Efficacy of the antitranspirant Vapor Gard® under controlled & field conditions Darren Fahey Suzy Rogiers

Antitranspirants to manipulate grape production? Product performance in controlled environment and field experiments? Impacts to yield, grape & wine quality? In recent years a warming trend has resulted in earlier more compressed vintages impacting on winery logistics and resultant wines with higher alcohol. The aim of this work was to test the antitranspirant Vapor Gard in controlled and field conditions to see if the treatment could manipulate grape production with no detrimental impact on yield, grape and wine quality.

What are Anti T’s? Anti-T’s are generally used on crops to reduce water loss, cold desiccation, heat stress and drought stress. Vapor Gard® Active Constituent: 904.32 g/L di-1-p-MENTHENE Gatti et al 2016 – worked on Barbera Major findings – Antitranspirants were effective at slowing sugar accumulation while avoiding a concurrent delay in colour development. Limited studies undertaken on winegrapes in Australia. Vapor Gard is a water emulsifable concentrate, a terpenic polymer produced from pine or conifer resin The label claims suggest it is used to reduce water loss, cold desiccation, heat stress and drought stress. Italian researchers Gatti and others studied antitranspirants a few years ago on Barbera after observing a trend in earlier grape ripening. Their study across 2 vintages found when antitranspirants were applied at pre veraison or in combination with a pre flowering spray sugar accumulation was slowed without any impact on the accumulation of anthocyanins. While some trial work of antitranspirants has taken place in conjunction with sunscreen products, little published data exists on thier use in winegrapes in an Australia context.

Water Relations Source: If we think of water relations in winegrapes it is between fruit set and harvest where over 70% of annual water of vines is required during a season. Source:

Water Relations Water loss is controlled by varying the stomatal aperture Stomata have a dual role: 1) Photosynthesis- carbon dioxide (CO2) 2) Release oxygen (O2) and water (H2O) to the environment Stomata balance transpiration and prevent excessive water loss, whilst maintaining adequate photosynthesis for healthy growth. Therefore reducing transpiration especially in warm/hot climates may assist in maintaining berry and leaf integrity. Source:

Where should the antitranspirant be applied? Upper surface Lower surface So, where should antitranspirants be applied? In this study we wanted to see if the polymer being sprayed on was acting as a physical barrier or actually closing stomata, in which case it would need to be applied to the lower surface of the leaf, as that is where stomata are located Easier to achieve in the lab and less so in the field.

Transpiration (water loss) Photosynthesis (carbon gain) 2% VG was painted on the upper, lower or both leaf surfaces to better understand where it is most effective. Leaf transpiration (water loss) was not significantly reduced when applied to the upper surface of the leaf, but when applied to the lower surface transpiration was significantly lowered. Painting both surfaces reduced transpiration slightly more than only the lower surface- but this was not significant.

Stomatal conductance The reduction in transpiration and net assimilation was a direct effect of reduced stomatal conductance. However a cryoSEM study revealed that the antitranspirant did not alter stomatal guard cell function since stomatal aperture was not reduced in response to the treatment. Stomatal conductance was thus reduced simply by the blockage of the pore itself.

At what temperatures is the antitranspirant effective? Transpiration (water loss) Photosynthesis (carbon gain) In order to assess how effective VG is across a temperature range, potted vines were sprayed with 1% VG and ten days later they were moved into controlled environment chambers where the temperature was increased from 20 to 35 C over a four day period. Prior to moving the vines into the chambers there had been several heavy rain events and we were worried that the VG would have been washed away so two additional treatments were given to the vines once they were moved into the cabinets. These were a 1% dip and 2% dip of specific leaves on each plant. The 1% spray was effective at reducing leaf photosynthesis, transpiration and stomatal conductance at 20, 25, 30 and 35 °C despite several intervening heavy rain events between spraying and measurement . A 1% treatment on the morning prior to measurement was, however, even more effective across this temperature range showing that the rain did reduce the efficacy of the VG to some extent. 2% VG did not provide any significant additional benefit to the 1% treatment. Compared to untreated leaves, 1% VG reduced transpiration by 30% at 35 °C relative to untreated leaves. Even though photosynthesis was also reduced by the treatments but the instananeous transpiration efficiency was improved at 25 and 30C and the intrinsic transpiration efficiency was improved at 30 and 35C.

Is the antitranspirant effective on the bunches? It is obvious that VG has an effect on the leaves but we also wanted to know if it could reduce the transpiration of bunches themselves. This practical information will shed light on what part of the canopy to target when spraying. The transpiration of bunches decreases dramatically naturally as they develop from the peppercorn to pea size, veraison, 20 Brix and 25 Brix. This is mostly due to the waxes that develop over the surface of the berry and also due to the decrease in surface area to volume ratio. However we wanted to assess if transpiration could be reduced even further with VG.

Is the antitranspirant effective on the bunches? Fruit set We found that VG was effective at all stages of development. At the fruit set stage 2% was significantly more effective than 1% VG

What concentration is most effective? Peppercorn, pea size and veraison At the rest of the stages we went up to 3% VG. At the peppercorn stage 2% VG halved the rate of weight loss relative to the control but 3% di-1-p-menthene did not provide further protection At the pea size stage neither 2 or 3% was more effective but at veraison 3% was more effective.

What concentration is most effective? 20 and 25 °Brix 1 and 2% were effective at reducing weight loss at 20 Brix as well as at 25 °Brix. 3% Di-1-p-menthene was not able to curb weight loss significantly more than the 2% treatment.

Does the antitranspirant act on the bunchstem or the berries? The product had an effect on both the rachis and berries as evidenced by the prevention in weight loss from both these components.

What are the effects on bunch temperature? Just as in humans, transpiration in plants has the beneficial effects of cooling. When we reduce the ability of a leaf or a berry to transpire by coating it with a film, we may be resulting in significant tissue heating which may be detrimental to fruit composition.

What are the effects on bunch temperature? We assessed the effects of VG on berry temperature, under uniform illumination and little air turbulance and found that berries were 12-13 °C warmer than the air temperature (23.8 °C). Berries treated with the 2% VG were a further 0.9 °C warmer relative to the untreated berries. This may or may not be significant considering the more than greater 10 C rise in the control berries.

Does the antitranspirant alter cap fall or fruit set? Does it induce fruit abortion? Finally, 1% VG did not alter the onset of flowering or fruit set. Six days after spraying, the inflorescences had attained 83 ± 3% capfall while the control inflorescences had attained 87 ± 4% capfall (P=ns). Eleven days after spraying, the proportion of inflorescences that had reached the fruit set stage was also not altered (P=ns) at 64± 6% in the sprayed vines and 72 ± 8% in the control vines. 1% VG did not induce fruit abortion as there were no fruit aborted in either of the treatments

Summary – Controlled conditions Reduced transpiration of leaves and bunches 1% is very effective On leaves, it’s most effective at 30°C, but also still very effective at 35°C. Has to be applied to the lower surface of the leaves to be effective. Lost some effectiveness after rain. Did not promote fruit abortion Increases bunch temperature slightly

Field Trials Locations:Canberra, Griffith, Hilltops, Hunter, Mudgee, Orange & Tumbarumba Variety: Pinot Noir (2 sites) & Shiraz (7 sites) Vine Requirements: 4 Treatments x 12 vines x 5 replicates = 240 vines/site A fully randomised, replicated complete block trial design was established across 9 separate sites and 7 wine regions on Pinot Noir and Shiraz winegrapes. The 2017/18 would be the 2nd year of study on the Pinot Noir sites and the first year for Shiraz. Landholders pruned vines to uniformity and vine balance prior to the season commencing with all ongoing management throughout the vintage undertaken equally across the entire trial block. No landholder was asked to reduce any irrigations.

Applications VaporGard® @ 9.5L/Ha in 950- 2000L water/Ha (label rate) Applied as a 1% solution rate in water = 150ml/15L tank to canopy leaf and bunch structures. Timing = T2 @ pre flowering (PF) [EL 17], T3 @ pre veraison (PV) [EL 34] and T4 @ pre-flowering & pre-veraison (PF +PV) [EL 17 + EL 34]. Applications were put on according to label rates using a 15L, 4 mega pascal pressurised backpack spray unit. Vaporgard treatments were applied on visual assessment at pre flowering, pre veraison and a combined treatment at both pre-flowering & pre-veraison. Previous field trial work carried out in Italy used solution rates of 2 and 3 % on barbera and sangiovese.

Seasonal growing conditions Year Site no# Location *Long term mean rainfall Sept – March (mm) Vintage rain Sept –Harvest date (mm) *long term mean max temperature Sept –Mar (°C) Vintage mean max temperature 2018 1 Hunter Valley 502 267 27.2 29.1   2 Mudgee 447 218 26.4 28.3 3 Orange 542 377 21.9 23.9 4 & 5 Hilltops 359 335 27.9 6 Canberra 419 436 25.1 25.8 7 & 8 Griffith 237 117 28.2 30.3 9 Tumbarumba 514 406 23.7 25.5 Other than Canberra all trial sites were down on vintage rainfall against the long term means, it must be noted that the Hilltops Pinot Noir trial site is the only site dryland grown with all others supported by irrigation if required. Mean maximum temperatures were up by around 2 degrees Celsius across all the sites, demonstrating a dry hot season experienced by most across NSW wine growing regions. Meteorological data variables showing *long term means <15yrs to >130yrs for rainfall and temperature compared to vintage actuals across the trial period of 2018.*Source: BOM sites from 1-9 respectively 061260, 062101, 063254, 073138, 070351, 075041 & 072043.

Yield – all sites 2018 Overall in 2018 a significant increase in yield occurred with the use of VG at seven of the nine sites. In all VG treatments yield increased above the control at sites 1, 2, 3 and 9 with PV and PFPV significantly increased above the PF and control treatments at sites 4, 6 and 7. Overall where yield was significantly increased with a VG treatment above the control, increases ranged up from 18 to 30 percent with site 3 at Orange resulting in the highest percentage increase across all sites. Values with different letters on the same row are significantly different (p < 0.05)

°Brix – all sites 2018 Four of the nine sites in 2018 resulted in treatment differences with PFPV significantly lower than any other treatment at sites 3 and 7 at sites 4 and 9 it was the PV and PFPV equally reducing °Brix levels. The control and PF treatments were equally higher in readings across the same four sites. Values with different letters on the same row are significantly different (p < 0.05)

Anthocyanins – all sites 2018 Very little differences resulted in grape pH and TA differences across all sites. Three of the nine sites recorded equally significant reductions in anthocyanins with PV and PFPV treatments equally below the PF and control. Interestingly, the majority of Shiraz sites trended lower in PV and dual treatments of VG than the control both Pinot Noir sites trended the opposite way with increases occurring above the control in the same treatments. No Total phenolic differences resulted between any treatment occurred across all trial sites in 2018. Values with different letters on the same row are significantly different (p < 0.05)

Summary – Field conditions Significantly increased yield at 7 of the 9 sites. Significantly reduced °Brix at 4 of the 9 sites. Significantly reduced anthocyanins at 3 of the 9 sites. Effect on anthocyanins maybe varietal specific. Good ROI if fruit price is above $600/T.

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