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Use foliar nutrition and biostimulants to minimise frost losses – Vineyard Magazine – Chris Cooper, Rob Saunders

After May frosts damaged vines in many parts of the country, Chris Cooper and Rob Saunders examine how foliar nutrition and biostimulants could help crops ...

Growing fruit, particularly grapes, in a cool climate such as the UK is not without its challenges. The late frost in May, the latest in decades, damaged vines to varying degrees dependant on site, cultivar and frost protection measures deployed.

Those that managed to get through with little damage to primary flowers could be set for an early harvest, while those who had the primaries knocked out must push secondary and tertiary buds into action to throw out flowers and set a reasonable crop.

Growers with intermediate damage must choose between selective early bunch-thinning to even-up ripening, or, where the proportion of crop arising from secondary buds is small, it could be retained to contribute acidity alongside a main crop that is allowed to fully mature.

This second strategy requires a little luck in a sunny autumn, alongside robust botrytis protection. Either way, any damage to inflorescences developing from primary buds will inevitably hit yields, as regrowth from secondary buds inherently only produces 50-70% of the full crop, with growth now set back two to three weeks.

Rob Saunders

Much depends on the weather over coming months, but as that is beyond growers’ control, the focus must be on targeted agronomy to maximise inflorescence development from whichever bud it comes, whilst not compromising bud and cane growth for next season’s crop.

Foliar nutrition and biostimulants are key tools for this, providing a wide range of nutrients, hormones, amino acids and other biological compounds to promote recovery and renewal.

Hopefully all growers that experienced frost damage will have applied their first application to kick-start regrowth, but it is essential to maintain momentum. In many cases it will be necessary to repeat applications on a monthly, fortnightly, 10-day, or even weekly basis, depending on crop requirements, strength of regrowth and products used.

Chris Cooper

Many biostimulant options are available so tailor product choice carefully. Early application of a combined foliar fertiliser and biostimulant product, (such as Megafol or a seaweed extract as in Kelpak or Maxicrop) has worked well for many especially when alternated with the Cultigrow CBL plus Phosphite mix.

Glycine-betaine found in products such as Maxicrop or Folwin (from Lallemand) will help overcome the abiotic stress vines are under and promote rapid bud development. If the weather remains kind it is surprising what growers can achieve by the end of the season.

For those lucky enough to have experienced little damage, Lallemand also produces Pinot Pro-flowering which aims to promote fruit set, reducing millerandage in specific varieties (Pinot and Chardonnay) which are notorious for uneven development within the bunches. It has been shown that a timely application of this naturally derived product will promote a more even set.

As we head into flowering, it is important to have a well-planned nutrition programme using advisor and grower knowledge to avoid any sub-clinical nutrient shortages. Leaf analysis around this point is very helpful, although we accept in some cases flowering may now be in July.

An important part of the nutrition strategy is to apply calcium through flowering and again at early berry formation, to guard against Early Bunch Stem Necrosis (EBSN), a physiological disorder associated with a magnesium, calcium and nitrogen imbalance. Although not widespread every year, it can be extremely damaging, with yield losses of 50% reported in the past, and we are trying to avoid further yield losses this year. Boron will help pollen tube germination, which will assist with fruit set, although take care with tank mixes as boron is not compatible with some fungicide formulations.

By the end of July most growers will have an idea of likely crop yields come autumn, and in consultation with their advisor will adapt programmes to suit.

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