JUNE 2010 GRAPE DAY SEMINAR IMPACT OF BOTRYTIS CINEREA ON VINEYARD RETURNS AND WINE QUALITY

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1 JUNE 2010 GRAPE DAY SEMINAR IMPACT OF BOTRYTIS CINEREA ON VINEYARD RETURNS AND WINE QUALITY Tony Hoksbergen Viticulture Horizons Ltd Over recent years New Zealand has firmly established itself as a producer of internationally acclaimed premium wines. This is spite of, as well as because of, our unique location and terroir I ve heard New Zealand described as a long, narrow, mountainous rock, stuck at the bottom of the South Pacific, in the path of the Roaring Forties. These elements, our location on the globe and our regional diversity (terroir), both contribute to the wonderful flavours our wines develop, but also the unpredictable challenges our climate presents. There is no doubt that Botrytis is the single most challenging and destructive fungal organism that New Zealand grapegrowers and winemakers have to deal with. Many parts of New Zealand face an almost annual battle with this organism and even drier regions such as Marlborough and Canterbury can encounter significant harvest pressure. Even as recently as Vintage 2009, growers faced considerable cost in removing infected bunches from the vine. Those in Marlborough which experienced the horrendous 1995 vintage will be well aware of the consequences of a wet harvest period. The challenge for viticulturists is to produce high quality, disease free fruit, in a commercially and environmentally sustainable manner, while ensuring that our wines distributed into the market have preferably no, or at the very least, minimal pesticide residue, i.e., within international MRL s. As grapes progress through veraison, they become progressively susceptible to Botrytis infection and spread. Part of this is due to the degradation of some of the vines natural defences, the phytoalexins. As Botrytis progresses, it secretes laccase, an enzyme which is suspected of further inactivating these antifungal phenols such as pterostilbene and resveratrol. Skin thickness decreases upon maturity and the digestability of skin pectins by Botrytis pectinolytic enzymes increases. In terms of impact to the industry, both grapegrowers and winemakers are affected. VITICULTURE IMPLICATIONS From a viticultural perspective, revenue implications occur through: A. INPUT COSTS Cost of preventative spraying Canopy management costs such as leaf plucking etc. Cost of removing infected bunches prior to harvest o On the vine o Sorting table B. REVENUE LOSSES Lost revenue through company imposed rot penalties or crop rejection Lost revenue through reduction in crop Let s consider each of these in turn. Page 1

2 A. INPUT COSTS 1. Cost of preventative spraying: Most growers, across our regions (with the possible exception of Central Otago) use conventional Botrytis management techniques. They usually engage in a standard Botrytis control programme which may look something like this: PERIOD PRODUCT OPTIONS COST/HA 5% Capfall (*) Pyrimethanil Products or Soft Products $ % Capfall (*) Pyrimethanil Products or Teldor $165 + Fruit set to bunch closure Only under adverse conditions Dependent on product Pre Bunch Closure Switch $190+ Veraison to Harvest Shirlan or Soft Products $91 + (*) as per NZWG Spray Schedule 09/10 This scenario results in pesticide costs of at least $550 per hectare. If a comprehensive programme involving soft fungicides is included (tricoderma, bacillus, ulocladium, chitosan etc), as well as traditional chemistry, then the dollars spent could rapidly more than double. Added to this is the cost of application (tractor running and staff). To ensure that this expenditure is optimised, the grapegrower needs to ensure that: The sprayer is appropriately calibrated That the sprayer configuration is appropriate to ensure optimal coverage The spray is applied at the optimum time o In terms of vine growth stage o In terms of weather events That the bunches are sufficiently exposed to facilitate good coverage 2. Canopy management costs A well managed canopy which exposes the bunches to air movement and sunlight is one of the most effective Botrytis controls measures available to the grapegrower. This can be achieved by a range of vine management inputs. Depending on the intensity of the treatment and whether each treatment is conducted in isolation or as part of an integrated management approach, the individual input costs could approach: Machine Leaf Pluck per Pass Hand pluck per Pass (two sides) Shoot Thinning $100 - $200 per ha $400 - $600 per ha $350 - $450 per ha The use of sheep for leaf plucking is also finding renewed interest given the cost efficacy. While sheep can provide an excellent leaf pluck, great care must be taken as a significant amount of damage to the canopy (and shoots) can occur in a very short space of time if the sheep are not closely monitored. Great care is also required in terms of the potential for residues in the meat. 3. Cost of removing infected bunches. This activity is very dependent on the extent of infection but could be more than $400/ha. Page 2

3 B. REVENUE LOSSES 1. Rot Penalties: Many companies will have maximum disease levels which they are prepared to tolerate before the crop will be rejected. This level will typically fall in the range of between 7% - 10%. While this may sound low, Botrytis at these levels may significantly compromise the quality of the wine made from these grapes. To put this into context, a 7% rot threshold occurs when: a. 70% of the bunches have 10% rot Or b. 10% of the bunches have 70% rot (Figure 1) Or c. 100% of the bunches have 7% rot (Figure 2) Etc Figure 1: 10% of bunches with 70% severity Figure 2: 100% of bunches with 7% severity 2. Crop Reduction: Under adverse conditions, Botrytis can spread through the bunches very rapidly. Slipskin in particular can move at an alarming rate and I have witnessed on numerous occasions the almost overnight deterioration of grapes where the level of visible infection has moved from relatively low levels to almost 100%. Botrytis will result in crop reduction by two means: A). Human Intervention (physically removing the crop) B). Climatic Effects (dehydration and shrivelling) A). Human Intervention a. The quality of the harvest can be preserved if infected fruit is separated from disease free bunches. This can occur by physically removing infected fruit by hand prior to harvest (negative pick) or alternatively, selectively hand picking the healthy bunches (positive pick) if the infection levels are severe. Both of these processes are very costly. Page 3

4 Gross Revenue Per Hectare b. An additional option exists where all fruit may also be placed across a sorting table where experienced staff can ensure that only the best fruit is selected for the premium blends. This may cost approximately $80 per tonne (plus handpicking costs). B). Climatic Effects a. Crop Reduction Early Season: Severe Botrytis infections early in the season can attack the developing inflorescence resulting in total loss. At more moderate levels, individual flowers can be infected resulting in loss of the flower or alternatively, latent infection in the developing berry which may manifest itself post veraison. b. Crop Reduction - Harvest: As already mentioned, under adverse conditions, Botrytis can spread rapidly through a vineyard block. Berries lose weight rapidly through dehydration or fall from the vine ahead of a mechanical harvester, especially if slipskin Botrytis is present. Accordingly, I have seen crop reductions of over 30% in less than 5 days under extreme conditions. When a potential loss scenario is considered, a significant Botrytis infection event can translate to losses on a 12 t/ha $1500 per tonne of over $5,000 per hectare. $20,000 $18,000 $16,000 $14,000 $12,000 $10,000 $8,000 $6,000 $4,000 $2,000 $- Potential Revenue Impact Due to Botrytis cinerea Under Adverse Conditions - Harvest Time Assumes $1,500 per tonne starting point Days Revenue loss $5,400/ha Gross Revenue WINE IMPLICATIONS WINE QUALITY While Noble rot can be desirable for Botrytised wine styles, for red and white table wines, the negative quality impacts are significant: 1. Musty / mouldy characteristics in the wine loss of freshness Page 4

5 2. Laccase activity in red wines will oxidise anthocyanins, even at low levels which will lead to oxidative browning and colour loss 3. Golden hues, typical of aging occur prematurely in white wines 4. Botrytis can produce esterases that can degrade fruit esters which give many white wines their fruity characters 5. Botrytis can destroy terpenes such as linalool and geraniol, transforming these to less volatile compounds. This is particularly important for varieties such as Gewurztraminer, Riesling and Muscat varieties 6. During infection, Botrytis synthesises polysaccharides inducing increased production of acetic acid and glycerol during fermentation 7. Infection sites can facilitate the development of secondary infections such as sour rot, Aspergillus or Penicillium with consequent impact on wine flavour MANAGEMENT OPTIONS Having discussed the impacts of Botrytis on vineyard management and wine quality, there are a range of options available to growers to minimise Botrytis and thereby optimise returns and wine quality: a. Aim for a balanced vine i. Chose the right terroir ii. Choose the right rootstock iii. Vigour control 1. cover crops 2. Irrigation scheduling Regulated deficit iv. Root pruning v. Fertiliser limit N to what is needed to avoid vigorous canopies, bigger berries and thinner skins vi. Manage crop loading optimum not too heavy or too light crop thin and remove cluster congestion as necessary b. Canopy an open canopy will stimulate airflow and drying while exposure to UV will induce phenolic production including phytoalexins. This can be achieved by: i. Shoot thinning ii. Leaf Plucking iii. Trimming Take care to avoid sunburn on fruit which can increase susceptibility to Botrytis c. Chemical Control i. Chose the right product and apply it at the right time ii. Sprayer calibration apply the right amount of chemical iii. Sprayer configuration ensure the chemical hits the target iv. Control other pests 1. Leafroller caterpillar 2. Birds 3. Powdery Mildew even when not visible, diffuse Powdery Mildew is believed to predispose the berry to Botrytis d. Other measures i. Hygiene remove infected material Page 5

6 1. old rachis are a common source of inoculums and should be removed at pruning 2. Mulch your prunings (the smaller the better faster breakdown) 3. Dead leaves and trash in the canopy, especially in close proximity to the fruit, should be removed. This can be a particular problem under stressed, spur pruned canopies where the cordon and spurs act as an ideal leaf trap. ii. Grow varieties suitable to your region or site don t grow thin skinned, tight bunched varieties (e.g., Riesling) in vigorous soils in humid climates iii. Wine Style sparkling wine grapes are harvested earlier at lower brix and are therefore less susceptible to Botrytis iv. Avoid late season fruit damage (eg., late season leaf plucking can damage berries if not carried out with appropriate care) SUMMARY Viticulturists around New Zealand put a great deal of effort into preventing crop deterioration due to Botrytis. It is expensive to manage and even most costly to mitigate if it becomes established. There are also the obvious wine quality implications which may result in diminished returns for the wine or damage to the reputation of the brand. Experience has shown that by adopting an integrated approach to the management of this disease we can substantially reduce the impact of Botrytis, especially when we compare the challenges we encountered 15 years ago when management techniques were not as well developed. However, significant financial losses can still occur and it is important that we adopt international best practice in our vineyard management routines as well as continue to explore research initiatives which may deliver new solutions for control into the future. Page 6