PW214-2 – Vine Pathology

1. PW214-2 – Vine Pathology THE Effects of Pest Management on Wine Quality Kristina Studzinski FdSc Wine Production 2012/13

2. Contents • Introduction • Botrytis • Powdery mildew • Grapevine viruses, bunch stem necrosis and downy mildew • Birds, nematodes and insects • Fungicides and pesticides • Elicitors • Summary and conclusions

3. Introduction It is stating the obvious that healthy grapevine development ensures the quality of grapes produced by the vine. Also that the quality of a wine depends on the quality of grapes used. Agents that attack berries directly such as the major fungal pathogens impact on fruit quality (Jackson, 2008). Additionally, the use of fungicides and pesticides can have an impact on wine quality due to residues that might be left on berry skins (Margalit, 2004). Vineyard pests and diseases have been shown to affect wine quality in a variety of ways. This may be because of the obvious effects of disease such as berry shrivelling, decay and tissue destruction but it may also be because of more subtle effects such as decreased photosynthesis or reduced root growth (Jackson, 2008). The winemaking process itself may be affected by the by-products of pathogens and their effects on juice constituents such as total soluble solids, titratable acidity and pH (Cabaleiro, Segura and Garcia-Berrios, 1999, Jackson, 2008).

4. Botrytis • Of fruit infecting fungi, the negative effects of Botrytis cinereaon wine quality are well known (Ribéreau-Gayon, Ribéreau-Gayon and Seguin, 1980 ,Jackson, 2008). Botrytis cinereaproduces a very destructive grey rot which has the following effects on wine making and wine quality: • Off flavours (Mushroom, earthy) may be generated by fungi producing mycotoxins and secondary invaders such as Penicillin and Aspergillus(Jackson, 2008), • High levels of fixed and volatile acidity due to early invasion of infected fruit by acetic acid bacteria (Jackson, 2008), • Difficulty in red wine making due to high levels of laccase, which oxidises anthocyanins and generates unacceptable phenol flavours (Jackson, 2008), • Increased polysaccharide levels resulting in clarification problems (Girbau et al., 2004, Jackson, 2008), • Higher levels of SO2 additions due to higher SO2 combing ability of the wine (Ribéreau-Gayon, Ribéreau-Gayon and Seguin, 1980), • Reduced Nitrogen and sugar levels that lead to fermentation difficulties (Jackson, 2008) •  In relation to sparkling wine making, Botrytis cinereaexcretes an aspartic acid protease that is capable of degrading the important proteins that influence effervescence (Hong et al, 2011). • But under the right conditions Botrytis cinereainfection produces noble rot resulting in sweet wines of outstanding quality (Jackson, 2008). Climatic conditions are critical so that as the grapes ripen the weather must be moist enough for the fungus to grow and infect the healthy grapes. This must be followed by drier weather to allow evaporation of the water from the infected fruit and a temperature that allows water loss but not be so high as to retard the growth of Botrytis (Ribéreau-Gayon, Ribéreau-Gayon and Seguin, 1980). Climatic conditions in the UK do not favour noble rot but it is possible to produce a quality Botrytis wine under controlled conditions at a high cost (Nelson and Amerine, 1956)

5. Powdery Mildew • Powdery mildew (Uncinulanecator) has a major negative effect on wine quality. This is due to the direct effects of infection and indirect effects such as changes in microbial populations, total soluble solids and fermentation rates (Stummer et al. 2003). • Studies have shown that powdery mildew has a variety of different effects on wine quality some of which differ between cultivars. In summary, powdery mildew: • Produces a ‘bitter to distinct off taste’ in wine made from Thompson Seedless, Carignane and Ribier but doesn’t affect fermentation rate (Ough and Berg, 1979), • Increases titratable acidity, total phenolics, hydroxycinnamates and flavanoids in Chardonnay juice and wine made from Chardonnay (Stummer et al., 2003), • Lowers total soluble solids in Chardonnay grapes with infection greater than 30% which affects fermentation rates (Stummer et al., 2003), • Lowers total soluble solids in Cabernet Sauvignon bunches and total phenolics and spectral colour values (Stummer et al., 2003), • Produces wine made from Chardonnay that has higher ‘oily’ and ‘viscosity’ attributes (Stummer et al., 2003), • Increases levels of protein haze (Girbau et al., 2004), • Affected grapes may take twice as long to complete fermentation (Ewart et al., 1993 cited in Jackson, 2008). • Data on disease incidence and severity is lacking in some published reports as is the effect on wine quality by quantified levels of powdery mildew infection (Stummer et al., 2003). • It has been found that even very low levels of infection (1-5%) can be detrimental to wine sensory characteristics (Stummer et al., 2003).

6. Grapevine viruses, bunch stem necrosis and downy mildew • Grapevine viruses can both directly and indirectly affect berries (Jackson, 2008). Viral infections induce changes in plant physiological processes such as: photosynthesis, respiration, enzymatic activity, nutrient transport, hormone balance and mineral nutrition which can impact on the quality of fruit (Cabaleiro, Segura and Garcia-Berrios, 1999). Leafroll virus has been shown to: • increase titratable acidity which results in wines with lower pH and poor colour (Cabaleiro, Segura and Garcia-Berrios, 1999, Jackson, 2008), • reduce the sugar content of Albarino grapes (Cabaleiro, Segura and Garcia-Berrios, 1999). Sugar accumulation in the berries is decreased due to the suppression of transport from the leaves (Jackson, 2008). • Studies that have looked at the effects of leafroll and fanleaf virus on grape juice composition have concluded that there are considerably different effects dependent on cultivar (Credi and Babini, 1997, Cabaleiro, Segura and Garcia-Berrios, 1999). • Stem Pitting Virus may advance fruit maturity in terms of titratable acidity and pH but has no apparent negative impact on berry composition (Reynolds, Lanterman and Wardle, 1997). • Bunch stem necrosis causes grapes to shrivel and fruit to fall around and after veraison (Jackson, 2008). Wines produced from affected vines have been shown to be imbalanced, high in acidity, low in ethanol and higher alcohols and esters (Ureta et al., 1982 cited in Jackson, 2008). • Little is known about the effect of downy mildew (Plasmoparaviticola) on wine quality (Jackson, 2008). Mature berries are resistant to infection but they may be killed if berry or bunch stems get infected (Nicholas, Magarey and Wachtel, 1994).

7. Birds, Nematodes and insects • Insects and other pests such as birds can damage fruit directly and they can create lesions that assist invading microbes (Jackson, 2008). Weak vines may suffer an increased incidence of bird damage (Schroth et al., 1988 cited in Jackson, 2008). • The only fruit parameter affected by nematodes has been found to be juice pH with lower values found in vines infected by ring nematodes compared to non-infested vines (Schreiner, Zasada and Pinkerton, 2012). But nematodes can spread viruses that affect fruit quality. • The Asian lady beetle, Harmoniaaxyridis, common in some parts of the US releases a yellow smelly fluid that may be detectable in wine at certain thresholds (Galvan et al., 2007). There are no insects in the UK that have such a direct effect on wine quality.

8. Fungicides and pesticides • Most of the chemicals used in pest management end up in the must as they leave residues on the grapes that remain at harvest time (Margalit, 2004). This was the conclusion of a study by Cabras et al., in 1987 (Cabras et al., 1987 cited in Margalit, 2004). The exact quantity of the residue will depend on factors such as: • The number of applications, • The concentration of the chemical used, • Weather conditions, • The last application before harvest and the degradation rate of the product (Margalit, 2004). • Most of the residues disappear either by yeast settling or by fining. Some residues may inhibit fermentation (Margalit, 2004). Fining with activated carbon has been found to be particularly effective in removing pesticides from wine (Ruediger et al., 2004). • The copper in Bordeaux mixture that is used against downy mildew can compromise wine quality and reduce the concentration of varietal compounds (Jackson, 2008). Prolonged skin contact can reduce this effect (Hatzidimitriou et al., 1996 cited in Jackson, 2008). • Sulphur pesticides that are used to stop powdery mildew may leave traces of elemental sulphur that lead to hydrogen sulphide formation and off aromas in wine (Margalit, 2004). • Fungicides and pesticides may cause direct damage to the vine and more subtle changes such as reduced sugar accumulation in berries (Hatzidimitriou et al., 1996 cited in Jackson, 2008).

9. Elicitors • Elicitors are compounds that trigger defence mechanisms in plants and are used as alternatives to pesticides. One of the defensive chemicals produced by plants in response to pathogens is salicylic acid which is a close relative of aspirin and which causes the plant to produce pathogenesis-related proteins some of which are enzymes that break down the cell walls of pathogens (Purves et al., 2004). • In a recent study, it was shown that two compounds that are used as elicitors to increase resistance to Botrytis attack, benzothiadiazole (BTH) and methyl jasmonate (MeJ), contribute positively to the aroma and taste of wine and to the colour (Gomez-Plaza et al., 2012). The application of BTH and MeJ increased terpenes and norisoprenoids in wine made from Monastrell grapes which is a non-aromatic variety. Terpenes and norisoprenoids are responsible for floral and citric aromas (Gomez-Plaza et al., 2012). • Another study has shown that the application of BTH and MeJ results in an increase in phenolic composition of berries and wines made from those berries (Ruiz-Garcia et al., 2012). • A new chitosan formulation that elicits plant defence against a variety of pathogens including powdery mildew infection improved total polyphenol content and antioxidant activity in grapes and wine (Iriti et al., 2011). • The use of plant defence inducers deserves particular attention because of their ability to improve some quality traits in the plant (Iriti et al., 2011).

10. Summary and Conclusions It’s not all bad news! • The fungal pathogens, Botrytis cinereaand Uncinulanecator (powdery mildew), impact most on wine quality. • Viruses do damage to the grapevine’s physiology which can directly and indirectly impact on wine quality. • The effects of pesticides and fungicides on wine quality can be ameliorated by controlled and judicious application. • The winemaker can rectify some of the negative effects caused by pesticide residues by, for example, fining and filtration. • Insects, nematodes and birds generally have little impact on wine quality but may aid the spread of disease. • Elicitors may not only prevent disease but bring positive effects on wine quality. • Different cultivars may vary in their responses to diseases. • In making practical decisions on disease control, it is important to understand the effects of disease, pesticides and fungicides on wine quality. • It might still be possible to make wine from fruit from diseased vines so it’s not all bad news!

11. References References • Cabaleiro, C., Segura, A., and Carcia-Berrios, J.J., 1999. Effects of Grapevine Leafroll-Associated Virus 3 on the Physiology and Must of Vitisvinifera L. Cv. Albarino Following Contamination in the Field, The American Journal of Enology and Viticulture 50, pp 40 - 44. • Credi R., and Babini, A., R. ,1997. Effects of Virus and Virus-Like Infections on Growth, Yield and Fruit Quality of Albana and TrebbianoRomagnolo Grapevines, The American Journal of Enology and Viticulture 48, pp7 -12. • Galvan, T., L., Burkness, E.,C., Vickers, Z., Stenberg, A., Mansfield, A.,K., and Hutchison, W.,D., 2007. Sensory-Based Action Threshold for Multicolored Asian Beetle-Related taint in Winegraps,The American Journal of Enology and Viticulture 58:4, pp 518 - 522. • Girbau, T., Stummer, B., E., Pocock, K., F., Baldcock, G.,A., Scott, E., S., and Waters, E., J., 2004. The effect of Uncinulanecator(powdery mildew) and Botrytis cinereainfection of grapes on the levels of haze-forming pathogenesis-related proteins in grape juice and wine, Australian Journal of Grape and Wine Research 10, pp 125 – 133. • Gomez-Plaza, E., Mesre-Ortuno, L., Ruiz-Garcia, Y., Fernandez-Fernandez, J.,I., and Lopez-Roca, M., 2012. Effect of Benzothiadiazole and Methyl Jasmonate on the Volatile Compound Composition of VitisVinifera L., Monastrell Grapes and Wine,The American Journal of Enology and Viticulture 63:3, , pp 394 - 401. • Hong, Y-S., Cilindra, C., Liger-Belair, G., Jeandet, P., Hertkorn, N., and Schmitt-Kopplin, P., 2011. Metabolic Influence of Botrytis cinerea infection in Champagne Base, Journal of Agricultural Food Chemistry, 59 (13), pp 7237 -7245. • Iriti , M., Vitalini, S., Tommaso, G., D., D’Amico, S., Borgo, M., and Faoro, F., 2011. New chitosan formulation prevents grapevine powdery mildew infection and improves polyphenol content and free radical scavenging activity of grape and wine, Australian Journal of Grape and Wine Research, 17 pp 263-269. • Jackson, R., S., 2008. Wine Science: Principles and Applications, 3rd Edition, Elseiver Inc., Canada, pp 183 – 184. • Margalit, Y., 2004. Concepts in Wine Chemistry, 2nd Edition, The Wine Appreciation Guild, US, pp 337, 368 – 369. • Nelson, K., E., and Amerine, M., A., 1956. Use of Botrytis Cinerea for the Production of Sweet Table Wines, The American Journal of Enology and Viticulture 9, pp 131 -136. • Nicholas, P., Magarey, P., and Wachtel, M., 1994.Grape Production Series Number 1- Diseases and Pests, Winetitles, p 6. • Ough, C.S., and Berg, H.W., 1979. Research Note Powdery Mildew Sensory Effect on Wine, The American Journal of Enology and Viticulture 30, p 321. • Purves, W., K., Sadava, D., Orians, G., H., and Heller, H., C., 2004. Life: The Science of Biology, 7th Edition, Sinauer Associates Inc., US, pp 766 – 768. • Reynolds, A.,G., Lanterman, W.S., and Wardle, D.,A., 1997. Yield and Berry Composition of Five Vitis Cultivars as Affected by Rupestris Stem Pitting Virus, The American Journal of Enology and Viticulture 48, pp 449 -458. • Ribéreau-Gayon, J., Ribéreau-Gayon, P., and Seguin, G., 1980. Botrytis ciinerea in Enology. In RColey-Smith, J.R., Verhoeff, K., Jarvies, W.R. ed.,1980. The Biology of Botrytis, Academic Press, UK pp 258 -259. • Ruediger , G., A., Pardon, K., H., Sas, A., N., Godden, P., W., and Pollintz, A., P., 2004. Removal of pesticides from red and white wine by the use of fining and filter agents, Australian Journal of Grape and Wine Research 10, pp 8-16. • Ruiz-Garcia, Y., I., Romero-Cascalera, R., Gill-Madox, J., I., Fernandez-Fernandez, J.,M., Lopez-Rosca and Gomez-Plaza, E., 2012. Improving grape phenolic content and wine chromatic charactersitics through the use of two different eleicitors: Methyl jasmonatevsBenzothiadizole. Journal of Agricultural Food Chemistry 60, pp 1283 – 1299. • Schreiner, R.,P., Zasada, I., A., and Pinkerton, J.,N., 2012, Consequences of Mesocriconemaxenoplax Parasitism on Pinot noir Grapevines Grafted in Rootstocks of Varying Susceptibility, The American Journal of Enology and Viticulture 63:2, pp 251 -261. • Stummer, B., E., Francis, I., L., Markides, A.,J., and Scott, E., S., 2003. The effect of powdery mildew infection of grape berries on juice and wine composition and on sensory properties of Chardonnay wines, Australian Journal of Grape and Wine Research 9, pp 28-39. (Word count - 1777)