New Zealand winegrowers have been increasingly concerned about the impact of weed management practices in the undervine area on soil health, specifically soil microbial health.
Application of herbicides containing glyphosate is the most widely used tool to limit plant and weed growth in the under-vine area.
However, a growing perception of a negative effect of glyphosate on human and environmental health has prompted winegrowers to consider alternative methods of weed control, such as undervine mechanical weeding.
While mechanical weeding does eliminate the need for chemical intervention it does not come without its disadvantages, including an increase in diesel consumption and labour requirements. The continuous physical disturbance of the soil under the vine also has negative impacts on soil health, including soil compaction and a decline in soil structure and soil biological communities.
Lately it has become common practice to combine herbicides with biological products in an effort to decrease the negative impact of herbicide application on soil health. This practice is known within the industry as herbicide buffering.
One of the Bragato Research Institute’s long term strategies is to drive research, innovation and growth across a number of highly technical issues that impact New Zealand winegrowers, including vineyard sustainability and the impacts from pests, diseases and a changing climate.
While growers are concerned about soil health, they are also concerned about how changes to weed management practices will impact on yield and quality.
While many studies have explored the effect of weed management practices in various agricultural production systems on soil health, no studies have compared the effect of common weed management practices in the undervine area in New Zealand.
A research project looking into microbial responses to undervine treatments was carried out in a Marlborough vineyard in 2021 and 2022.
The aim of the trial was to understand the impact of different ways of controlling under-vine vegetation over the course of the grape growing season. The effect the various undervine treatments had on yield and juice was investigated as a secondary aim of the research.
Under-vine treatments included in the trial were control, herbicide, buffered herbicide and weeding.
Soil samples were taken by Bragato Research Institute at three time points: before application of treatments in mid-September, two weeks after treatments were applied (late-September) and six months after treatments were applied (mid-March).
Samples were sent to Manaaki Whenua – Landcare Research, who conducted and interpreted phospholipid fatty acids (PLFA) and neutral fatty acids (NLFA) analyses, to compare the effect different under-vine treatments had on soil biological communities.
Findings from the first year of research showed that reducing under-vine vegetation using herbicides or weeding had a detrimental effect on arbuscular mycorrhizal fungal abundance, potentially reducing the benefits grapevines receive from this mutualism.
Based on this result we have learned we need to diversify our undervine management practices to include cultivation of beneficial plant species in the undervine area. We are hoping to invest in this area this coming financial year.
The trial was funded with MBIE Regional Research Institute (RRI) funds for the first year of the project, significantly helping jumpstart BRI’s soil research and enabling BRI to gain financial sustainability and build capability. BRI is now in the second year of research, which is funded with MBIE RRI transition money.
