Fungicide Application in Young Vineyards Protect Pruning Wounds from Grapevine Trunk Diseases and Provides Long-Term Economic Benefit

Fungicide Application in Young Vineyards Protect Pruning Wounds from Grapevine Trunk Diseases and Provides Long-Term Economic Benefit

Carmen Gispert, UCCE Viticulture Farm Advisor Riverside County

Jonathan Kaplan, Department of Economics, Sacramento State University

Philippe E. Rolshausen, UCCE Specialist, Department of Botany and Plant Sciences, UC Riverside

Grapevine trunk diseases (GTDs) including eutypa dieback, bot canker, blackfoot disease, young vine decline, and esca (also known as grape measles), limit the profitable lifetime expectancy of vineyards. Growers are well aware of the negative impact of GTD on vineyard productivity and have consistently ranked them as a research priority for the industry. Fungicide application on the pruning wounds of young vines is recognized as an efficient practice to minimize GTDs incidence and is most beneficial when implemented in the first years after the vineyard has been established (Figure 1).

However, stakeholder surveys suggest that few growers follow these guidelines. Further these surveys have shown that the first fungicide applications often coincide with the initial spur or cordon dieback when vineyards turn 8-10 years of age. The long incubation period between the initial infection and the first symptom appearance often gives growers a false sense of security, leading to an excessive delay in the use of GTD-protective fungicides. Delayed application of GTD fungicides provides short-term production cost savings but results in long term yield reduction and shortens a vineyard’s productive life.

In 2012, we started a survey in the area following several farm calls from growers that experienced a high incidence of GTD in young vineyards with typical wood dieback, declining  vigor, and apoplexy (Image 1). These observations were at first unexpected because the pathogens causing these diseases require rainwater to sporulate and become airborne and the arid conditions of the Coachella desert are not conducive to the spread of these pathogens. However, local growers use overhead sprinkler irrigation during the winter months to help satisfy chilling requirements. This process overlaps with vine pruning, creating suitable conditions for new GTD infections. In addition, when establishing a new vineyard, growers used to interplant the new vines between the old stumps left from the previous vineyard (Image 2). This allows the old wood to act as a reservoir for pathogens. The stumps coupled with the overhead sprinkler irrigation creates the perfect environment for fungal spores to become airborne and infect the exposed pruning wounds on young vines.

To combat this issue, we conducted a long-term study to evaluate the effect of applying pruning wound fungicide application in young vineyards under high disease pressure (with vine stumps) on GTD incidence and productivity. The field experiment started in 2014 in a commercial two-year-old vineyard Sugraone located in the desert of Coachella Valley. Each winter, vines were manually pruned, and one half of the vineyard was tractor sprayed on the second day after pruning with the California industry standard Topsin-M® (a.i., thiophanate methyl) at the recommended label rate for six consecutive years. The other half of the vineyard remained unsprayed for GTD across all 6 years.

Image 1. Young vines collapse (aploplexia) caused by Grapevine Trunk Diseases

Image 2. New vineyard inter-planted between old vine stumps.

Image 3. Symptoms caused by GTDs (black streaks of esca) in a grapevine cordon.

After 6 years, we randomly pruned the cordons and spurs of 150 vines (10 vines per row in a total of 15 rows in both control and treated blocks) and inspected them for symptoms of GTD and scored the number of vines with symptoms (i.e., wood discoloration, streaking or necrosis; as seen in Image 3). We also recorded the yield of 25 individual vines selected randomly within those 15 rows in both the treated and untreated blocks. Finally, we estimated the economic benefits of post-pruning fungicide application.

Thiophanate-methyl pruning wound treatments reduced disease incidence and increased yield (Figure 2). After six years of post-pruning fungicide applications GTD incidence was reduced by half (from 40% to 20%) and yields were increased by 40% (from 19 to 27 lbs. per vine). According to our economic analysis, the benefit from spraying in year 2 and beyond was calculated at just over $85,000 per acre over a 25 year vineyard lifespan for the 50% disease control scenario, which is equivalent to a benefit of more than $3,400 per acre and per year.

This study has helped table grape growers in the Coachella desert with decision making to effectively manage GTDs. Over the course of this trial, growers were more diligent about removing old vine stumps before planting new vineyards. In addition, many more applied Topsin M® on vines soon after pruning. In view of the economic benefit, this study provides wine, table, and raisin grape growers convincing evidence in support of early adoption of post-pruning fungicide application to manage GTDs.

Acknowledgments: This project was funded by the California Desert Grape Administrative Committee and in part by the USDA-NIFA Specialty Crop Research Initiative Grant#2012-51181-19954 awarded to K. Baumgartner (USDA-ARS, UC Davis). We would like to thank ‘Anthony Vineyards’ for providing a commercial vineyard to conduct the research and for the assistance with the tractor application of fungicide and crop harvest.

References

Baumgartner K. et al. Managing Grapevine Trunk Diseases in California's Southern San Joaquin Valley. American Journal of Enology and Viticulture, 2019. 70(3): p. 267-276.

Hillis V. et al., Preventative Disease Management and Grower Decision Making: A Case Study of California Wine-Grape Growers. Phytopathology, 2017. 107(6): p. 704-710.

Kaplan J. et al. Identifying Economic Hurdles to Early Adoption of Preventative Practices: the Case of Trunk Diseases in California Winegrape Vineyards. Wine Economics and Policy, 2016. 5: p. 127-141.

Norton M. et al. An Economic Analysis of Preventative Practices for Managing Trunk Disease in Table Grape Vineyards. SCRI Trunk Disease Project Research Brief. http://treeandvinetrunkdiseases.org/wp-content/uploads/2017/06/170612_CTGC.pdf. October 2020.

Rolshausen P.E. et al. Evaluation of Pruning Wound Susceptibility and Protection Against Fungi Associated with Grapevine Trunk Diseases. American Journal of Enology and Viticulture, 2010. 61(1): p. 113-119.