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A Technical Guide for Wine Producers
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Economic impact of Eutypa dieback of grapevines
Key words: Eutypa lata, economic impact, grapevine dieback, trunk diseases
Introduction
Eutypa dieback of grapevines is caused by the fungus Eutypa lata. Infection of grapevines by the fungus occurs in winter when the ascospores (sexual spores) of the fungus are released after rain. These ascospores land on pruning wounds where they germinate and penetrate the healthy wood. After infection the disease develops very slowly, with the fungus growing gradually into the wood (approximately 10 cm per annum (Munkvold et al., 1994). As a result of this slow tempo of growth, the first symptoms are only visible several seasons after infection and for this reason Eutypa dieback is seldom observed in plants younger than ten years (Halleen et al., 2001).
Symptoms of infection are especially visible in the first few months of the new growing season. The new shoots are shortened and have a zig-zag appearance. The shoots have short internodes and the young leaves are malformed, yellowish and cup-shaped (Fig. 1). Sometimes the symptoms are visible on one bearer only, spreading to other bearers as the disease develops, until the arm and eventually the entire plant die back (Fig.2). Flower bunches on the shortened shoots appear normal at the beginning of the season, but can dry out and die. If bunches do manage to develop, the berries on the same bunch ripen unevenly, resulting in reduced grape quality (Creaser & Wicks, 2000; Ferreira, 1994; Halleen et al., 2001; Carter, 1988). Cross-sections of affected arms show the characteristic brown, V-shaped lesions caused by infected pruning wounds (Fig. 3).
Crop losses are initially caused by a reduction in the number of bunches per vine (Munkvold et al., 1994), as well as the potential reduction in wine quality (Wicks & Davies, 1999). However, infected vines have a limited life span and must therefore be replanted earlier. As a result Eutypa dieback and other grapevine trunk diseases are directly responsible for the limited life span of Western Cape vineyards.
Economic impact study: Cabernet Sauvignon production in Australia
The occurrence of E. lata in Cabernet Sauvignon in the Eden Valley, Australia, was determined in 1999 (Creaser & Wicks, 2001). Five hundred vines were selected in each of 5 vineyard blocks and the Eutypa symptoms observed on these vines, were ranked in one of four degrees of infection (Fig. 1). Degree 0 was assigned to vines with only healthy shoots; Degree 1 was assigned when shoots had slightly shortened internodes and a mixture of large and small leaves; Degree 2 was assigned when the shoots were further shortened and only had small leaves; Degree 3 referred to drastically shortened shoots with hardly any leaves; and Degree 4 had hardly any shoot development. On average 30.8% of these vines were infected with E. lata. To determine the effect of this infection on crop yield, 100 vines were selected in each of the blocks (representative of all four degrees of infection) out of the original 500, and the yield per vine compared to the yield of healthy vines. From this survey the percentage crop loss resulting from a specific degree of infection could be determined. These results are summarised in Table 1 (Creaser & Wicks, 2001).
Table 1: Annual crop loss caused by Eutypa dieback in Australian Cabernet Sauvignon
Degree
of infection Annual
crop loss Degree
0 Degree
1 Degree
2 Degree
3 Degree
4 Percentage 0 23 46 69 92 Aus$
/ ha
- 2028.39 4056.79 6085.18 8113.57
(Taken from the brochure: Vinevax ä,
Agrimm Technologies, Christchurch, New Zealand)
In a vineyard block where all the vines suffer from degree 1 infection levels, producers can therefore expect an annual crop loss of 23%; an economic loss of Aus$ 2028.39/ha per annum. Similarly a degree 4 infection will cause a 92% production loss per hectare at a cost of Aus$ 8113.57/ha per annum. These figures were calculated on the premise that the degree of infection of all vines in an infected block remains constant, which in actual fact is not the case, since the disease develops on an ongoing basis and becomes more serious in due course of time. Moreover infection levels vary within a block, and not all vines will be affected in the same way, as indicated in Table 1.
Economic impact study: Cabernet Sauvignon production in the Stellenbosch area
Seeing that Eutypa dieback is the most important trunk disease of grapevines in the Western Cape, the above-mentioned situation causes one to contemplate the cost of this disease to Western Cape grapevine producers. In the 2000/2001 season Halleen and collaborators (Halleen et al., 2001) conducted a survey of grapevines with Eutypa-like symptoms in 36 Cabernet Sauvignon blocks (10 years and older) in the greater Stellenbosch area. Degrees of infection ranged from 1 to 4, according to the system used in Australia (Wicks & Davies, 1999; Fig.4). On average 31.7% of these vines were infected with E. lata or related trunk pathogens. Infection levels among blocks ranged from 0% to 98%. That season Cabernet Sauvignon constituted a total area of 3 397.5 ha in the Stellenbosch area, with a total yield of 15 816.4 ton (http://www.sawis.co.za). The total surface planted to Cabernet Sauvignon blocks older than 10 years was only 1 078 ha, however, with an estimated yield of 5 026 t.
To determine the economic impact of this 31.7% E. lata and related trunk pathogen infection in the Stellenbosch area, a conservative assumption was made that infected vines only had a degree 1 infection level. According to the Australian figures, this would have resulted in a crop loss of 23%, provided 100% of the vines in a block suffered from the same degree of infection. For the Stellenbosch area this constituted a 7.3% crop loss, calculated on an average occurrence of Eutypa-like symptoms of 31.7% in the 1 078 ha of Cabernet Sauvignon older than 10 years. This was directly converted to a crop loss of 367 tons, which cost these Stellenbosch Cabernet Sauvignon producers in the 2000/2001 season a loss of income in excess of R 1,7 million (calculated at a Cabernet Sauvignon price of R 4 610 per ton as paid by the co-operatives in the 2000/2001 season). In effect this therefore means a loss of income of R 1 570 / ha. Should the average infection levels in these blocks have been Degree 2, it would have cost producers more than R 3 000 per hectare. Additional losses not calculated in these figures include for example the loss of wine quality.
E. lata and other grapevine trunk pathogens, such as Botryosphaeria and Phomopsis species, are not cultivar specific and similar losses are to be expected for all grape cultivars. An even greater cause for concern is the fact that the life span of vineyards infected with these trunk pathogens is considerably shortened compared to healthy vines. Producers are therefore compelled to re-establish vineyards much earlier at astronomic costs; e.g. between R 50 000 and R 75 000 per hectare to replace Cabernet Sauvignon. Trunk pathogens attack the newly planted young vines through unproteced wounds and the expected life span of these new, young plantings is also shortened. Apart from the crop loss of at least three years' quality grapes during the re-establishment period, the re-establishment costs must therefore also be recovered in fewer seasons.
Preventative disease control
As with the majority of plant diseases "Prevention is better than cure" also applies to grapevine trunk diseases. When symptoms are finally observed, infections are so far advanced that curative control measures are usually ineffective and very expensive. Therefore nurseries and producers are strongly advised to manage Eutypa and other grapevine trunk diseases preventatively throughout. These measures uphold the importance of hygienic nursery practices for the production of "healthy", non-infected vines, planting of certified nursery vines, and vineyard practices that will limit the infection of pruning wounds. The main thrust of these practices involves sanitation measures to reduce inoculum levels and the protection of pruning wounds with biological or chemical wound sealants. Pruning wounds should be protected from the time of vineyard establishment, however, to prevent infections from becoming lodged in the vines, which could later result in Eutypa and dieback. These treatments should cost producers as little as R 50 / ha (excluding labour).
Research
In the past the bulk of the research focussed on Eutypa, but meanwhile it has transpired that Eutypa symptoms in different climatic regions are most likely caused by different pathogen complexes. Researchers should therefore ascertain which specific pathogens and trunk diseases are responsible for dieback in which particular regions. Knowledge of the epidemiology of the specific diseases is of the utmost importance before management practices can be formulated and researched. The effectiveness of different biological and chemical pruning wound treatments and the application of these practices is still not clear, however, and this research should be extended to include the newer diseases.
Knowledge deriving from the above-mentioned research will enable researchers and viticulturists to integrate practices and/or fungicides to recommend tailor-made trunk disease management strategies for individual grape growing regions. Successful management of grapevine trunk diseases will considerably increase the chances of sustainable production of vineyards and by so doing also increase the value, marketability and viability of the product, be it wine or table grapes.
Literature
CARTER, M.V. 1988. Eutypa dieback. In: Compendium of grape diseases. R.C. Pearson & A.C. Goheen (eds). APS Press, Minnesota, USA: p. 32-34.
CREASER, M.V. & WICKS, T. 2000. Eutypa dieback - current status and future directions. The Australian Grapegrower & Winemaker. Annual Technical Issue: p. 82-87.
Creaser, M. & Wicks, T. 2001. Yearly variation in Eutypa dieback symptoms and the relationship to grapevine yield. The Australian and New Zealand Grapegrower and Winemaker 452: p. 50-52.
FERREIRA, J.H.S. 1994. Beheer van tandpyn by wingerd. Wynboer Julie 1994: p. 6-7.
Halleen, F., Volkmann, A., & Fourie, P. 2001. Incidence of Eutypa-like symptoms in Cabernet Sauvignon vineyards in the greater Stellenbosch area. Wynboer 143: p. 12-14.
MUNKVOLD, G.P., GUTHIE, J.A. & MAROIS, J.J. 1994. Reductions in yield and vegetative growth of grapevines due to Eutypa dieback. Phytopathology 85: p. 249-256.
WICKS, T. & DAVIES, K. 1999. The effect of Eutypa on grapevine yield. The Australian Grapegrower & Winemaker. Annual Technical Issue: p. 15-16.
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Jan van Niekerk*(pictured), Paul Fourie* and Francois Halleen**
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