Good things in small packages

B: Boron improves flowering and fruit set, as well as helping to boost the ripening process and also has a positive effect on berry size and the sugar levels they contain.

• A boron deficiency is a serious matter, visible through small bunches with only a few set berries, most being shrivelled and seedless. It is known as millerandage or, the disarmingly charming term ‘pumpkin and pea’. A lack of boron may also be visible through chlorosis around the outside of the leaf, which may turn to a red-brown colour before the leaves die off. The slow growth of shoots with short internodes, putting off large numbers of lateral shoots, may also give a visual clue.
• A deficiency can be exacerbated by either highly acidic or alkaline soil. Sandy soils are also particularly prone as boron leaches very easily. High levels of nitrogen or calcium are also warning flags to watch out for.
• A foliar application of boron can take place two or three weeks before bloom.

Mn: Manganese combats chlorosis, allowing the vine to develop healthy green foliage. A healthy green canopy will lead to better berry development and ultimately an improved yield.

• Manganese deficiency is visible through yellow interveinal chlorosis, while the fine veins stay deep green. These leaves will also be smaller in size.
• Sandy soils, organic soils and soils with a high pH may be particularly problematic when it comes to managing manganese levels.
• If a deficiency is discovered, manganese can be applied via a manganese sulfate foliar application sprayed for immediate effect. It is not recommended to apply treatments directly to the soil, particularly where pH is high or soil contains a high proportion of organic matter as they will rapidly fix the manganese.

Fe: Iron plays a role in chlorophyll formation and thereby supports early leaf production and the development of healthy green foliage. It can also help berry development and lead to increased sugar levels in the grapes

• Visible symptoms of an iron deficiency will begin on the youngest leaves, with yellow interveinal chlorosis, most severely faded around the edges. A very severe deficiency will also show up on older leaves and even shoots.
• A deficiency caused by a lack of iron in the soil is rare, but iron is less available in calcareous soils where the pH is high and calcium carbonate locks the micronutrient away. This is known as lime-induced chlorosis. Growers with these conditions will need to use rootstocks suited to the soil type.
• Foliar sprays of iron chelates are recommended for correcting iron deficiencies in vines. Direct soil applications of inorganic iron sources do not tend to be effective.

The direct application of micronutrients is an ongoing part of vineyard management. It can be a more problematic issue for organic or biodynamic properties where there are restrictions on what substances and products are permitted for use. The Soil Association and Demeter have detailed guidelines on what can be applied within their certification standards, although this is quite heavily restricted in terms of foliar applications.

For vineyard managers who are able to use standard micronutrient applications, there are a number of different micronutrient delivery technologies available. Drenches apply the micronutrients to the soil around the base of the vines. They can be effective for addressing soil deficiencies and providing a slow release over time. Controlled-release fertilisers are granular products that provide a sustained supply of micronutrients across the whole growing season. Similarly, soil amendments like compost and biochar can improve soil structure and fertility in the longer term to improve the vines’ access to nutrients.

One of the most commonly found methods of application is foliar sprays. By spraying directly onto the leaves of the grapevine deficiencies can be corrected. The micronutrients are quickly absorbed into the plant which can provide rapid improvement.

Even the best equipment can do a bad job if it hasn’t been set up properly. Our top tips for getting the most from your sprayer are:

• Time your spraying to avoid rain or high winds. Remember that drift will be lower with coarser sprays even though you sacrifice a degree of coverage.
• Calibrate your sprayer to check that the coverage is even and to find that balance between coarse and fine.
• Target the canopy of one row only per pass for the best efficiency and efficacy.
• Consider an adjuvant to help with the spread and uptake of droplets, with the added benefit of reducing the amount of water required overall.
• Vitifruit supplies many sprayers from different manufacturers that will meet the needs of vineyards according to their size, budget and the technical ability of the operator. A basic system starts in the region of £3,000. Something with significantly more bells and whistles will set you back £40,000 or so. Much of this machinery has been tried and tested in UK vineyards over several decades, so it is accepted as the “standard kit”. However, there are some new technological innovations in the area.

“There are two principal ways to apply chemicals onto vines using a spray,” explains David Sayell of Vitifruit. “Either by traditional nozzles or by specialised air shear nozzles, where the spray droplets are given an electrostatic charge.

“The droplets are of a very specific size and thanks to the electrostatic charge it enables the chemicals to bond to the leaf surfaces and berries exceptionally well. Due to its efficiency, the spray rates and litres per hectare can be significantly reduced enabling more efficient use of tractor and driver time with more hectares sprayed per tank load. The electrostatic sprayers are sold in big numbers around the world where water is a precious resource and chemical costs have to be minimised.”

Micronutrients are essential not just for the successful development of grapes, but also for the flavour and aroma of the finished product. The specifics of this can vary depending on the grape variety, growing conditions and winemaking techniques. In general terms though, it may be observed that zinc is essential for the synthesis of several aromatic compounds including terpenes and thiols. A zinc deficiency may result in a wine with reduced aroma and complexity. A lack of manganese or iron can result in decreased colour intensity in red wines. As well as impacting berry size and yield, boron deficiency may produce wines with a decreased flavour intensity.

As with all things, balance is the key. Excess levels of micronutrients can wreak their own havoc on wine quality. Too much and you may end up with an unpleasant metallic, astringent or bitter flavours. Too much zinc can result in high acidity levels that may be difficult to manage. High manganese or boron levels have been seen to contribute to the development of off-flavours, particularly in white wines. Excess levels of iron or copper can also contribute to the oxidative degradation of the wine, which reduces the aroma intensity and the stability of the colour. Proof that you can have too much of a good thing.

Research has suggested that the analysis of micronutrients could also be useful in the fight against counterfeit wine. A 2017 study in Brazil showed “that it is possible, based on the boron isotopic ratio, to differentiate Brazilian red wines from Chilean, Italian and Portuguese red wine.” The study was even able to identify differences in boron concentrations between the Southern and the North-Eastern Brazilian wine regions, suggesting the possibility in the future of developing “a fingerprint for each wine-producing area of the country.”

This is another tool, along with other new technologies like fluorescence spectroscopy, that are being developed to continue the global battle against wine forgery. But of course, you have to open the bottle first!