yet to throw up any obvious leads for its source, she said.

"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 which is difficult to control because of its progressive emergence over summer.

Tracing has historically identified machinery and infested maize silage as the most common source for its spread.

As a declared pest, velvetleaf plants and seed must be removed and disposed of and legally cannot be moved off a property.

The owners of one of the new properties found with the pest is understood to be returning about 30 hectares of maize to pasture as they’re not prepared to take the ongoing risk.

Foundation for Arable Research biosecurity officer Ash Mills said farmers should carry out routine surveillance, particularly when paddocks were cultivated, as seeds could lie dormant in the soil and germinate years later.

The 2015-16 incursion prompted an extensive three-year project by the FAR and AgResearch looking at management options for control of velvetleaf. This included alternative cropping choices, improved soil seed bank depletion practices and herbicide and non-herbicide control options.

 

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