Achieving best results from vineyard sprays requires far more than just selecting the right product, explains Hutchinsons agronomist, Will Robinson.
Research by Syngenta for air-assisted sprayers in vines, top fruit and other horticultural crops, suggests correct application accounts for around half of overall efficacy, with product choice making up the remainder.
This is perhaps not surprising when we consider that a dose rate of, for example, 100 g per ha, equates to just 0.01 g of active ingredient per m2. Given the size of canopies in the middle of the season, a very small amount of active has to do a lot of work, so we need to give it the best chance of hitting its target and doing its job.
The same research highlights three main areas to focus on, namely ‘mechanical’ issues (typically 20% of lost efficacy), poor timing/weather (20%), and other ‘fine tuning’ (10%).
Mechanical issues
This covers various aspects, from correct tank agitation and fan speed, to speed of travel, direction of airflow from the sprayer, and potential ‘spray shadows’.
Air-assisted sprayers typically blow air clockwise, and if not setup correctly, the left-hand side can potentially be sprayed higher than thought, with more spray than expected lower down on the right-hand side.
The simplest way to check airflow trajectory is with the ribbon test, where lengths of ribbon are attached to air outlets before running the fan at full speed.
Air-assisted sprayers typically produce a ‘V-shaped’ spray pattern to each side, which should touch, but not overlap on each pass. Sometimes, where rows are tight and canes stick out into the row, leaves can intercept more spray and create a ‘spray shadow’ on the canopy behind.
Water-sensitive paper attached at different heights in the canopy can be a good indicator of spray coverage, as can adding a blue, food-grade dye to the tank. This easily washes off and provides a very visual indication of spray shadows, misses, or overlaps.
Spray penetration can be a particular challenge in dense canopies, so good canopy management helps improve efficacy. Modern sprayers often allow operators to adjust fan speed according to canopy height and density, whereas for many older PTO-driven sprayers, the fan is either ‘on’ or ‘off’.
Timing and weather
Applying sprays at the correct timing and in optimum conditions is crucial; growth stage, temperature, humidity, rainfall, and wind speed, all need considering.
Windspeed is perhaps the most important factor, both for ensuring application effectiveness, and minimising any risks to the surrounding environment. Nozzle choice and other ‘fine tuning’ can help mitigate some risks though (see below).
Many products are less effective in colder conditions, while volatilisation and scorch are potential risks in warm/hot weather, especially when applied in a fine spray. Sulphur in particular can be quite a ‘hot’ product, with a risk of scorch if applied when conditions are too warm.
However, it should be noted that some products use an element of volatilisation to improve coverage, so always check label requirements carefully.
Avoid spraying if rain is forecast during or immediately after application, as it risks washing product off before it has a chance to work.
Fine tuning
The final 10% of efficacy depends on ‘fine tuning’ decisions around nozzle choice, droplet size, water volumes, formulation, etc, to ensure everything is right for the specific product(s) and situation.
In general, a coarse spray will help reduce drift, but coverage may not be as good as a fine spray with smaller droplets. Air inclusion nozzles help mitigate this, by mixing air with pressurised fluid and creating a larger, air-filled droplet that is less prone to drift, and bursts on impact to improve coverage.
Again, always check label requirements for individual products, as some may specify certain nozzles to be used, such as LERAP low-drift nozzles.
Finally, stay up to date with National Register of Sprayer Operators (NRoSO) best practice and calibrate your sprayer regularly, to ensure equipment is delivering what it should. As a minimum, calibration should be done at the start of each season, and whenever nozzles are changed.
Herbicide applications
Read specific advice on herbicide applications in our January 2026 issue:
www.vineyardmagazine.co.uk/agronomy/simple-steps-to-avoid-herbicide-issues/
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