Agrochemical Updates, eBulletin

Downy Mildew update

Weather conditions have been conducive to downy mildew infection and symptoms of the disease have been reported in some regions. This document summarises the important issues around control.

1.1 Chemicals registered for use

The recommendations section of Agrochemicals registered for use in Australian Viticulture 2010/2011 (DogBook) lists all the active constituents registered for downy mildew control in Australian viticulture. The restrictions on use are guidelines imposed on grapes destined for export wine to ensure that the chance of residues is minimal.

phosphorous acid Y Agri-Fos 600, ChemPhos 400, Country Phospot 400, Country Phospot 400 pH 7.2, Country Phospot 600, Dominator 600, Fungi-Fos 400, Fungi-Fos 400 pH 7.2, Sprayphos 400, Sprayphos 620, Throw Down Not recommended for use on grapes destined for export wines. Consult your winery/grape purchaser.
azoxystrobin K Amistar 250 SC, Mirador 250 SC Use no later than 80% capfall.
benalaxyl + mancozeb D + Y Galben M
chlorothalonil Y Applonil 720, Barrack 720, Barrack Betterstick, Bravo 720, Bravo Weather Stik, Cavalry 720 SC, Cheers 720, Cheers 720 Weathershield, Chemtura Chlorothalonil, Chlorothalonil 500 SC, Chlorothalonil 720, Echo 500SC, Echo 720, Echo 900 WDG, Elect 500, Fung-o-nil 500, Unite 720, Unite Ultrastick, Whack, Whack 900 WG
dimethomorph X Acrobat SC
metiram Y Polyram DF
oxadixyl + propineb D + Y Rebound WP
zineb Y Zineb
trifloxystrobin K Flint 500 WG (suppression only) Use no later than E-L growth stage 31 (before bunch closure).
pyraclostrobin K Cabrio, Cabrio 200WG Use no later than E-L growth stage 31 (before bunch closure). Do not use within 63 days before harvest.
captan Y Captan 900 WG, Captan WG, Merpan Use no later than 30 days before harvest.
copper ammonium acetate Y Cop-IT
copper ammonium complex Y Copperguard, Liquicop
copper cuprous oxide Y Nordox 500, Norshield, Norshield 750 WP, Norshield WG
copper hydroxide Y Blue Shield DF, Champ Dry Prill WG, Flo-Bordo, Hydrocop DF, Kocide Blue Xtra, Kocide Opti
copper hydroxide + mancozeb Y + Y ManKocide DF
copper octanoate Y Tricop
copper oxychloride Y Copper Oxychloride, Copper Oxychloride WP, Coppox WG, Country Copper Oxychloride 500 WP, Oxydul DF
copper sulfate tribasic Y Bordeaux WG, Cuprofix Disperss, Tri-Base Blue
copper sulfate tribasic + mancozeb Y + Y Novofix Disperss
dithianon Y Delan 700 WG
mancozeb Y Dithane 430 SC, Dithane Rainshield Neo Tec, innova Mancozeb 750, Kencozeb 750DF, Mancozeb 750 DF, Mancozeb 750 WG, Mancozeb 800, Mancozeb DF, Mancozeb DG, Manfil, Manzate DF, Penncozeb 420 SC, Penncozeb 750DF, UniZeb 750 DF
metalaxyl – M + copper hydroxide D + Y Ridomil Gold Plus
metalaxyl – M + mancozeb D + Y Ridomil Gold MZ WG
metalaxyl + copper oxychloride D + Y Axiom Plus, Medley Plus
metalaxyl + mancozeb D + Y Axiom MZ 720, Maxyl, Medley MZ, Zeemil MZB 720 WP

Scarcity of some chemicals in some markets has been reported. The companies that source and distribute chemicals are aware of the high demand and short supply of some products in some regions. They are actively looking to meet demand wherever possible. Chemical availability does change so keep in contact with your agrochemical supplier and make them aware of your requirements.

1.2 Managing the disease

Extract from Managing Downy Mildew (Winning the war!) by Peter A. Magarey (Innovators Network Module INO904). Visit for the full document.

Fungicide Types: The two main types of downy mildew fungicide are classified according to their timing in relation to infection events. They are best applied when they are most effective, that is either pre- or post-infection.

Pre-infection fungicides (protectants): These protect the vine by preventing infection. Many belong to the Group M fungicides and are not systemic (phosphorous acid and fungicides in Groups 11 and 40 are exceptions). The non-systemic (or contact) fungicides provide a protective barrier on the surface of the foliage where they stop the spores germinating. Since downy invades through the stomates, apply contact fungicides to cover the undersides of leaves – the most difficult place to spray. They must be re-applied prior to an infection event if there is sufficient growth of leaves or of developing berries. Apply the sprays as close as possible before infection. Access to forecasts of downy mildew events will help time these sprays best.

Post-infection fungicides (eradicants): These are sometimes known as systemics – but note: some pre-infection fungicides are also systemic. The post-infection fungicides kill the pathogen inside infected tissue if they are applied at the right time. They do not eradicate the disease from the vineyard but, being systemic, they are quickly absorbed into the sprayed foliage and are rain fast within 2-3 hrs of spraying. Because Ridomil is usually mixed with mancozeb it simultaneously provides a protective shield against new infection. The post-infection fungicides are more expensive but are able to ‘eradicate’ the downy pathogen from within infected tissue. Consequently, apply these fungicides only when needed and then, as soon as possible after an infection and before oilspots appear i.e. in warm conditions, within 5 days post-infection. Like all fungicides, good coverage is important. The post-infection fungicides include Ridomil Gold® (a Group D fungicide) and phosphonate e.g. Foli-R-Fos® (Group 33). Because resistance to Ridomil has been reported, Australian management strategies recommended only 1-2 applications per year.

Phosphonate (phosphorous acid) is not currently (2010/11) accepted for use on grapes for export wines and is discussed below.

Spray Timing

Because warm wet weather drives downy mildew, for optimum control, apply sprays in relation to primary and secondary infection events. Where possible, access weather forecasts and predicted times of high disease risk and spray before the disease develops. Monitor and interpret the weather that followed to determine if infection occurred and adjust spray type and timing accordingly. If available, seek assistance from regional disease alert services.

You may have access to an automatic weather station (AWS) that monitors temperature, rainfall, relative humidity, leaf wetness and daylight and dark at 10 (or 15) minute intervals. If so, you may process the above data through DModel, an Australian simulation model of downy mildew, for specific advice on the timing of primary and secondary infection events critical to best control of disease. In some regions, industry-based services such as CropWatch and CropWatch Online use a network of AWS to provide region-wide advice of disease risk in different localities. These services provide a weekly e-mail and fax-out advisory service and have helped minimise the number of sprays needed for effective control of downy mildew, especially in dry seasons.

1.3 Lessons from the Hunter Valley – Liz Riley

Coverage is everything – high water volumes applied with equipment that is able to get thorough coverage is critical. CALIBRATE and check coverage. Using partical film technology (i.e. parasol) to assess water rates is a quick and easy way to evaluate coverage.

The Hunter has confirmed resistance to metalaxyl in some sites. This is the result of ongoing use in high pressure sites after an infection, i.e. as an eradicant. The lesson is that if you can’t get in with an ‘eradicant’ immediately post infection i.e. prior to oil spots, you probably shouldn’t. Ongoing Ridomil applications won’t always kill it – it may just suppress it and you have ongoing creeping infections; these are fuelled by dew and free moisture not just conventional infection periods.

In the absence of metalaxyl and phosphorous acid, high rates of copper with new formulations such as Kocide Opti have been fairly effective. Coupled with trimming to get more air in for canopy drying you can have a reasonable chance of getting to grips with the infection and then maintaining coverage on all new foliage.

The biggest challenge is rain at flowering where the flowers, caps, anthers hold the water so you can get an infection on flowers but not on the leaves, as they haven’t met the 10 10 24. We have found Cabrio has been very effective in this situation – although Cabrio is not meant to be used as an eradicant. We tend to use Cabrio at flowering anyway so it is a bet each way in seasons like this.

There is no room in bad years to run a lean fungicide program – 2-3 sprays for the season is not enough. Copper at 10-12 day intervals while the vines are growing strongly and rain persists. We are “growing out of cover” at these intervals and often downy is appearing on laterals rather than primary leaves as they had little or no cover when a spray was applied, and then rapidly grow, an infection occurs. The weather stays moist and a secondary infection occurs all prior to the next cover spray. So shorter intervals is also part of the protectant strategy – 14 days is too long when pressure is high.

The really important part is to get through flowering and set and have it at bay. Where it is permitted for use, control with phosphorous acid in this period with one or two sprays would be the go. It would potentially need following up or combining with copper to maintain protectant cover.

We are now about to do our second wire lift and have considerable downy on foliage just above the flower/fruit zone and are making sure we spray before we lift to get really good coverage to try to minimise the downy spores that will potentially wash down into the fruit in any subsequent rain events – this is where the trimming option has some value as you can then chop it out and the new growth will be clean.

1.4 Phosphorous acid

Phosphorous acid is a registered fungicide with post-infection capabilities, but residues in wine are to be expected if it is used at any time during the growing season. For this reason, exporting wineries have no tolerance for fruit that has been treated with this active. The Dogbook recommendation states that phosphorous acid should not be applied to fruit destined for export wines. Please contact your winery or grape purchaser prior to any phosphorous acid application.

The tables below separate our major export markets into those that have a tolerance for phosphorous acid residues and those that do not. In doing so, it highlights the potential for ‘batching’ grapes and wine according to market. This will not be an option for wine companies that export to markets that do not have any tolerance for phosphorous acid residues in wine. Contact your winery or grape purchaser prior to any phosphorous acid application.

1.4.1 Export market tolerance towards phosphorous acid residues

Australia has a maximum residue limit (MRL) for phosphorous acid (phosphonate) in grapes of 50 mg/kg.

The export markets* that have no tolerance for any phosphorous acid residue or have a default level of 0.1 mg/kg are:

Argentina Korea (Republic of)
Brazil LCBO (0.1 mg/kg)
Canada (0.1 mg/kg) Malaysia
Chile Philippines
China Russia
Codex Singapore
Hong Kong Taiwan
India Thailand
Indonesia Vietnam

*Listed in the AWRI MRL database.

The export markets* that have an MRL that is equal to or greater than 50 mg/kg are:

Belgium (100 mg/kg) South Africa (100 mg/kg)
Denmark (100 mg/kg) Sweden (100 mg/kg)
European Union (100 mg/kg) Switzerland (100 mg/kg)
France (100 mg/kg) The Netherlands (100 mg/kg)
Germany (100 mg/kg) Turkey (100 mg/kg)
Ireland (Republic of) (100 mg/kg) United Kingdom (100 mg/kg)
Japan (70 mg/kg) United States of America **
Norway (100 mg/kg) New Zealand **

*Listed in the AWRI MRL database.
** Phosphorous acid is exempt from the requirement of an MRL.
Note: Even though these markets have a greater tolerance level than the Australian MRL, wine from Australia must not exceed 50 mg/kg.

1.4.2 Additional sources of phosphorous acid residue

Foliar fertiliser sprays and diammonium phosphate (DAP) can be a potential source of phosphorous acid in fruit and wine. This may be a function of the manufacturing process. Prior to the use of products that contain phosphorous, it is strongly advised that a process is put in place to ensure that the product is fit for purpose and does not contain phosphorous acid. Winemakers should not overlook the potential for DAP to contribute to detectable levels of phosphorous acid even in the absence of direct vineyard application.

1.4.3 Phosphorous acid residue study

The following points come from Final Report to GWRDC AWR 04/10: Morgan, A., Bell, S-J. and Wicks, T. (2005). Persistence of Residues of Potassium Phosphonate (Phosphorous Acid) in Grapes and Wine.

Vineyard trials were conducted from 2003-2005 in Riverland, SA and Griffith, NSW. Note: the extent of the study was limited in scope (treatments were not fully replicated) and the findings should be used as a guide only.

  • Phosphorous acid residues in fruit from the 2004 and 2005 harvests ranged from 6.6 – 46.5 mg/kg and 1.0 – 24.0 mg/kg respectively.
  • Phosphorous acid residues in wine were generally higher than in the berries.
  • In all instances bar one, the requirements of the Australian MRL (50 mg/L) were met.
  • In the instance where the Australian MRL was exceeded, 6 spray applications were applied during the season and the last application was 8 days before harvest.

  • The only undetectable phosphorous acid residue in wine was from the application of one spray (1.2 L/ha active constituent) applied 124 days before harvest. A replicate of the same treatment resulted in a residue in wine despite no residues in the berries.
  • Residues were found in wine even when spraying ceased by fruit set and where only one spray was applied early in the season.
  • Even when there was no detectable phosphorous acid residue in the berries in the case of a single early spray, there was a residue in the corresponding wine.
  • Phosphonate residues were found to carry-over from one season to the next when 4 or more applications of phosphonate had been applied.
  • For markets with an MRL or the Australian market, one or two sprays of phosphonate prior to veraison could conservatively be applied in a season without exceeding the Australian MRL. The number of applications of phosphonate should be reduced if previous phosphonate sprays had been applied in past vintages.