22 February 2023 

This season, conditions have been conducive to the development of fungal diseases. As harvest approaches, grapegrowers and winemakers across the country are under pressure to meet quality targets by managing the level of disease-affected fruit entering the winery. This eBulletin provides a reminder of the resources that are available for winemakers and grapegrowers to meet wine quality targets in a fair, equitable and mutually beneficial manner.

Disease assessment
Information about monitoring for key grapevine pest and diseases found in Australia can be found on the pests, diseases and viruses page of the AWRI website. Grape Assess is a digital monitoring tool developed by the University of Adelaide, with funding from Wine Australia, that uses visual techniques to assess diseases and disorders on grapes. Grape Assess can be downloaded for free from the Android and Apple app stores.

The Code of Conduct for Winegrape Purchases
The Code of Conduct for Winegrape Purchases was developed for the Australian wine sector by Australian Grape & Wine (AGW) and its Code Management Committee (a committee with equal representation of winemakers and grapegrowers). The Code sets minimum standards relating to grape purchasing, including mechanisms for determining price; quality assessment for the purpose of affecting price; and payment terms.

The Code is a non-prescribed voluntary industry code. Winemakers who elect to become signatories are governed by this Code in their commercial dealings with growers. Where the Code is incorporated into a contract by reference, it has contractual force. There are currently 72 signatories of the Code, representing 60-70% of the Australian winegrape crush. A list of signatories can be found here.

Grapegrowers and winemakers are encouraged to familiarise themselves with the Code to ensure they know their obligations and rights.

Fruit condition assessment
Key points from The Code related to fruit condition assessment are summarised below.

• A grower should always have the right to be present during a vineyard inspection and this should be encouraged.
• When assessing grapes against MP&C standards (mature, pure and in good condition) or grading them or otherwise making assessments of grapes, signatories must:
  1. (1) avoid the use of subjective measures to determine price, in circumstances where there are credible objective measures readily available to measure the same or similar characteristics;
  2. (2) where available, use Industry Endorsed Standard Procedures; and (3) clearly document their methodology and results, and retain that documentation.
• Notification of possible downgrading, penalties or rejection will be in accordance with timeframes laid out in the Code (for Code signatories) and in any case as early as possible with consideration to the fact that the grower may wish to seek alternative arrangements to prevent further loss. Furthermore, identifying problems as early as possible allows the grower the opportunity to take action that might avoid grapes being downgraded or rejected.
• The timing and methodology of these assessments should be specified in the grower supply agreement and, where an adverse assessment decision is made, evidence to justify the decision should be documented and be accessible to each party in the event of a dispute (this is a requirement of signatories to the Code).

Industry endorsed standard procedures
Australian Grape & Wine has produced an industry endorsed standard procedure for testing winegrapes for Brix or colour and has also produced sampling guidelines for collecting grape samples in the vineyard for Brix and colour assessment.

Although there is currently no industry-endorsed standard procedure for pest and disease assessment in the vineyard, the recently updated booklet on winegrape assessment (Hooper and Wilkes 2022) provides the following useful guidelines:

• Use the disease assessment key from Emmett et al. (2015) to quantify the percentage incidence and severity rating of disease in the vineyard.

• Commence assessment of disease in the vineyard by veraison at the latest, or earlier if resources allow.
• Conduct assessments of disease in association with the winemaker/grape purchaser.
• Ensure assessors are trained in the technical assessment of pests and diseases that can affect wine quality.
• Use an assessment method that produces results that are statistically valid, taking account of vineyard variability. Retain accurate and consistent documentation to support this.
• To ensure thorough monitoring, conduct 200 observations per ‘hot spot’ or block, stopping to assess 20 sites and assessing 10 bunches or leaves at each location by choosing one to five vines. Growers are advised, however, to consult purchasing wineries regarding their disease assessment protocols.

Dispute resolution
Information about dispute resolution can be found on the Dispute resolution page of the AGW website or by contacting the Code Secretariat on codesecretariat@accordgroup.com.au or (02) 9264 9506.

AWRI helpdesk
For assistance with grape assessment or any other technical viticulture or winemaking topic, contact the AWRI helpdesk on (08) 8313 6600 or helpdesk@awri.com.au

References and further reading
ACCC. 2019. Wine grape market study – final report.
Australian Grape & Wine Inc. 2021. Code of Conduct for Australian Winegrape Purchases.
Hooper, A., Wilkes, E. 2022. Winegrape assessment in the vineyard and at the winery.

21 December 2022

Christmas closure and support during the break

The AWRI will be closed over the Christmas/New Year period from midday on Friday, 23 December and will re-open at 8:30am on Tuesday, 3 January 2023.

Affinity Labs
Affinity Labs will be closed from midday on Friday, 23 December and will re-open at 9:00am on Monday, 9 January 2023.

Helpdesk support
Telephone support will be available for urgent or emergency assistance while the AWRI is closed. If you require urgent assistance, please contact:

• Geoff Cowey on 0448 736 145 for winemaking issues.

• Marcel Essling on 0418 816 311 for viticulture issues.

For less urgent queries, please email helpdesk@awri.com.au and the team will get back to you when the AWRI re-opens.

Sustainable Winegrowing Australia support
For any enquiries about Sustainable Winegrowing Australia, please email helpdesk@awri.com.au and the team will get back to you when the AWRI re-opens.

Library
The John Fornachon Memorial Library will be closed from midday on Friday, 23 December and will re-open at 9:00am on Monday, 9 January 2023. Access to the library’s online database will continue to be available 24 hours a day, 7 days a week via the AWRI website.

25 November 2022

Following an eBulletin on 27 October 2022, which focused on downy mildew, this is a reminder that weather conditions in some regions this season are also likely to be highly conducive to the development of powdery mildew and botrytis bunch rot. These diseases have a habit of ‘flying under the radar’ and then emerging just before Christmas or harvest at levels that are very difficult to control. Growers are encouraged to take steps now to avoid disease problems closer to harvest.

Powdery mildew
Powdery mildew in grapevines is caused by the fungus Erysiphe necator. The distinctive grey-white powdery growth affects green tissue, including leaves, shoots and fruit, and has negative impacts on both grape yield and quality. All grapevines are susceptible to powdery mildew, but the risk is greatest in vineyards that were affected by an outbreak in the previous season. Some varieties are particularly susceptible, namely Chardonnay, Semillon and Verdelho. Powdery mildew can develop and progress independently of free moisture. The conditions that favour the development and spread of the disease are mild weather (20 – 30°C), low light levels and relative humidity greater than 40%.

Controlling powdery mildew
The ideal spray program for powdery mildew involves regular applications of protectant chemicals early in the season, effectively protecting all growth from the disease. Stopping the disease from getting established early in the season is critical in reducing the disease load later in the season. Unfortunately, this season has not allowed for early-season sprays to be applied in many vineyards, or the sprays that have been applied have been hit with periods of heavy rain which may have diluted them. These circumstances have created a high level of risk for powdery outbreaks. Where this is the case, action to prevent an epidemic of powdery disease is paramount.

Elemental sulfur is a multi-site fungicide which is not susceptible to resistance and has some curative activity. To gain control of an existing infection using sulfur, good spray coverage is essential. This can be confirmed using wettable paper or a short run with a kaolin clay tank mix. If there are gaps in coverage, it is advisable to adjust one setting on your tractor or spray unit at a time and re-test until good coverage is achieved.

An active powdery mildew infection can be water repellent, so it is important to check that enough spray is reaching all targets. Growers should consider using an adjuvant to improve coverage on what is a hard to wet surface. Some sulfur products such as Thiovit Jet and Microthiol Disperss have an adjuvant built into the formulation, which improves spread on the plant surfaces. Many other sulfur products may require some assistance with spread, so check with your chemical on-seller if an adjuvant is required.

Some single site chemicals are known to have curative activity against powdery mildew but their use against active infection is not recommended due to the increased risk of resistance development. The CropLife Australia recommendation for single site fungicides is that they should be applied before colony formation (preventatively) for powdery mildew control.

Elemental sulfur is in short supply so it’s important to plan how you will use the chemical stock you can access. It is recommended to allocate sulfur to those blocks where a powdery curative is required and use other agrochemicals where powdery mildew has been contained and prevention is still an option. Monitoring is important and instructions on how to recognise powdery mildew are provided in the resources linked below. Consult with your grape purchaser or the AWRI if you are considering chemical options that do not follow the ‘Dog Book’ recommendations for export wine.

Operating a spray unit in the same direction for every spray runs the risk of missing the same hard-to-reach parts of the canopy each time, potentially creating a powdery mildew hotspot. Spraying in a different pattern so that the opposite direction is travelled up the row has the potential to improve overall coverage.

Canopy management practices are an essential part of managing disease risk, especially in challenging seasons. Manipulation of canopy conditions to allow light, air and agrochemical sprays to reach the ‘inside’ foliage helps create a more challenging environment for fungal diseases, including powdery mildew, downy mildew and botrytis bunch rot.

Botrytis bunch rot
Botrytis bunch rot is caused by the pathogen Botrytis cinerea, which is a common environmental fungus that enters grapevine tissue through wounds (including scarring from powdery mildew infection and natural openings) and takes hold once the right conditions are met. Effective Botrytis management requires an integrated approach using both chemical and cultural control measures.

Flowering (E-L 25) and pre-bunch closure (E-L 31) are recognised as the critical growth stages for Botrytis sprays; however, rain and/or high humidity at or around harvest can cause devastating losses in a short period of time. Getting good coverage of the bunch zone is critical with any Botrytis spray, so take the time to check that you are hitting the intended target. Consider the potential entry points for Botrytis infection from initiation of flowering onwards, factoring how growing conditions could affect the risk of Botrytis infection. Also consider previous disease load in your vineyard and the susceptibility of your variety mix when designing control strategies.

New Zealand research investigating various cultural practices to reduce Botrytis risk in high pressure years found that leaf plucking to maintain 70-90% bunch exposure from late flowering to pre-harvest was the most effective treatment (Andrew and Lupton 2013). However, leaf plucking should be applied with care, since excessive leaf removal may result in sunburn, especially if applied later in summer in hot regions. Removing the trash from inside and around developing bunches post-flowering, using a harvester or pulsed air leaf plucker, can also reduce Botrytis risk by taking away a source of Botrytis inoculum and altering the bunch environment for improved airflow and bunch drying.

Reference
Andrew, R., Lupton, T. 2013. Understanding Botrytis in New Zealand vineyards, Auckland, New Zealand: New Zealand Winegrowers: 215 p.

Additional resources
· The AWRI’s resources on powdery mildew
· The AWRI’s resources on Botrytis
· Ask the AWRI publication – Spray application
· Wine Australia’s resources on powdery mildew
· Wine Australia’s resources on Botrytis

AWRI webinars
· Getting the most out of ‘biological’ sprays for Botrytis control (October 2021)
· Late season Botrytis: the disease and options to control it (February 2021)
· Fungicide resistance in Australian viticulture (January 2022)

Acknowledgements
Liz Riley (Vitibit), Kerry DeGaris (Treasury Wine Estates), Warren Birchmore (Accolade Wines), Philip Deverell (Pernod Ricard Winemakers), Scott Paton (Nutrien Ag Solutions) and Scott Mathew (Syngenta Australia) are thanked for their contributions to this eBulletin.

For more information or assistance, please contact the AWRI helpdesk on
08 8313 6600 or helpdesk@awri.com.au.