Velvetleaf: Waikato farmers reminded to stay vigilent - Foundation for Arable Research

FAR biosecurity officer Ash Mills inspecting fall armyworm larvae damage. Photo / Foundation for Arable Research

Coast and Country’s Catherine Fry wraps the Foundation for Arable Research (FAR) projects happening around Waikato; including a warning to farmers to keep an eye on velvetleaf.

Velvetleaf (Abutilon theophrasti) seems to have fallen off many farmers’ radars.

That’s partly due to a lot of hard work getting velvetleaf under control, resulting in very few new incursions recently, says North Island velvetleaf co-ordinator Sally Linton (funded by regional councils and FAR).

Velvetleaf seeds stay viable for 50 years and it only takes one inadvertent error for a seed to turn up on a new property.

One plant can drop 30,000 seeds, so if plants aren’t found fast they can multiply quickly.

The initial velvetleaf incursion was more than 15 years ago, associated with maize growing in Auckland and Waikato, and involved about 80 properties.

With finds on two new Waikato properties in April this year, growers are advised to treat their farm gate as a border.

Linton understands that one of the new finds will be returned to pasture to minimise risk, meaning a loss of 30 hectares of maize to the industry.

“As yet, there is no clear source property identified for these two cases and because velvetleaf is an annual weed, we will have to wait until spring before continuing our tracing efforts.”

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

Continued vigilance by farmers and growers is needed, as well as rigorous machinery hygiene protocols in the cropping sector.

Maize establishment trial tackles difficult soil type

Waikato dairy farmer David Rawnsley said hosting the maize establishment trial gave him a first-hand look at no-till and minimum-till methods. Photo / Foundation for Arable Research

Waikato fourth-generation farmers sharemilkers David and Sarah Rawnsley are open to trying new ways of operating.

They are one of four Waikato farms involved in a four-year FAR maize establishment trial using no-till and strip-till cultivation.

The Rawnsleys’ farm and leased run-off have heavy marine clay, considered the most challenging of the soil types when using no-till techniques.

They moved away from maize silage because of pasture burn patches occurring after feeding out.

After consecutive dry summers and struggling chicory crops necessitated buying in maize, the Rawnsleys returned to growing 4.8ha of maize silage on the run-off in the 2020-21 season, when the trial started.

David seeks to improve profitability and meet evolving environmental standards.

Signage for the different types of tillage used on the Rawnsleys' farm. Photo / Foundation for Arable Research

Having the trial on his farm with its clay soil has been an educational journey.

Over the four years of the trial, average maize silage yields have been highest using full cultivation at 22.8 tonnes/dry matter/ha.

This is followed by sub-soil no-till with an average yield of 20.9 t DM/ha, no-till at 20 t DM/ha and strip-till at 19.7 t DM/ha.

Conditions over the four years have ranged from very dry to very wet.

FAR senior environment researcher Dirk Wallace said the key was selecting the right tool for the job.

Working with David allowed them to understand which tools work over multiple seasons on heavier soil.

“There is room to further improve profitability in each of these establishment methods as we refine what best practice looks like,” FAR senior field research officer Sam McDougall said.

“The Rawnsley trial results point towards increases in yield and gross margins in the cultivated and sub-soil no-till treatments, but these need to be weighed up against the potential for long-term soil quality improvements.”

Fall armyworm funding

Fall armyworm larvae is a plant pest that can feed on over 350 plant species, particularly sweetcorn and maize. Photo / Foundation for Arable Research

In June fall armyworm research received a boost from MPI’s Sustainable Food and Fibre Futures (SFFF).

A new project, led by FAR and supported by Vegetables NZ, covers a range of topics, including identifying economic thresholds for chemical control in maize silage, maize grain and sweetcorn; and investigating opportunities for integrated pest management.

Project leader FAR biosecurity officer Ash Mills said the economic threshold work was important, as the impact of FAW feeding damage varied between crop types.

Current control options for fall armyworm in New Zealand are limited to one insecticide (Sparta, active ingredient spinetoram) and a range of beneficial insects, with the Cotesia parasitoid wasp being the most active, although this can fall prey to insecticides used elsewhere.

Genetic work overseas already indicates Spartaresistance is likely present in New Zealand populations.

Managing this problem is where the economic threshold and Cotesia work intersects.

“We want to understand how much impact Cotesia sp is having on FAW as well as its relationship with other pest species and will use that information, alongside improved understanding of economic damage thresholds for the different crops, to develop an integrated pest management (IPM) programme for FAW,” Mills said.

In Australia the spread of fall armyworm has been rapid.

New Zealand and Australian researchers share notes, working together to manage fall armyworm.

Mills said New Zealand’s cooler climate resulted in significantly lower populations to date, so while Australian data was worrying, it didn’t necessarily mean the same thing would happen here.

“The Australian situation simply shows us that we should prepare for a future season where a larger more damaging population could create issues in maize and spill over into other crops grown in affected regions.”