Saturday, December 2, 2023

Herbs take on weeds in orchard trial

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Search is on for plants that will reduce need for herbicides under fruit trees.
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A battle is underway in an apple orchard in Motueka as researchers watch to see if ground-cover plants will see off weeds and reduce the need for herbicides.

The trial is one of 12 projects to gain funding from the Rural Professionals Fund established in 2020 by the Our Land and Water National Science Challenge to support projects that could lead to significant improvements in farming systems and benefit farming communities.

In the Motueka study, herbs and forage species have been planted under apple trees in a Nelson apple orchard.

AgFirst, Willisbrook Orchard, New Zealand Apples and Pears Inc (NZAPI) and Plant and Food Research in Motueka are all involved in the trial.

AgFirst Motueka consultant Aimee Lister says current orchard practice is to use herbicide sprays under trees to remove competition for nutrients and water from unwanted weed plants.

This has been a reliable and cost-effective management practice, but it leaves the ground bare, susceptible to erosion and with overall reduced soil health. 

Ground cover has been effective with a lot of other fruit species, especially grapes and citrus, but not so much with apples.

“It’s always been an interest of mine so here’s the chance to look at alternative low-growing ground crops to reduce the use of herbicides,” Lister says. 

The industry aims to significantly reduce chemical use by 2050.

“This project aims to contribute knowledge to the goal of eliminating the need for herbicides in future.

“The date is just a target and it is important to look for alternative effective management practices.” 

The trial got underway on October 1 on Willisbrook Orchard at Hope, near Nelson. 

Seed beds were established and seven different seed species planted under two rows of apple trees, each row 100m long.

The advent of new-age canopy systems with trees growing in a 2D configuration, as opposed to in a traditional vase shape, means more light now reaches orchard floors. This makes it easier for weeds to grow but also provides the conditions for the species used in the trial to become established.

“We had a viticulturalist help select plant species which were deemed to have the best attributes, including that the seeds were readily available, they were low growing, spread easily and were perennial.”

Each species has been planted separately to be able to measure how each performs and how they interact with the soil and trees.

The species selected are sheep’s burnet, a deep-rooted perennial herb; bird’s foot trefoil, a member of the pea family; plantain, a herb with a fibrous and coarse root system; strawberry clover, a perennial clover that performs well in hostile conditions; alyssum, a compact perennial flowering plant; chicory, a hardy perennial; and common yarrow, a flowering, low-growing plant.

The initial trial is for nine months.

Lister acknowledges it is a short timeframe for the trial, but says it is hoped enough information can be gained to establish if all or some of the plants effectively out-compete weeds, reducing the need for sprays without having any detrimental effects on the trees and the fruit they produce.

The trial has the potential to grow into several years to cover resulting soil health and quality and tree health. “We have the support of NZAPI and Plant and Food Research, who will help with gathering the scientific information needed to understand the species which perform best.”

The research will include sampling leaves and fruit, both from fresh fruit and stored fruit, to find out if the ground-cover plants compete for nutrients with the trees and if there are any implications for increased pest and disease pressures.

Soil samples were taken before the trial began and sampling will be continued throughout the trial period to find out if there are any differences in soil microbiology. 

Control samples will also be taken from trees and from the soil of orchard rows managed under the traditional weed-spray strip system.

The project met with a few initial challenges, including finding machinery to prepare seed beds and plant the seeds, and installing irrigation to ensure the cover crops survive.

“We were able to find a vineyard contractor who had a machine which could prepare the seed bed between the trees, but there is very little orchard equipment capable of working under apple or pear trees.” 

If the trial is successful and the concept widely adopted, then the equipment needed to prepare the seed bed and plant the seeds will no doubt emerge, Lister says.

While the focus is to control weeds under trees, the trial will also monitor how the ground cover reduces soil erosion, which will be particularly relevant for orchards on hillsides.

“There has been quite a lot of interest in the trial from the industry and we will be keeping growers up to date with its progress through regular NZAPI field days.” 

The trial fits well with AgFirst’s vision to enhance sustainability within its own business and that of its clients.

“The ideal result of the trial would be that at least a couple of the plant species do well and quickly establish ground cover which excludes weeds but does not compete too much with the pipfruit,” Lister says.

“If we can prove the use of ground-cover species works, the practice is easy and cheap to use without creating additional labour costs and it reduces expenditure on herbicides, then ultimately we would like to see the practice more widely adopted within the industry.”

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