A Review of Cultural Practices for Botrytis Bunch Rot Management in New Zealand Vineyards

Abstract

Botrytis bunch rot of grapes (BBR) causes substantial crop and wine quality issues globally. Past and present foundations for BBR control are based upon synthetic fungicides and varying forms of canopy management. Many authors regard the continued dependence on fungicides as unsustainable and have urged greater deployment of cultural, biological and nutritional strategies. However, in contrast to organic wine production, the uptake of alternative strategies in conventional vineyards has been slow based on cost and perceived reliability issues. This review summarises research from many different wine growing regions in New Zealand with the aim of demonstrating how traditional and newly developed cultural control practices have cost-effectively reduced BBR. In addition to reviewing traditional cultural practices (e.g., leaf removal), mechanical tools are described that remove floral trash and mechanically shake the vines. Multi-omics has improved our knowledge of the underlying changes to grape berries after mechanical shaking. Exogenous applications of calcium may correct calcium deficiencies in the berry skin and reduce BBR but the outcome varies between cultivar and regions. Nitrogen aids in grapevine defence against BBR but remains a complex and difficult nutrient to manage. The sustainable growth of organics and The European Green Deal will stimulate researchers to evaluate new combinations of non-chemical BBR strategies in the next decade.

Wind speed, sun exposure and water status alter sunburn susceptibility of grape berries

“…Exposure of grape berries by leaf removal enhanced their resilience to heat damage. Leaf removal after bloom time is a common practice to prevent fungal diseases (Mundy et al, 2022), and our study demonstrated that it lowers the berries' susceptibility to sunburn after an acclimation period of about 7 days. The same effect was shown for both early (pea size) and late (lag phase) defoliation.…”

Assessment of microbial biocontrol agent (BCA) viability to mechanical and thermal stress by simulating spray application conditions

“…Traditionally, management of these fungal diseases relied on viticultural practices, such as pruning and defoliation, and specific training systems to improve ventilation and air circulation to reduce canopy humidity and inoculum sources, and using synthetic fungicides 1,2 . However, the use of synthetic fungicides is not considered sustainable owing to recurring rapid development of resistant strains of the pathogens and because of adverse effects of the fungicides on the environment and human health 3 . The presence of residues can furthermore negatively affect wine quality 4 .…”

“…Bacteria belonging to the genus Bacillus and fungi belonging to the genus Trichoderma are two of the most important groups of microorganisms used to control fungal pathogens in numerous crops 11–13 . Although BCAs were successfully implemented, their efficacy is generally more variable compared to synthetic fungicides 2,3 . This is not surprising, given that BCAs are living organisms dynamically interacting with the target pathogen, the host plant and the microbial communities present on the host surface in a changing physical environment.…”

“…1,2 However, the use of synthetic fungicides is not considered sustainable owing to recurring rapid development of resistant strains of the pathogens and because of adverse effects of the fungicides on the environment and human health. 3 The presence of residues can furthermore negatively affect wine quality. 4 These concerns have led to the search for alternatives to the use of synthetic fungicides.…”

“…[11][12][13] Although BCAs were successfully implemented, their efficacy is generally more variable compared to synthetic fungicides. 2,3 This is not surprising, given that BCAs are living organisms dynamically interacting with the target pathogen, the host plant and the microbial communities present on the host surface in a changing physical environment. For example, (micro)climatic conditions, such as temperature and relative humidity, have a major effect on the efficacy of BCAs.…”