Non Botrytis Bunch Rot

Transcription

1 Non Botrytis Bunch Rot Questions and answers 21 December 2010 c c wrdc GRAPE AND WINE RESEARCH AND D EVELOPMENT CORPORA TION

2 Identifying the disease Bunch rots on grapevines can be caused by a range of fungi, yeasts and some bacteria, including acetic acid species. The following relates to rots not caused by Botrytis cinerea. For information on botrytis, see the GWRDC s Botrytis: Questions and answers. Q1: What types of non-botrytis rots are there? Non-botrytis rots can be caused by a range of fungi, yeasts and some bacteria. Those that infect berries directly are called primary invaders, while secondary invaders enter the berry through wounds or following infection by a primary invader. A number of rots occur in warm humid areas like the Hunter Valley and they are called sub-tropical fruit rots. Q2: What are the common primary invaders and what do they look like? Alternaria rot The fungus is tan, becoming brown with age. Fluffy gray tufts of fungus develop through cracks in the skin of a berry. Infection can occur through the skin in wet bunches or under very high humidity. Cladosporium rot The fungus causes a black, soft, circular area to develop on the berry. Under high humidity, the conidiophores (that produce spores) and conidia (the spores) of the fungus look velvet-like and are olive green in colour. It is typically a post-harvest disease found on late-harvest fruit after rain. : What are the common secondary invaders and what do they look like? Aspergillus rot or black mould This fungus is common in warm to hot areas. Damaged berries first show tan to brown fungus that develops a dusty mass of brown or black spores. The rot is soft at first, becoming firm and leathery. Aspergillus is frequently associated with sour rot. Penicillium rot or blue mould Penicillium rot or blue mould is easily identified as this fungus produces a mass of dusty blue-green spores. The rot often occurs in berries that have split following rain events or other events that lead to skin damage. Penicillium rot can occur following severe botrytis bunch rot but can occur concurrently with any of the other bunch rotting organisms. The distinctive colour of this rot means it is one of the easiest bunch rots to identify. Q2 Alternaria rot. Photo: Mary Cole. Q2 Aspergillus rot or black mould. Photo: Mary Cole. Cladosporium rot. Photo: Mary Cole. Penicillium rot or blue mould. Photo: Kathy Evans. Non Botrytis Bunch Rot Questions and answers 01

3 Identifying the disease Rhizopus rot Berries develop a soft brown rot that drips juice. High humidity causes cobweb-like black mycelia (the vegetative part of a fungus) to develop. Dark sporangia (the structure that produces and contains the spores) appear in skin cracks or wounds in the berry skin. The fungus can spread to other berries in the cluster. Along with Aspergillus, Rhizopus is often associated with sour rot. Sour rot Various fungi, yeasts, acetic acid bacteria and vinegar fly larvae, combined with other organisms, can cause sour rot. Juice from infected berries smells like vinegar. The rot can spread in the cluster. Q4: What are the common subtropical fruit rots and what do they look like? Ripe rot or Colletotrichum rot Berries develop round, reddish skin spots. These grow over the whole berry, which becomes covered with salmon-coloured conidia (spores). The berries then shrivel and can drop. In subtropical environments, ripe rot frequently occurs late in the season following an earlier bitter rot infection (see below). Unlike many of the other non-botrytis bunch rots, ripe rot seems to occur more frequently in open canopies, particularly in association with sunburn. Bitter rot or Greeneria rot Bitter rot is frequently seen as a series of concentric rings of black sporulation around the circumference of the berry. White grapes develop a brownish colour, black grapes have a rough appearance. Berries shrivel and can drop or remain attached to the bunch. Rhizopus rot. Photo: Mary Cole. Sour rot. Photo: Turner Sutton. Non Botrytis Bunch Rot Questions and answers Q4 Ripe rot or Colletotrichum rot. Photo: Tony Somers. Q4 Bitter rot or Greeneria rot. Photo: Tony Somers. 02

4 The diseases Q5: How do I get non-botrytis rots in my vineyard? Most of the fruit rotting diseases are caused by fungi. Fungi produce many spores, which can be dispersed by wind, dust and rain. Insects can carry them on feet or mouthparts. The diseases can carry over from the previous season on mummified berries, dead wood, bark, canes and spurs, vineyard debris and decaying vegetation or in the soil. Many of the fungi associated with nonbotrytis bunch rots also attack other host plants, which can in turn be sources of infection. For instance, ripe rot isolates from grapes are able to infect olives, strawberries and blueberries, and vice versa. There is the possibility that Colletotrichum acutatum could spread from nearby non-grape host plants into vineyards. Q6: What conditions favour the development of these diseases? Like botrytis, other berry rots are favoured by wet weather and high relative humidity during the growing season. Higher rainfall increases the risk and amount of these diseases. A sequence of favourable seasons can increase the incidence and severity of these diseases. Some grapevine varieties are more likely to be affected than others, particularly if they have dense clusters and vigorous canopies. Any damage to the berry skin (e.g. insect damage, hail, berry splitting after rainfall) will lead to a greater incidence of all bunch rots, including Botrytis cinerea. Q5 Slide: Julie Miranda Longland Q5 Slide: Katherine Whitten Buxton Non Botrytis Bunch Rot Questions and answers 03

5 Managing the diseases Q7: How can I predict which rot I will have this season? Q8: What differences will regional climates have on the rots observed? It is difficult to predict which organism will predominate in a given season. In a season that is exceptionally wet, the inoculum pressure in the vineyard will be high. Under these circumstances the likely success of any bunch rot management practices is difficult to predict. Management of non-botrytis bunch rots, and in particular ripe rot and bitter rot, continues to be a challenge in wet warm seasons. The bunch rot pathogen profile varies from season to season, largely due to climatic influences but also in response to management practices. Regional climate will also influence the types of fruit rots found. The Riverina, for example, is renowned for Noble rot or botrytis. As mentioned above, the sub tropical rots (bitter rot and ripe rot) are generally not found in cooler regions. Q7 Environmental factors that might influence non-botrytis bunch rot development include water availability, heat and light. The infection of a given grape berry might also be influenced by biological factors, such as the microflora living on the berry. Two or more bunch rot pathogens frequently occur together on a bunch and even a single berry. Q9: Can pruning practices reduce some non-botrytis rots? As a general rule, the more old diseased wood and debris that is retained in the canopy, the higher the risk of diseases such as ripe rot, bitter rot and sour rot. Poor surface drainage in the vineyard can create hot spots for fruit rot due to high humidity. Photo: Chris Haywood. Q9 Q7 Slide: Turner Sutton NS= Not significant Non Botrytis Bunch Rot Questions and answers 04

6 Managing the diseases Acknowledgements Q10: What viticultural practices will help reduce non-botrytis rots? Most of the fungicides registered for botrytis control are ineffective against both ripe rot and bitter rot. Also, recent research suggests that open canopies (used for botrytis management) combined with heat stress may predispose fruit to a greater incidence of ripe rot. Viticultural practices that may help include: improving air circulation and light penetration through weed control and de-suckering well-spaced shoot positioning or removing shoots for uniform leaf development, and choosing your row direction to taking advantage of the prevailing wind. Good air circulation and light penetration will dry the canopy faster and reduce disease incidence. Q11: What is the impact on wine quality of non-botrytis rots? Generally, all the fungi associated with grape bunch rots lead to mouldy, musty off flavours in finished wine, although the specific effects of individual organisms are not yet understood. It is likely that many of the fungi involved with bunch rots produce the oxidative enzyme laccase, which destroys red pigmentation and can cause oxidative spoilage of wine. This information was compiled by Tony Somers and Professor Chris Steel, drawing on the work of the National Wine and Grape Industry Centre (NWGIC) Winegrowing Futures Program Non- Botrytis Bunch Rots research work. Valuable contributions were received from Mark Krstic and Kate Harvey (GWRDC), Liz Riley (VitiBit Pty Ltd), Scott Matthew (Sygenta), Dr Kathy Evans (TIAR), Dr Bob Emmett (DPI Victoria) and Duncan Farquhar (NWGIC). References M. Meunier and C.C. Steel (2009) Effect of Colletotrichum acutatum on wine quality, Australian Journal of Grape and Wine Research 15, C.C. Steel, L. Greer and C. Haywood (2008) The Australian & New Zealand Grapegrower & Winemaker, September 2008, issue 536, C.C. Steel (2004) Fruit rot control in Hunter Vineyards. Providing growers with tools to stop the rot. GWRDC Project RT 02/39 4 C.C, Steel (2007) Management of non-botrytis bunch rots. GWRDC Project CSU 03/01 A. Somers (2003) Control of bitter rot or ripe rot of grapes caused by Colletotrichum spp. GWRDC Project RT 01/14 R.C. Pearson and A.C. Goheen (Ed) (1994) Compendium of Grape Diseases. The American Phytopathological Society. M. Cole and S. Whitmore. Identification of Botrytis and other bunch rots. T.B. Sutton (2009) Non-botrytis bunch rots in the southeastern US and their management. Hunter Valley Wine Industry Association Vineyard Health Workshop. ccwrdc GRAPE AND WINE RESEARCH AND DEVELOPMENT CORPORATION Non Botrytis Bunch Rot Questions and answers 05