Technical Yearbook 2023

MAY

Vineyard biodiversity – how to put it to work using cover crops By Geoff Gurr, Jian Liu & Jason Smith

This article is republished from Grapegrower and Winemaker , Issue 705, October 2022, with permission from the authors and Grapegrower and Winemaker .

Vineyards usually have a groundcover made up of spontaneously growing grasses and broadleaved weeds or have bare earth, either directly under the vines or across the whole vineyard. Each of these options has problems. Bare earth increases the risk of soil erosion by wind and water run-off and can lead to poor soil structure. Conversely, a weedy groundcover uses valuable water and requires mowing to prevent excessive growth. If the weeds are too vigorous, they can block air flow and favour development of fungal diseases and frost damage. Reflecting this challenging situation, there has been growing interest both in Australia and overseas in the use of alternative types of groundcovers. That’s where cover crops come in. These can be thought of as form of groundcover that is deliberately established and often more actively managed than a spontaneous coverage of weedy plants. Cover crops can deliver a range of benefits in the vineyard. Early work in South Australia, for example, showed scope for weed control using under-vine cover crops. In 2021, Wine Australia awarded funds to a new project that aims to generate evidence-based guidelines for using a range of cover crop types to deliver multiple benefits to vineyards. Results from the first year of this project, run by Charles Sturt University, are the focus of this article. One feature of the new project is the use of laboratory studies to assess the benefits of a range of potential cover crop plants to parasitic wasps that attack light brown apple moth, one of the key vineyard pests in many districts. The caterpillars of this pest damage bunches and leave them more susceptible to infection by botrytis fungus, leading to bunch rot. Our work has focussed on minute Trichogramma wasps that lay their eggs in the pest’s eggs, ‘hijacking’ them so they give rise to more wasps rather than developing into damaging caterpillars. Whilst Trichogramma wasps are widely distributed in Australia, they live for only a few days unless able to feed on nectar. Unfortunately, nectar plants tend to be scarce in vineyards making them

inhospitable locations for effective biological control. Our laboratory research has identified a range of plant species that may remedy this problem by providing nectar that is suitable for use by Trichogramma wasps. One example is buckwheat which produces nectar that extends the lifespan of these tiny wasps and more than doubles their egg laying. Buckwheat can be grown as a mid-row cover crop in vineyards but is too tall (about 1 m) to be suitable for use directly under the vines. Here, another plant, alyssum, seems to have good scope as it grows to only a quarter of the height of buckwheat. Alternatives to these exotic plants include several native species that might be favoured in settings where the manager wished to soften their overall environmental impact and make the vineyard a setting where native invertebrates and small animals find harbour. But our screening of various options has revealed an important practical message. Some native plants, including Acacia and Kunzea species, appear to provide no benefit to Trichogramma. Fortunately, many other species do greatly boost egg laying by wasps. These include the prostrate growing species Grevillia lanigera , Myoporum parvifolium and Leptospermum ‘Pink Cascade’. Our laboratory tests

Geoff Gurr checking early season establishment of buckwheat sown as a mid-row cover crop.

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TECHNICAL YEARBOOK 2023