Poor budburst and dying of single spurs in S. blanc and Cab. Sauvignon

The aim of this study was to investigate the cause of poor budburst and dying of single spurs in Sauvignon blanc (SB) and Cabernet Sauvignon (CS).

Project layout:

• Surveys of 17 affected SB vineyards and 19 CS vineyards were conducted and the incidence and severity of spur dieback was determined
• Ten dying spurs were collected from each vineyard to conduct fungal isolations from 2013-2016
• Field trials were conducted to determine the effect of the time of clean pruning on dieback of spurs, vine vigour and the incidence of trunk disease pathogens
• During the 2015 season, shoots in the three vineyards used for the clean pruning trial, were also examined for the presence of the bud mite, Colomerus vitis.

Results:     

• Isolation results show that grapevine trunk disease pathogens could be implicated in the poor budburst and dieback of spurs.
• Most of the dying spurs collected were observed to be associated with wounds made during clean pruning.
• The surveys also identified the improper use of wires, plastic clips and elastic bands/tapes/rope, which are used to train young vines as a significant contributor to dieback.
• The time of clean pruning did not have an effect on the budding and bunch formation of individual SB and CS vineyards.
• Examination of buds revealed differences in bud mite infestation among vineyards. High incidences of infestation by bud mite (>30 % of buds in each treatment), were found in the CS vineyard in Durbanville, followed by the SB vineyard in Constantia and very low infestation in the SB vineyard in Stellenbosch.

Significance of the study:

A number of factors contributed to the dieback phenomenon observed in SB and CS spurs, including grapevine trunk disease pathogens, bud mites, as well as viticultural practices. Environmental factors did not influence the occurrence of dying spurs as similar percentages were observed between the cooler and warmer areas. Treatment of pruning wounds is critical and highly recommended.

Researcher: Prof. Francois Halleen

Link to final report: http://www.sawislibrary.co.za/dbtextimages/HalleenF4.pdf

Image link: https://www.goodfruit.com/knowing-washingtons-trunk-diseases/