In this section:
Eutypa dieback symptoms
Yearly Variation in Eutypa Dieback Symptoms and the Relationship to Grapevine Yield
Mette Creaser A,B and Trevor Wicks A,B
A Cooperative Research Centre for Viticulture, PO Box 154, Glen Osmond SA 5064
B South Australian Research and Development Institute, GPO Box 397, Adelaide SA 5001
Introduction
Eutypa dieback has been recognised as a major fungal disease of grapevines in Australia for over 60 years (Wicks, 1975). An insidious disease, Eutypa dieback contributes to the decline of vineyards by reducing growth and yield, and eventually killing vines.
Eutypa dieback is most obvious in early spring when infected vines show stunted shoots with shortened internodes and small leaves that are usually pale in colour, cupped and tattered around the margins. Bunches on affected shoots appear normal early in the season but after flowering they often shrivel and die. If bunches are retained through to harvest they may be considerably smaller than bunches on unaffected shoots. These symptoms are often localised to individual spurs, close to the site of initial Eutypa infection. However, in succeeding seasons, the disease spreads to adjacent parts of the vine and eventually kills affected spurs.
Studies have shown that as disease severity increases yield decreases (Munkvold et al., 1994; Wicks & Davies, 1999). However, neither study monitored the same vines for more than one year, with the result that no account was taken of yearly variation in symptom expression. Anecdotal evidence suggests that symptoms of Eutypa dieback vary from year to year. Our aim was to evaluate the variation in Eutypa dieback symptoms and its relationship to grapevine yield.
Material and Methods
In the spring of 1999 (15 December), approximately 125 own-rooted Shiraz vines in each of two vineyards in the Coonawarra district of South Australia were selected so that about 25 vines fell into each of five disease severity categories. Disease severity was rated on a 0-4 scale of shoot stunting (Figure 1.), where 0 = symptomless and 4 = severely stunted shoots (Wicks & Davies, 1999). Vines were harvested by hand and the total yield per vine recorded. Vineyard One was harvested on 7 March 2000 and Vineyard Two on 14 March 2000.
In the spring of 2000 (31 October), the same vines were re-assessed for disease severity. Yield data were collected at harvest from Vineyard One on 21 March 2001 and from Vineyard Two on 20 March 2001.
Both vineyards were established in 1968 on a standard T system and are usually machine pruned and harvested. Vineyard One is drip irrigated whereas Vineyard Two has overhead sprinklers.
Results
Variation in Symptom Expression
In both vineyards, symptoms of Eutypa dieback were less severe in many vines in the spring of 2000 than in the spring of 1999 (Fig. 2.). For instance, in Vineyard One, 25 vines were free of foliar symptoms in 1999 increasing to 59 vines in 2000.
The Relationship to Yield
Regression analyses demonstrated significant linear relationships between disease severity and yield per vine in both vineyards and in both years (Fig 3.). As in previous studies, the yield per vine decreased as disease severity increased.
To facilitate comparisons between vineyards and years of assessment, data from each vineyard were adjusted to a percentage value based on the average yield of a symptomless vine in that vineyard and in that year (Munkvold et al., 1994). When the data were re-analysed, we found that there was no significant difference between vineyards or years of assessment (Fig 4.) and that the relationship between yield (Y) and disease severity (x) could be described by a single line: Y(% of symptomless) = 101.7 - 17.1x.
Yield lost to the disease
Using this equation, we calculated that the yield lost to Eutypa dieback in each vineyard was:
|
|
2000 |
2001 |
|---|---|---|
|
Vineyard One |
32.3% |
21.4% |
|
Vineyard Two |
31.9% |
14.9% |
where x = the mean disease rating for each vineyard in each year.
Yield lost to the disease was significantly greater in 2000 compared with 2001 in both vineyards. However, there was no significant difference in the yield lost between vineyards in either year.
Discussion
We have demonstrated that the severity of foliar symptoms of Eutypa dieback varies from year to year. However, the relationship between disease severity and yield is constant and unaffected by the yearly variation in symptom expression. This suggests that it may be possible to predict the yield lost to Eutypa dieback by assessing foliar symptoms in the spring prior to harvest.
This study has shown that Eutypa dieback is responsible for significant yield reductions in premium Shiraz vineyards in the Coonawarra. Losses to the disease ranged from 15% to 32% in the two vineyards under observation, with yield loss more severe in 2000 than in 2001.
Of the 240 vines selected for inclusion in the study, most vines showed symptoms of Eutypa dieback, including dead spurs and cankers. For this reason, vines showing no foliar symptoms of the disease were referred to as “symptomless” rather than as “healthy”. The distinction between symptomless and healthy (or uninfected vines) vines is particularly important as we have shown that symptoms of Eutypa dieback can vary from year to year and infected vines may not exhibit foliar symptoms in some years. For instance, of 90 vines showing foliar symptoms in 1999, 38 showed no symptoms in 2000. This suggests that to determine the number of infected vines in a vineyard, vines must be monitored over several years.
Further work is now required to determine whether we can use the information collected to predict yield loss in subsequent years. Data will be collected from both vineyards over the next few years to try to establish the underlying cause of yearly variation in Eutypa symptom expression. Acknowledgements
We wish to thank the growers involved in this work, Tim Kidman of Clytha and Peter Broadbent of Orlando Wyndham, and gratefully acknowledge the CRC for Viticulture and the GWRDC for their support.
References
Munkvold, G.P., Duthie, J.A., and Marois, J.J. (1994). Reductions in yield and vegetative growth of grapevines due to Eutypa dieback. Phytopathology 84:186-192.
Wicks, T. (1975). The dying arm disorder of vines in South Australia. Agricultural Record 2:14-20.
Wicks, T. and Davies, K. (1999). The effect of Eutypa on grapevine yield. The Australian Grapegrower and Winemaker Annual Technical Issue 1999.
Figures
Figure 1. The 0 to 4 scale used to measure the degree of shoot stunting in Eutypa dieback affected vines.
Spring 1999 Spring 2000
Figure 2. Number of vines showing foliar symptoms of Eutypa dieback in each Coonawarra vineyard in the spring of 1999 and 2000.
Vineyard One Vineyard Two
Figure 3. Relationship between symptom expression and yield per vine in 1999/2000 and 2000/2001; where Y1=yield in Vineyard One, Y2=yield in Vineyard Two, and x= Disease Severity
Vineyard One Vineyard Two
Figure 4. Relationship between symptom expression and yield per vine when data are expressed as a percentage of the estimates for symptomless vines for both 1999/2000 and 2000/2001; where Y=yield and x= Disease Severity.
