Improved control of bunch rots in Granite Belt winegrapes

Abstract

Improved control of bunch rots in Granite Belt winegrapes

Summary

This report details project work carried out during the 2001/2002 season. The Granite Belt Wine Industry Association sought to extend similar work being conducted in the South Burnett as control of bunch rots was also an important issue for the region. The association contracted DPI’s Queensland Horticulture Institute through its Applethorpe Research Station to plan and conduct the work and sought and received funding through GWRDC’s RITA program.

Project activities included a survey of Chardonnay and Shiraz blocks to identify the range of bunch rots organisms present and assess their incidence, severity and relative importance for yield and fruit quality. Vineyard training activities and a review workshop were used to increase grower awareness and understanding of bunch rots. An interstate specialist in bunch rots was obtained as guest speaker at the workshop.

Two syndromes (referred to as “Dry Berry” and “Shrivel Berry”) and Botrytis affected both varieties. In the case of Shiraz, “Dry Berry was by far the most significant problem. Although an Alternaria sp. was nearly always associated with the syndrome, its cause remains unclear. Its main impact seems to be in reduced yields while its affect on wine quality at this stage appears minimal. “Shrivel Berry” appears to be related to water stress post veraison.

A Colletotrichum species was found at low levels in most vineyards. Discussions with SARDI pathologist Barbara Hall and a CSU student involved in work on this organism indicate that almost certainly it is C. acutatum. Its incidence varied widely between blocks of both varieties. There is concern that this organism may cause serious problems in vineyards and wine production under wet conditions at harvest. At present the fungus is not well understood and control strategies are still being developed and tested. Urgent consideration and support should be given to investigate this organism.

Botrytis was generally well controlled in most vineyards. Below average rainfall, especially in the pre-harvest period did not provide conditions conducive to its development. Very high levels in two vineyards inflated district averages in both varieties and indicate the potential problem this disease poses if ineffective control programs combine with wet weather.

The spray programs used by growers showed that their basic understanding of control strategies for bunch rots was not as good as expected. Presentations at the review workshop by guest speaker, SARDI pathologist Barbara Hall highlighted issues of chemical selection and timing that should be addressed with training and information resources. Most growers did not recognize Colletotrichum in the field. The interaction with DPI pathologist Shane Dullahide during field assessments provided an excellent training opportunity in correct disease identification.