Fungal Diseases

  1. Powdery Mildew
  2. Botrytis
  3. Trunk Diseases

Powdery Mildew

Current state of knowledge

Powdery Mildew has evolved from being a relatively easy disease to overcome to the most serious of grape diseases in New Zealand - ahead of botrytis and other rots. It has the ability to impart off-flavours that cannot be overcome in wine making, decimate yields, as well as creating injury on berries that provide an entry for botrytis and other end of season rots.

The powdery mildew we dealt with a few years ago was clonal and infection came from a defined early period - from flag shoots and their offspring. Now powdery mildew has the ability to produce fruiting bodies (chasmothecia), bringing the additional burden of ascospore release from chasmothecia which are retained close to the bunch zone in bark. That release is a function of climate, mainly rain events. Early scientific study in New Zealand indicates strongly that ascospore release occurs after rain events through flowering and after flowering. The spores from chasmothecia are thought to act more aggressively in bunches than flag shoot derived spores, but it may be simply that ascospore release that occurs through flowering and after flowering have temperatures more suitable to rapid colonisation of the disease.

If you are interested in Grape Powdery Mildew, the following links are worth checking out:

Preventative Programme for Powdery Mildew Control

The genesis of HML32 occurred in the 2010/2011 season and since then HML32’s efficacy has been improved season on season by the use of hand sprayed and machined sprayed scientific studies with depth and credibility.

The hand sprayed and machine sprayed trials that occurred in 2015-16 and 2016-17 prove that the combination of HML32, sulphur and HML Silco or the alternative of HML32, copper and sulphur are very effective preventative/eradicative regimes for the control of powdery mildew.

There is now an excellent understanding of application timing and the usefulness of various additives and adjuvants (such as HML Silco), bringing together a package that not only compares or betters efficacy from best preventative chemistry, but also bringing with it spray mixes that have eradicative/curative properties.

Here is the recommended Cover spray programme for the Prevention of Powdery Mildew and Botrytis Prevention Spray Programme for 2017-18.

It uses Protectorhml, HML32, HML Silco, and HML Potum, in combination with sulphur and copper fungicides.

Copper fungicides are included to address wet weather diseases such as downy mildew, black spot and phomopsis.

Key facts and principles:

  • Powdery Mildew disease (chasmothecia) are present in most New Zealand vineyards and it is now a disease that requires suppression all season long – including after harvest.
  • Early New Zealand data strongly indicates that rain events trigger ascospore release (from chasmothecia). These releases can occur during flowering or later where temperatures provide Powdery Mildew the ability to move quickly from spore to infection.
  • Greatest care must be taken to protect the current season’s crop from Powdery Mildew when it is at its most susceptible - from 5% cap fall to about one month after completion of flowering. Not only for the disease itself, but for the close connection that exists between it and botrytis infection and other secondary rots.
  • Powdery Mildew is a disease of proximity and while it is unlikely that the disease can ever be eliminated from a vineyard, it is certainly possible to suppress it to very low levels through good viticultural practice and the use of protectant sprays, and at times of need, the use of protectant sprays that also possess eradicant activity.

Product combinations

Many seasons of research confirm different combinations of our products with sulphur and copper fungicides provide either:

  • protectant activity (cover spray)
  • both protectant and eradicant activity (cover spray)
  • specific eradicant activity on established Powdery Mildew infection (high deposition, double pass (both directions)).
  • a plant response to provide significant botrytis resilience and enhanced maturity when applied at the correct growth state (high deposition, double pass (both directions).
  • specific eradicant activity on maturing chasmothecia in the canopy after harvest (high deposition single pass directed at canopy).

The different combinations and rates are shown in the table below.

Spray mix Efficacy rating Powdery mildew Botrytis Enhanced Maturity
Protectant Eradicant
Protectorhml (0.5% solution) and Sulphur (label rate) 1 x      
Protectorhml (0.5% solution), Sulphur (label rate) HML Silco (425g/100L powder) 2 x      
HML32 (1.25L/100L), Sulphur (label rate) 2 x   x  
HML32 (1.25L/100L), Sulphur (label rate) HML Silco (425g/100L powder) 3 x x (cover sprays)
x (high deposition
at bunch line,
double pass* - for
infection only)
x  
HML32 (1.25L/100L), Sulphur (label rate) Copper fungicide (label rate) 3 x x (cover sprays) x  
HML32 (1.25L/100L), HML Potum (300g/100L), Copper (45g metallic copper /100L) 3 Significant
protectant
effect is
achieved
x (high deposition
at bunch line,
double pass* - for
infection only)
x (for maturing
chasmothecia
targeted at canopy
after harvest)
   
HML32 (1.25L/100L) -     x (high
deposition
at bunch
line
*double
pass*)
x (high
deposition
at bunch
line *double
pass*)
Efficacy rating 1 Good efficacy, low pressure
2 Very good efficacy, low - moderate pressure
3 Excellent efficacy - moderate to high pressure
Notes: The combination of HML32, Sulphur, and HML Silco is a particularly effective cover spray as it provides both protectant and eradicant properties.
Please note the combination of HML32, Sulphur, HML Silco and copper fungicide has not been trialled yet.
HML Silco is an adjuvant. It has inadequate efficacy alone.
*both directions

The Cover Spray Programme

There is no one size fits all spray programme for growing wine grapes across the different varieties and regions in NZ. Spray timings should be tempered by best local practices, disease pressure as well as weather.

  Basic programme Additional comments
Beginning of Season/Woolly bud Where there were powdery mildew issues last season, apply

7% lime sulphur
or
2 applications of 3.5% lime sulphur

targeted at the cordon.
This option can go as late as 2 weeks post budburst.
First leaf unfolded to just before flowering – as close as possible to 5% flowering Apply
Protectorhml and Sulphur
at 10-14 day intervals
Recover AFTER each major rain event and begin the ‘clock ticking’ again.

Add a compatible copper fungicide at times to provide cover for wet weather diseases such as downy mildew, black spot or phomopsis

For areas or varieties particularly vulnerable to powdery mildew, add HML Silco to all applications.
Make the last spray (as close as possible to 5% capfall) in this period either:

HML32, Sulphur and HML Silco
or
HML32, Copper and Sulphur.
For areas or varieties vulnerable and with a bad history of powdery mildew infection, make the last 2 sprays either:

HML32, Sulphur and HML Silco
or
HML32, Copper and Sulphur.

to provide robust eradicant activity going into flowering.
Between 5% and 80% capfall If the flowering period is less than 7 days, no applications need to be made in this period. If flowering is wet or extended, apply:

HML32, Sulphur and HML Silco

This can be applied without harm to fruit set.
80% capfall to Pre-bunch closure For the first two applications (7-10 days apart), apply:

HML32, Sulphur and Copper
or
HML32, Sulphur and HML Silco
 
Then apply

HML32, Sulphur and HML Silco

at 7 -10 day intervals
Recover AFTER each major rain event and begin the ‘clock ticking’ again. (Provides curative activity for any powdery mildew spore release) Replace HML Silco with compatible copper fungicide as required for wet weather diseases.
To minimise costs, options include: Substituting with Protectorhml, Sulphur plus HML Silco at times or Targeting the bunchline instead of full canopy
Bunch closure to veraison From one month after 100% capfall, apply

HML32, sulphur and HML Silco

at 10-14 day intervals.
 
Disclaimer: The supply terms of Henry Manufacturing Limited apply to the use of this spray programme. Liability whether in tort (including negligence), contract or otherwise, for any loss, crop or vine injury or crop or vine failure, resulting from the application of this spray programme is excluded. Any user of this spray programme accepts this disclaimer

View the Powdery Mildew and Botrytis Prevention Spray Programme for 2017-18

View the seminar by Dr David Gadoury for more information on the critical period where the plant is at risk of powdery mildew infection.

View our Best Practice - Mixing Guide for HML32.

Eradication of Powdery Mildew Infections

If you have not managed to prevent Powdery Mildew infections this season, there are now TWO pathways to successful manage them. Earlier infections are always far easier to deal with provided the applications are made in accordance with our recommended best practice. With severe infections running through to epidemics, it should still be possible to suppress well and reduce splitting. (See photographic evidence in Farmlands Adjuvant trial where Gewurztraminer was recovered from an epidemic).

The two eradication recipes are

  • HML32 with copper fungicide (45g Cu /100l) and potassium bicarbonate (300g/100l)
  • HML32 with sulphur and HML Silco (Note: this pathway allows for sheep grazing)

Both these recipes have been well validated in various scientific trials.

Updated Research from 2016 Eradication Trial

  • DO NOT include sulphur with the HML32, copper, potassium bicarbonate mix. It reduces the efficacy of the eradication sprays
  • Eradication sprays provide significant forward protection, sufficient that protectant sprays can be resumed subsequently at normal timings, if required.
  • Many trials have confirmed that two applications (7 days apart) are better than one
  • If a single application is all that can be managed – the efficacy can be improved by raising the metallic copper rate from 45g/100l to 67-90g/100l.
  • Severe infections are more difficult to manage but you should at least be able to suppress it. Go to our Best Practice for advice in the recipe and application methods.

Research and trials

View the Powdery Mildew and Botrytis Prevention Spray Programme for 2017–18.

View the Grape Powdery Mildew Prevention Trial 2016-17, Ngatarawa Rd (machine sprayed).

View the Grape Powdery Mildew Prevention Trial, 2015–16.

View the Grape Powdery Mildew Eradication Trial, 2016.

View the Farmlands Adjuvant Trial – Preparation of Trial Site 2015-16.

View our Best Practice - Eradication of Powdery Mildew Infection 2017.

View the full report on the HML32 powdery mildew eradication trial.

View the Farmlands presentation/report on their independent powdery mildew eradication screening trial, which includes HML32 formulations.

Botrytis

Botrytis is a disease that is present in the environment wherever there is dead plant material. In the New Zealand context, it uses multi-pathways to establish infection in wine grapes and therefore broad strategies are required to prevent it.

Direct infection during flowering has perhaps the most potential to be damaging, where the infection remains dormant/latent awaiting sugar accumulation within the berry and rain event/s to set it off – leading to end of season bunch botrytis or slip skin. Click here for a presentation with excellent images of latent botrytis infection before any visible symptoms and also examines between botrytis, slipskin and water.

Another major pathway is where botrytis is a secondary disease where the berry skin has been previously weakened say following a powdery mildew infection, or less commonly where there is physical damage caused by insects.

Good cultural control begins with good pruning, leading to well balanced and even fruiting through the vine, avoiding heavy growth in the head or at end of canes. Blowing out flowering trash from the bunches, leaf plucking to allow air movement and quicker drying times, and even mechanical trunk shaking can all assist to lower botrytis risk.

Well timed fungicidal sprays are also important, and this is where HML32 with additives can be particularly useful as infections from both powdery mildew and botrytis are directly prevented.

In addition, trial work in the 2015/2016 season very much supports that if HML32 is used at the correct plant growth timing, thickening of the berry skin occurs resulting in considerable resilience to botrytis including slip skin.

Strategies to thicken berry skin have a part to play as have strategies to loosen bunch structure reducing berry to berry pressure.

Watch this video to see the difference applications of HML32 at particular timings made to an end of season slipskin infection in a vineyard in Hawke's Bay.

View the Enhanced Maturity and Botrytis Trial 2016.

View the Powdery Mildew and Botrytis Prevention Spray Programme for 2017-18.

View the Presentation ‘Botrytis, Slip Skin and Water’ - Dr Gareth Hill Plant and Food Research 2017.

Trunk Diseases

Henry Manufacturing has undertaken very little work in the area of grape trunk diseases.

At the 2017 New Zealand Organic Winegrowers Conference, the following presentation (listed with permission of its author) was given by Francois Dal. It provides an unusual degree of insight into how trunk diseases (short and long term) can be dealt with by well planned and executed pruning.

We list this presentation here as we wish to support good viticultural practice.

View the presentation Pruning to limit trunk disease, Francois Dal