Transient Heat Therapy Has Few Effects on Grapevine Performance in the Okanagan Valley, British Columbia, Canada

Background and goals The goal of this study was to evaluate a commercially available machine (Agrotherm XT, Agrothermal Systems) for transient heat application to enhance vineyard canopy temperature during the growing season and to study the effects of transient heat application on grapevine performance, phenology, and berry quality.

Methods and key findings Heat was applied up to six times during the growing seasons in 2019 and 2020 in three vineyards located in East and West Kelowna in the Okanagan Valley in British Columbia, Canada. Shoot and cluster counts, bud fruitfulness, grapevine phenology, leaf greenness, harvest, pruning weight, and crop load data were collected each year. Results showed that transient heat application is not an effective management practice. Results were not consistent among vineyard locations or growing seasons. In 2019, treated Merlot vines had fewer berries per cluster but higher juice pH, and treated Chardonnay 2 vines had reduced leaf greenness but higher pruning weight. In 2020, treated Merlot vines had reduced leaf greenness but higher pruning weights, and treated Chardonnay 2 vines had reduced leaf greenness but higher berry weights and soluble solids. In 2021 only, treated Chardonnay 2 vines had greater fruitfulness (clusters/shoot).

Conclusions and significance Heat treatment had inconsistent effects on grapevine performance and berry quality and no changes in grapevine phenology were observed. Given the high purchase costs, transient heat therapy is not an effective management strategy to improve grapevine performance and berry quality in the north central part of the Okanagan Valley in British Columbia.