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Incidence of Eutypa-like symptoms in Cabernet Sauvignon vineyards in the greater Stellenbosch area
The fungus Eutypa lata is the causal agent of eutypiose or Eutypa dieback (tandpyn) of grapevines. Infection occurs when ascospores (sexual spores) of the fungus enter fresh pruning wounds in mature wood. The ascospores germinate and grow into the healthy wood below the wound. This fungal growth, however, is slow (± 10cm/year) and it may take two or three seasons before symptoms occur. This might explain why Eutypa dieback is rarely seen in plants younger than ten years. The disease has a severe influence on the productive lifespan of a vineyard and this is not only reflected in the loss of yield, but also in the cost of reworking, removing and replanting of such a vineyard.
Eutypa lata is commonly associated with symptoms like stunted, zig-zag shoot growth and dieback of arms or even entire vines. Although symptom expression differs considerably between cultivars, leaves on affected shoots are small and usually yellow, cupped, tattered, speckled, and often dead around the margins (Carter, 1988). Flower clusters on stunted shoots are normal, but shrivel and die on severely affected shoots. Bunches that appear normal at the beginning of the season may also shrivel and die (Creaser & Wicks, 2000). Yield reduction is primarily due to a diminished number of clusters per vine (Munkvold et al, 1994). Reduced wine quality may also occur due to uneven berry maturity from infected vines (Wicks & Davies, 1999).
Other diseases that could elicit similar dieback symptoms are Phomopsis viticola, causing dead-arm (Moller & Kasimatis, 1981), and Botryosphaeria species, causing black dead-arm (Lehoczky, 1988). However, these pathogens do not elicit the typical shoot symptoms as observed in Eutypa-infected vines (Ferreira, 1988). The foliar symptoms are not the direct result of the fungus, but rather that of a toxin, eutypine, produced by the fungus and transported through vascular tissue to the affected shoots (Tey-Rulh et al, 1991).
In South African vineyards the general incidence of this disease is not known. Consequently, a study was undertaken to investigate the incidence of Eutypa-like symptoms in Cabernet Sauvignon vineyards in the greater Stellenbosch area.
Materials and Methods
A survey was conducted in 36 randomly selected Cabernet Sauvignon vineyards, situated on 36 different farms in the greater Stellenbosch area. These areas included Jonkershoek (one farm), Simonsberg (11 farms), Helderberg (five farms), Stellenboschkloof (seven farms), Muldersvlei (one farm) and Bottelary (two farms). Vineyard age ranged from 10 to 22 years. A hundred vines per vineyard were inspected for Eutypa-like symptoms.
Results and Discussion
The average level of infection was 31.7%, with the highest level recorded in a 22 year old vineyard (Table 1). In this vineyard 98% of the vines showed Eutypa-like symptoms. The lowest level of infection was found in one 12 year old vineyard, which was the only vineyard where no Eutypa-like symptoms were observed. Results show that the incidence of Eutypa-like symptoms increased with age of the vineyard (Table 2). Factors other than age, such as pruning method, pruning time and the use of wound sealing agents also play a role in the susceptibility of vines to Eutypa infection (Munkvold & Marois, 1995). However, from the survey it was evident that producers are extremely reluctant to apply wound sealing agents or manual fungicide applications. Due to time constraints, many producers are also pressured to prune during rainy conditions. Since Eutypa ascospores are released during the latter conditions, pruning wounds are extremely susceptible to infection during these periods.
This preliminary survey of the incidence of Eutypa-like symptoms in Cabernet Sauvignon vineyards clearly illustrates the economic importance of this disease in South Africa. A study is currently in progress at ARC Infruitec-Nietvoorbij to investigate the effectiveness of various fungicides, biological control agents or combinations of fungicides and biological control agents for pruning wound protection.
For further information contact Francois Halleen at telephone (021) 809 3040, fax (021) 809 3002 or e-mail: francois@nietvoor.agric.za.
References
Carter, M V, 1988. Eutypa dieback. In: Compendium of grape diseases. R C Pearson and A C Coheen (eds). APS Press, Minnesota, USA, pp 32 - 34.
Creaser, M & Wicks, T, 2000. Eutypa dieback - current status and future directions. The Australian Grapegrower & Winemaker. Annual Technical Issue, pp 82 - 87.
Ferreira, J H S, 1988. Dieback of grapevines in South Africa. PhD thesis, University of the Western Cape, Private Bag X117, 7530 Bellville.
Lehoczky, J, 1988. Black dead arm. In: Compendium of grape diseases. R C Pearson and A C Coheen (eds). APS Press, Minnesota, USA, pp 35.
Moller, W J & Kasimatis, A N, 1981. Further evidence that Eutypa armaniacae - not Phomopsis viticola - incites dead arm symptoms on grape. Plant Disease 65: 429 - 431.
Munkvold, G P, Duthie, J A & Marois, J J, 1994. Reductions in yield and vegetative growth of grapevines due to Eutypa dieback. Phytopathology 84: 186 - 192.
Munkvold, G P & Marois, J J, 1995. Factors associated with variation in susceptibility of grapevine pruning wounds to infection by Eutypa lata. Phytopathology 85: 249 - 256.
Tey-Rulh, P, Philippe, I, Renaud, J M, Tsoupras, G, De Angelis, P, Roustan, J P, Fallot, J & Tabacchi, R, 1991. Eutypine, a phytotoxin produced by Eutypa lata, the causal agent of dying-arm disease of grapevine. Phytochemistry 30: 471 - 473.
Wicks, T & Davies, K, 1999. The effect of Eutypa on grapevine yield. The Australian Grapegrower & Winemaker. Annual Technical Issue, pp 15 - 16.
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