Powdery Mildew Fungicide Programs

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08/02/20 Sciences Reference this

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Fungicide programs used to manage powdery mildew (Erysiphe necator) in Australian vineyards

Introduction

Powdery mildew (Erysiphe necator) is one of the most economically important diseases of the European grapevine, Vitis vinifera, both in Australia and world-wide. Susceptibility varies between cultivars; however, the fungus is able to infect all green tissues and can cause severe damage to leaves and berries (????). In seasons with favourable weather conditions or when limited control measures are implemented; the disease can be severe on susceptible varieties and result in yield reduction and loss of fruit quality. Less than 5% disease coverage can result in off flavours in the wine (Stummer et al. 2005). In Australia powdery mildew overwinters both as chasmothecia and perennated within buds; but it is the flag shoots that develop from these infected buds that are the primary inoculum source (????). This contrasts with the eastern United States and northern Europe, where chasmothecia and in California where both sources of infection are relevant (????). Late season infections and the amount of inoculum carried over into the following season has a significant impact on epidemic development (????). The epidemics can quickly progress during the growing season due to the recurrence of both primary (sexual) and secondary (asexual) infections (????).

Fungicide programs are used to maintain the grapes as disease-free. However, if weather conditions are favourable for disease and if appropriate sprays programs are not maintained; especially if fungicides are not applied between flowering and berry set) low levels of powdery mildew can still occur in some seasons. In Australia, since the 19??’s, growers have been advised to manage powdery mildew using a fixed-interval foliar fungicide program, with a focus on early season management to prevent the initiation of an epidemic by controlling inoculum loads while they are small. The program that is typically recommended calls for fungicide applications to be made at two, four and six weeks after bud burst, followed with further applications if monitoring showed powdery mildew to be present or weather conditions are conducive for disease development. The regular application of fungicides can potentially lead to unjustified sprays, whereas applications based on growth stage do not account for current conditions and lead to the unjustified application or poor spray timing. Another common error is to delay fungicide application until the disease is detected in the vineyard. Symptoms do not normally become obvious until several weeks after the disease is well established, several weeks after the epidemic was initiated. By this time control is at best difficult, if not impossible (???).

Powdery mildew is favoured by dry weather but humid weather; the optimum temperatures are between 20 and 30C (Delp 1954, Myyer et al 2007) and relative humidity that is greater than 45%. A range of models are available to support growers with the application of fungicides to control powdery mildew (e.g. ????). They are rarely used in Australia as the major source of inoculum comes from existing infections within the vineyard; as apposed to native vegetation. Therefore, if the epidemic can be successfully controlled early in the season with fixed-interval sprays, the total number of applications can be minimised (????).

There are a wide range of active ingredients available for the control of powdery mildew in Australia (Essling and Lord 2018). Considerable information has been derived from efficacy trials, both as part of the fungicide registration process and with an aim of refining fungicide programs (e.g. Wicks and Hitch ???). Besides the expectations of efficacy; growers also make fungicide decisions based on the cost, availability, ability to treat additional pests (i.e. erinose mite) or diseases (i.e. downy mildew), compatibility for tank mixing with other active ingredients and concerns about phytotoxic effects (????). Fungicide resistance is a growing issue across horticultural crops; including grapevines (????). Growers are supported with advice on managing the potential for fungicide resistance by the ????, they recommend a maximum number of applications for site-specific fungicide groups per season (Essling and Lord 2018). Fungicides are applied to horticultural crops in Australia based on a unit of canopy volume as opposed to the land area; therefore, application rates (and the amount of water recommended for canopy coverage) increases as the canopy grows (????).

While optimum control strategies have been developed; and the suitability of a range of active ingredients assessed; there is very little information is available on what products are applied and how they are used by grape growers in real world situations. This includes the timing of the start of fungicide programs, if the spray program focuses on early season or mid-season controls, the rates of active ingredients used, the use of wetting agents and water rates applied, and the responsiveness of spray programs to seasonal conditions. The aim of this work is to gain a better understanding of these trends; so that advise on spray programs to be optimised, and the efficiency of spray programs to be improved.

Methods

Virtually all wineries that export from Australia require a record to be maintained of all of the pesticides applied to the grapes that they are supplied; these are colloquially known as ‘spray diaries’. The records are reviewed by the grape purchaser to ensure that only registered chemicals have been applied at the appropriate rates and that all appropriate withholding periods have been met; as per the Essling and Lord (2018). This minimises the chance of agrochemical residues being detected in Australian wine in any export markets. Most larger companies collate the spray records for each block electronically, with the growers updating their pesticide using online software prior to harvest.

A database was sourced from the largest spray diary software company in Australia. These growers supplied at least 10 individual wine companies and approximately ???% of the Australian grape harvest so we felt that this sample was of a sufficient size to be representative of industry practices in Australia. While pesticide records were available for most Australian wine regions, the thirteen regions that recorded over 1000 individual fungicide applications were chosen for further analysis (see Table 1) so that the spray program used by an individual large grower could not bias results. Likewise, the varieties were restricted to the seven most commonly planted in Australia, Cabernet Sauvignon, Chardonnay, Merlot, Sauvignon Blanc, Shiraz, Pinot Noir and Semillon. Spray records were not available for all year, region and variety combinations; and this meant that some combinations needed be excluded from the analysis so that valid interaction terms could be reported.

Relevant information included in each database entry included; the region (geographical indicator) the vineyard was in, the date when the fungicide was applied, the grape variety it was applied to, the application rates for the water and active ingredients, the active ingredient and its formulation (powder, liquid etc.), the pest or disease being targeted (in this case powdery mildew) and the phenological stage of the vines.

The database contained duplicates where products or formulations varied across an individual block, for example if two different brands of the same active ingredient were used; or occasionally when an application was spread over multiple days, most likely due to a delay in application when weather conditions changed. To remove these duplicates, data was combined when individual records were made for the same active ingredient on a similar date or growth stage. In a similar manner the spray diary database recorded all entries; however occasionally the purchaser of the fruit from a block of vines would change during the season and the new purchaser would use a different pesticide use tracking system. This would result in an incomplete entry, as the grower was no longer required to complete this electronic diary. Application records were reviewed by grower, variety and season and any unusual (normally very low) records were removed. This data cleansing resulted in the removal of approximately 5% of the spray records.

All data processing was conducted in Microsoft Excel 2016 (Redmond, WA, USA) and statistical analysis was completed using Minitab 18.1 (Minitab, Inc., State College, PA, USA). As all data was categorical and did not conform to a normal distribution; therefore, it was processed using a Box-Cox transformation, using a calculated optimal λ, prior to analysis using a general linear model.

Results

The fungicide application data for fifteen Australian Geographical Indicator (GI) regions, eight varieties were collated, this gave a total of approximately 295,000 active ingredients applied over approximately 270,000 fungicide applications during the seven vintages (Table 1). The most applications were recorded from the Riverina (GI) region despite there being no data collected from this region in 2012. The least number of applications was made from the Tasmania GI region, which represents less than 1% of Australia’s total wine grape production. Note that most enterprises and management units provided data over multiple seasons so that the number of active ingredients cannot be divided by the number of management units to give an average number of active ingredients applied per block (Table 1). Australian viticultural production is characterised by three broad production systems; the inland regions that irrigate from the Murray-Darling river system (Riverland, Murray Darling, Swan Hill, and Riverina) and produce a commercial grapes and wine generally at high yields (targeting greater than 20t/ha). The warm premium or traditional winegrowing regions such as the Clare and Barossa valleys, McLaren Vale, and Coonawarra, where yield targets are lower, and the canopies are generally smaller and less dense. The cooler regions such as the Yarra Valley, Tasmania and the Adelaide Hills also experience higher rainfall and often maintain their canopies using the traditional vertical shoot positioning training system, they have a higher disease pressure. Using this categorisation makes the description of the results and the discussion of the implications easier.

The average number of active ingredients applied varied significantly between the varieties and the regions (figure 1a). Generally cooler and wetter regions such as Tasmania and the Yarra Valley applied more active ingredients than warmer regions. Although they record higher temperatures the regions in the Murray valley (Riverland, Murray Darling, Swan Hill and the Riverina) applied more active ingredients than the premium regions such as the Barossa and Clare valleys. In many regions (Margaret River, Adelaide Hills, Swan Hill, Coonawarra, McLaren Vale and Langhorne Creek) Chardonnay and to a lesser extent Pinot noir had significantly more active ingredients applied compared to the other varieties. Likewise, Sauvignon Blanc and/or Cabernet Sauvignon often had less active ingredients applied compared to the other varieties, especially in Tasmania and Wrattonbully. Some of the varieties by region combinations were uncommon, for example Pinot Noir in Margaret River and Semillon in Wrattonbully and Coonawarra, hence the large uncertainty with these results (figure 1a). The Riverland, Riverina and Clare valleys had a remarkably consistent number of active ingredients used across all the varieties. The number of active ingredients used varied significantly between seasons (figure 1b). In South Eastern Australia (all regions except Margaret River) most regions applied significantly more active ingredients in the 2012 and 2017 vintages. The two regions that didn’t follow this trend are the Yarra Valley which used significantly more active ingredients in 2018 and Tasmania which used similar numbers of active ingredients across most seasons, except in 2016 when less were used, likewise Margaret River had a relatively consistent use of active ingredients, except for 2012 when less was used. Variation in the number of active ingredients used was less between varieties than it was between seasons, where a variation of 20% within a region was not uncommon.

The number of fungicide application events followed a very similar trend across varieties, seasons and regions, to the number of active ingredients applied (data not shown). On average 1.09 fungicides were applied per application event; this was significantly higher in Margaret River and Coonawarra. The Yarra Valley, Wrattonbully, Murray Darling, Swan Hill, Langhorne Creek and Clare Valley saw a significant increase in the number of fungicides were applied per application event between 2012 and 2018 (Figure 2). Three regions (Riverland, Padthaway and the Barossa Valley) maintained fungicide programs that based on applying one active ingredient at a time. Pinot Gris received significantly more active ingredients (1.16) per fungicide application than the other varieties (data not shown).

As expected the warmer inland regions (Riverland, Murray Darling and the Riverina) generally started and finished their fungicide programs earlier than the cooler regions (e.g. Tasmania) (Table 2). The Yarra valley started its fungicide program surprisingly early and at an earlier G-L stage compared to the other cool regions (Tasmania and the Adelaide Hills). As would also be expected the cooler regions maintained a spray program over a longer period than the warmer regions, and most of the warm regions concluded their fungicide application programs prior to the new year. Generally; the premium regions and the inland irrigated regions maintained a longer average interval between fungicide applications (approximately 14 days) compared to the cooler regions (12.5 days); the exception to this was the Riverland which although an inland commercial region maintained an average interval of 12.7 days. Swan Hill and the Yarra Valley commences their fungicide program at a significantly earlier growth stage compared to the other regions. The other inland and cool regions also started their fungicide programs at an earlier growth stage than the warm premium regions. The growth stage of the final fungicide application was similar across all the regions; the only region that applied fungicides on average after sugars had begun to accumulate (E-L 34) was the Margaret River.

The timing of fungicide applications can be critical for the effective control of Powdery Mildew. When the number of fungicide applications was averaged by growth stage and then compared to the date of the growing season a significant positive trend was seen between winter bud (E-L 1) and berries still hard and green (E-L 33); showing that relatively more fungicide applications were made earlier in the season and at less advanced stages of growth, than at later stages of growth. Growth stages above E-L 33 were not included in the regression analysis as beyond this stage of development the fruit is close to harvest and fungicide application is reduced to minimise the chances of residues in the wine. A similar response was seen when the growth stage (r2 = 0.49), as opposed to the date of the growing season was used as the predicting variable (data not shown).

Approximately 70% of the active ingredients applied across all regions, varieties and seasons were sulphur (Figure 4), most of the balance were spread across six activity groups (Table 3). The seasonal variation in the proportion of the fungicide program within a region that was comprised of sulphur was relatively small compared to the variation between regions. The inland irrigated regions tended to favour the use of sulphur, while the use of other actives was favoured in the cooler regions. Surprisingly the Barossa Valley also used relatively little sulphur, which was in contrast to the other premium regions.

Most of the synthetic fungicides have a single mode of action, and even if they are multisite there is an increased risk of the development of resistant strains of powdery mildew if appropriate practices are not followed (???). Overall there were very few occurrences of incorrect fungicide use, with approximately 550 occasions where the recommended number of applications per block, per season, was exceeded and 450 occasions where the number of consecutive applications of the same fungicide chemical family were exceeded. This represents 0.15-0.19% of the approximately 295,000 fungicide applications analysed. The chemical family where both the number of applications per season and number of consecutive applications was most commonly exceeded was demethylation inhibitors, followed by quinone outside inhibitors (Table 3). In contrast the phenyl-acetamide and aryl-phenyl-ketone fungicides were very rarely applied incorrectly.

The sum of the evapotranspiration during the thirty days following the separation of the first leaf (E-L 7) was correlated with the number of active ingredients applied to control powdery mildew through the growing season for eleven of the fourteen regions (Table 4) and for the regions pooled together (Table 4, Figure 5). The regions that did not show a relationship between evapotranspiration and the number of active ingredients applied were generally cooler and wetter (lower ETo) and has a higher number of applied active ingredients. While significant; the relationship between ETo and the number of active ingredients applied was not that strong when the data was pooled across the regions (Table 4, Figure 5). In contrast for many of the individual regions the relationship between the ETo and the number of active ingredients applied was very good (r2 < 0.75).

Discussion

The order of fungicide active application has little effect on the level of control (Wicks and Hitch 2002)


Table 1: Fungicide application data for Chardonnay, Pinot Noir, Pinot Gris, Semillon, Merlot, Shiraz, Sauvignon Blanc and Cabernet Sauvignon in fifteen Australian Geographical Indicator regions over the vintages from 2012 through to 2018.

Geographical Indicator Region

Number of Enterprises

Number of Blocks (management units)

Number of Fungicide Applications

Number of Active Ingredients Used

Adelaide Hills

179

1141

21955

24238

Barossa Valley

326

3150

32727

33501

Clare Valley

98

669

8361

9374

Coonawarra

104

520

9123

10445

Langhorne Creek

97

1104

16592

18608

Margaret River

119

1021

18319

21321

McLaren Vale

297

1655

28059

30406

Murray Darling

404

2470

43232

48283

Padthaway

54

701

12367

12700

Riverina

376

2722

25574

27929

Riverland

237

1531

24115

24859

Swan Hill

53

456

7744

8263

Tasmania

23

217

7096

7560

Wrattonbully

73

612

9881

10472

Yarra Valley

44

330

6541

7171

Total

2484

18299

271686

295130

Geographic Indicator Region

Date of first fungicide application (date)

Date of last fungicide application (date)

Length of fungicide application season (days)

Average interval between fungicide applications (days)

Growth stage when first fungicide application made (E-L stage)

Growth stage when last fungicide application made (E-L stage)

Tasmania

8/Oct (1.2)

3/Feb (9.3)

118.5 (6.98)

12.9 (0.06)

7.6 (0.02)

33.8 (1.67)

Yarra Valley

17/Sep (1.3)

7/Jan (9.6)

111.6 (7.16)

12.4 (0.06)

5.2 (0.02)

33.8 (1.69)

Margaret River

27/Sep (0.8)

17/Jan (7.0)

112.4 (5.07)

12.6 (0.04)

7.4 (0.01)

34.5 (1.44)

Adelaide Hills

3/Oct (0.6)

16/Jan (5.4)

105.3 (3.83)

13.6 (0.02)

8.2 (0.01)

33.2 (1.26)

Riverland

21/Sep (0.6)

22/Dec (5.5)

91.5 (3.88)

12.7 (0.02)

8.7 (0.01)

33.5 (1.27)

Wrattonbully

1/Oct (0.9)

16/Jan (7.2)

106.8 (5.22)

16.0 (0.04)

8.2 (0.01)

33.4 (1.46)

Murray Darling

19/Sep (0.4)

17/Dec (4.0)

89.6 (2.78)

13.4 (0.01)

7.0 (0.00)

33.4 (1.09)

Padthaway

24/Sep (0.8)

31/Dec (6.5)

98.1 (4.70)

14.4 (0.03)

9.7 (0.01)

32.9 (1.39)

Swan Hill

14/Sep (1.0)

19/Dec (7.8)

95.2 (5.71)

14.0 (0.04)

5.0 (0.01)

32.9 (1.52)

Coonawarra

8/Oct (0.9)

11/Jan (7.5)

95.2 (5.52)

15.2 (0.04)

9.1 (0.01)

32.3 (1.50)

McLaren Vale

29/Sep (0.5)

26/Dec (5.1)

88.1 (3.55)

14.3 (0.02)

10.3 (0.01)

32.7 (1.22)

Langhorne Creek

3/Oct (0.6)

25/Dec (5.6)

82.9 (3.97)

14.4 (0.03)

10.4 (0.01)

32.5 (1.28)

Riverina

25/Sep (0.4)

15/Dec (4.1)

81.0 (3.26)

15.6 (0.02)

7.1 (0.00)

32.6 (1.30)

Clare Valley

6/Oct (0.8)

21/Dec (7.0)

76.0 (5.07)

15.3 (0.04)

10.6 (0.01)

31.7 (1.44)

Barossa Valley

5/Oct (0.4)

22/Dec (4.5)

77.8 (3.11)

15.7 (0.02)

10.6 (0.00)

31.9 (1.14)

Table 2: The average timing and growth stage of the first and last fungicide applications, the average interval between fungicide applications and the time between the first and last fungicide applications across geographic indicator regions.

Data in brackets represents Fishers LSD 5%. As there was no data collected for the Riverina in 2012, the analysis was completed twice; once excluding the Riverina and then excluding the 2012 vintage so that all contrasts could be included.

Fungicide Chemical Family

Number of applications

Applications per Season (average number of blocks)

Consecutive Applications (average number of blocks)

Quinone outside Inhibitors

1

1460.6

1769.7

2

329.9

205.0

3

27.3

9.1

4

1.0

0.0

Aza-naphalenes

1

1224.3

1690.7

2

440.7

288.1

3

55.0

7.0

4

4.1

0.0

Demethylation Inhibitors

1

1785.0

3364.6

2

997.1

575.0

3

223.0

32.9

4

34.7

4.7

5

6.3

0.1

6

2.3

0.0

Amines (Morpholines)

1

1444.0

1756.9

2

648.4

514.3

3

22.0

7.7

4

0.4

0.0

Phenyl-acetamide

1

282.8

300.0

2

32.0

24.0

3

2.0

1.6

Aryl phenyl ketone

1

576.9

617.7

2

58.4

42.7

3

3.7

0.6

LSD (5%)

302

501

Table 3: The number of applications and the number consecutive applications of fungicide groups with single site activity per seasons, averaged across seven cultivars and fifteen Geographical Indicator regions. The multisite fungicides (primarily Sulphur) were excluded from this analysis.

Fungicides are categorized as per the Crop Life Australia Powdery Mildew management strategy for grapes, and the values highlighted in grey exceed the number of recommended applications. When consecutive applications occurred across multiple seasons they were recorded against the season when the final application was made. LSD is a Fishers LSD at 5% for the analysis across years.

Region

Number of active ingredients

Average Evapotranspiration (mm)

Slope of ETo vs number of Active Ingredients

r2

significance

Australia

na

na

-0.057 (0.0053)

0.538

***

Tasmania

9.11 (1.23)

96.4 (26.3)

-0.049 (0.0266)

0.405

ns

Yarra Valley

8.65 (1.46)

81.6 (26.3)

-0.055 (0.0566)

0.188

ns

Margaret River

9.33 (1.20)

100.8 (26.3)

0.058 (0.0272)

0.480

ns

Adelaide Hills

9.04 (1.13)

131.3 (26.3)

-0.031 (0.0264)

0.222

ns

Riverland

8.49 (1.19)

145.1 (26.3)

-0.033 (0.0086)

0.746

*

Wrattonbully

7.35 (1.12)

129.1 (26.3)

-0.023 (0.0077)

0.639

*

Murray Darling

8.41 (1.15)

138.3 (26.3)

-0.043 (0.0062)

0.904

***

Padthaway

6.91 (1.13)

114.6 (26.3)

-0.033 (0.0138)

0.533

+

Swan Hill

6.74 (1.18)

105.1 (26.3)

-0.044 (0.0172)

0.568

*

Coonawarra

7.13 (1.12)

119.5 (26.3)

-0.045 (0.0169)

0.591

*

McLaren Vale

6.99 (1.13)

131.8 (26.3)

-0.089 (0.0308)

0.624

*

Langhorne Creek

7.09 (1.17)

141.7 (26.3)

-0.071 (0.0124)

0.868

**

Riverina

6.14 (1.21)

129.2 (28.3)

-0.035 (0.0056)

0.928

**

Clare Valley

6.30 (1.18)

143.3 (26.3)

-0.064 (0.0137)

0.812

**

Barossa Valley

5.53 (1.17)

141.3 (26.3)

-0.052 (0.0119)

0.795

**

Table 4: The relationship between the evapotranspiration for the thirty days following the first leaf separating from the shoot tip (E-L 7) the number of active ingredients applied over seven seasons in fourteen Australian wine regions.

Notes:

The mean values are calculated across the seven seasons (six for Riverina) from the General Linear Model using the evapotranspiration figures as co-variates; values in brackets are Fishers 5% LSD’s. The slopes are calculated from linear regressions between the evapotranspiration (independent variable) and the number of fungicides applied for each region (or all regions, designated Australia, see also Figure 5), values is brackets are the standard errors of the slopes, R2 and P values also relate to the regression analysis.

+ p < 0.1, * p < 0.05, ** P < 0.01, *** P < 0.001

Outline

  • Sample number – enterprise and block per region across seasons.
  • Number of actives per block (2 graphs)

    • Variety variation between seasons and regions
    • Variety variation between seasons and cultivars
  • Number sprays per block (tractor passes) (data not presented)

    • Variety variation between regions
    • Variety variation between seasons
  • Number of products used at once

    • Variety variation between seasons and regions
  • Timing of sprays (table) – variety, region, season (hope all aren’t significant or use Chardonnay)

    • First spray per season (date)
    • Spray season length (days)
    • Average spray interval (days)
    • First spray per season (growth stage)
    • Last spray per season (date)
    • Last spray per season (growth stage)
    • Proportion of sprays pre-flowering? – still under review (need a definitive reference)
    • Spread across season – graph?
  • Active ingredient/Mode of action used (table)

    • Contrast with S and timing by region (graph)
    • Immediate repeats
    • Repeats per season
  • Water rates within a region. – Do not include as not that interesting
  • Rates of sulphur for Powdery Mildew. – Do not include as not that interesting
  •  
  • Program response to weather (ETo – graph and table)

Stummer, B.E., Francis, I.L., Zanker, T., Lattey, K.a., and Scott, E.S. (2005) Effects of powdery mildew on the sensory properties and composition of Chardonnay juice and wine when grape sugar ripeness is standardised. Australian Journal of Grape and Wine Research 11, 66-76.

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