Watch for nutrient issues after dry start to spring – Vineyard
An exceptionally dry March and April may have kept down early disease pressure, but it could pose other challenges, as Hutchinsons agronomist Rob Saunders explains. ...
The start to the 2025 vineyard season has certainly been a welcome contrast to previous years, with fine, dry weather making for a comparatively easy time in terms of early disease control – at the time of writing at least.
And while mature vines with deep root systems will be better placed to tolerate the lack of rain, further dry weather could see some nutrient issues starting to appear, particularly in young vines, less than three to four years old, with less well developed root systems.
Older vines may not escape completely though, as a large proportion of nutrients are absorbed from the upper aerobic part of the soil profile, which is most prone to drying out, so there may be important distinctions between drought tolerance and nutrient resilience.
There are three key nutrients to watch: magnesium deficiency is a particular risk on SO4 rootstocks, which are known to have a poor ability to access magnesium from the soil. Iron is another nutrient that young vines may struggle to access in dry soils, as is phosphate.
The best way to determine nutrient requirements in any vine, young or mature, is with petiole sampling at early flowering, the results from which can be used to determine the most appropriate response.
Care is needed when interpreting results, as there can be some ambiguity with published guideline levels for specific nutrients in vines. Also recognise that absolute values cannot be considered in isolation, as the ratio of nutrients is important too. We have seen cases in the past where sampling showed no deficiencies in absolute nutrient levels, yet vines were still struggling, due to an imbalance in a specific ratio; such as having too much nitrogen relative to the level of micronutrients, for example.
Addressing deficiencies
If petiole analysis reveals an urgent need for certain nutrients, foliar nutrition in metalosate form has been shown to be a quick way to get nutrients into plants. Mineral nutrients are chelated with amino acids, which protects them from adverse interactions and improves absorption and translocation compared with more traditional foliar options.
A wide range of nutrients are now available in metalosate form, including multi-nutrient products, and single nutrients, such as iron metalosate, which is a go-to option given its improved availability over EDTA chelate forms.
Tackle powdery mildew early
It remains to be seen how the weather goes over coming weeks, but if conditions are conducive to powdery mildew (i.e. warm and humid), early action could be worthwhile, rather than waiting until we get into summer.
Even relatively small amounts of powdery mildew infection on embryonic berries can cause surface micro-cracking, which will predispose grapes to Botrytis. It can therefore be a mistake not to protect inflorescences with an appropriate fungicide at this stage.
Kresoxim-methyl is a good option at early flowering, as it also offers phomopsis protection, while if conditions are very conducive to powdery mildew, then cyflufenamid brings some additional vapour activity to improve coverage. In wetter situations, mefentrifluconazole may be preferred given its activity on both powdery mildew and anthracnose.
To get the maximum value from any product, the aim is to ‘layer value’ into spray programmes, by understanding the spectrum of activity of the materials available and identifying which best suit specific situations, so speak to your agronomist about the options.
New downy mildew controls
As discussed in last month’s issue, the past couple of years have seen real challenges with downy mildew control, due to high disease pressure in wet seasons, and a lack of approved products. It is therefore welcome to see a new option for this year, in the form of Privest (ametoctradin + potassium phosphonates), which is said to be particularly useful in protecting embryonic flowers and young fruit.
Additionally, it is hoped an extension of authorisation for minor use (EAMU) will soon be granted for the use of metalaxyl, and it is also anticipated that folpet will be approved for use in vines at some point this season, potentially providing some useful extra options for controlling this key disease.
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