Weeding out better wines

Chris Penfold inspecting weeds in one of the vineyards at Adelaide University's Roseworthy Campus.
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Chris Penfold inspecting weeds in one of the vineyards at Adelaide University's Roseworthy Campus.
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Wednesday, 29 November 2000

Australian red and white wines are about to become greener.

The nation's agriculture relies a good deal on its clean reputation. The lack of residual pesticides, herbicides and other pollutants has given Australia's food a high international standing, and a very valuable one commercially.

It's a reputation that needs constant vigilance. As Australian producers are increasingly aware, one contamination scare would do their food export trade a great deal of damage. In the wine industry, it could be devastating.

Already, a giant UK supermarket chain is questioning Australia's biggest wine producers about their use of herbicides that are known to contaminate ground water. Their wines are tested for such contaminants continually, but even anecdotal evidence of such herbicide use could cause significant damage to exports.

In that climate, alternatives to chemical pest control appear very attractive. Mr Chris Penfold, a Research Officer with Adelaide University's Department of Agronomy & Farming Systems at the Roseworthy campus is about to begin a comprehensive study of organic weed control in vineyards.

Funded by the Grape and Wine Research and Development Corporation, and supported by several local industries and a Californian equipment supplier, the project should produce valuable information on how to control vineyard weeds without the use of chemicals.

"Not all weeds are bad," says Mr Penfold, "but some might introduce disease to the vines, or act as habitat for insect and other pests. Mostly they simply compete with the crop."

A number of weed control measures will be trialled, he says.

"Cultivation is an obvious one, but cultivation can cause problems by breaking down the structure of the soil and exposing it to wind and water erosion. We will be looking at carefully timed cultivation with different implements, along with several other techniques."

These include "flame weeding", where a tractor-mounted device, fuelled by gas, heats the weeds to the point where their cell walls rupture. The use of flame weeding depends on the weed species present and management aims. The gas supplier, Kleenheat, will supply gas and equipment for these trials.

Mr Penfold will also investigate mulching vines, but even that technique has variables that must be tested separately.

"There has been quite a bit done already on mulching," says Mr Penfold, "but mainly to improve vine vigour and productivity while simultaneously reducing evaporation losses. Now we will see what it can do for weed control.

"Cereal straw mulch has commonly been used on vines, but as it decomposes it can compromise nitrogen availability. Other concerns are that it provides a habitat for mice, which then attracts snakes and endangers vineyard workers," he says.

The project will experiment with compost mulching, using mulch donated by Jeffries Soils and Peat's Soil.

As well as tending their vines, vineyard managers must also deal with the 70% of vineyard space that lies between the vine rows. These areas require treatments different from those applied to the rows.

"Some weeds in these areas can even be beneficial," says Mr Penfold. "They may help to fix nitrogen in the soil, soak up surplus water or even provide a habitat for predatory insects that prey on pest insect species and reduce their numbers."

The project will begin in the new year. Mr Penfold hopes that it will make a significant contribution to agricultural practice.

"In the long term, vineyard managers will need to have alternatives to herbicides in controlling weeds, and for organic growers, a wider range of strategies than are currently available will enhance the value of their production systems," he says.

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