|Application for bush and cane berry fruit crops
Dr Terry Mabbett*
Berry fruits from bush and cane crops are increasingly labelled as the ‘super foods’ for their rich content of vitamins, minerals and other health giving chemicals. But these high value horticultural crops, including raspberries, blackberries, blueberries and blackcurrants, are special in other ways too. They require the utmost care when passing along the rows with spray application equipment. As individual and often botanically unrelated species they suffer their own pest, disease and weed problems requiring custom-designed application both in timing and the targeting of spray. The industries which use them, whether they be supermarkets for fresh fruit or manufactures of juice and cordials, are especially sensitive to even the slightest transgression when it comes to pesticide residues. This collection of exacting requirements has led to development and use of some of highly innovative spray application equipment custom designed for temperate bush and cane berry fruit crops.
Blackcurrants are no exception. They are among the smallest of commercially grown fruit but pack one of the biggest punches in health giving constituents. Hugely rich in antioxidants and notably anthocyanins, imparting the unrivalled character and rich colour, blackcurrant is dubbed one of the ‘superfoods’ in today’s increasingly health conscious society.
The commercial crop is almost entirely sent for processing, demanding pest and disease free fruit with virtually nil chemical residues. These seemingly conflicting requirements place blackcurrant growers in the most difficult of situations, even by the exacting standards of highly sensitive horticulture as a whole. But United Kingdom (UK) growers have risen to the challenge with high yields of premium quality fruit using sound integrated crop and pest management systems. Chemical pesticides are only used when absolutely necessary and delivered by the least environmentally impacting application technology.
Blackcurrants are famed for their high vitamin C content (three times that of citrus) but the tiny purple fruit is very much a ‘dark horse’ when it comes to healthy eating. Blackcurrants are brimming with anthocyanins health promoting antioxidants which impart the deep purple colour to fruit and mop up potentially dangerous ‘free radicals’ in the body.
It is entirely fitting that the UK’s number one healthy-eating and drinking fruit is produced within environmentally sensitive growing systems offering protection for workers, consumers and wild plants and animals alike.
Pests and diseases of blackcurrant
For a rugged bush bearing tiny fruit Ribes nigra is troubled by more than its fair share of arthropod pests, diseases and weeds. Many are successfully managed using cultural control including resistant varieties from the ‘Ben’ series of cultivars bred by the Scottish Crop Research Institute. Breeders combined frost hardy germplasm from Scandinavia in traditionally early UK varieties to produce a range of high yielding varieties with increased fruit quality and the added bonus of frost resistance.
‘Ben Lomond’ (first in the series) was resistant to mildew when introduced in the 1970’s but is now highly susceptible and has been superseded by more modern varieties like ‘Ben Hope’ and ‘Ben Gairn’, released just eight years ago and pre-eminent in the UK. ‘Ben Hope’ and ‘Ben Gairn’ are regarded as ‘IPM’ (Integrated Pest Management) varieties. They have transformed blackcurrant crop protection and allowed growers to meet the single biggest pest and disease challenge in the industry, the blackcurrant gall mite (big bud mite) [Cecidophyopsis ribis] which lives in large and overgrown buds. Control measures are increasingly limited for this arachnid pest that was always difficult to kill by chemical spraying. The gall mite carries and transmits an even more damaging problem, the virus particle that causes ‘Reversion Disease’. Plants become sterile and fail to fruit. The disease may take hold and spread rapidly throughout the plantation with all ‘reverted’ bushes carrying no crop.
In addition to high yield and good flavour profile ‘Ben Hope’ offers considerable resistance to gall mite – up to thirty times higher than other mainstream varieties – while ‘Ben Gairn’ with its resistance to ‘Reversion Disease’ is extending the life expectancy of plantations threatened with this debilitating virus disease.
Few crops escape aphid attack and UK blackcurrants are no exception. Aphids on blackcurrants include Hyperomyzus lactucae (currant sowthistle aphid), Aphis grossulariae (gooseberry aphid), Rhopalosiphoninus ribesinus (currant stem aphid) and A. schneideri (permanent currant aphid). These are generally kept in check by a range of natural enemies, including coccinelid predators as adult and larval ladybirds, predatory hemipteran bugs like Orius species and Anthocoris nemorum (common flower bug) as well as parasitic wasps such as Aphidius matricariae which lays its eggs in the aphid host, and soldier beetles which can arrive in large numbers as if from nowhere. According to some growers Ben Hope has a degree of resistance to the currant sowthistle aphid and gooseberry aphid un-reported by the plant breeder.
Two spotted spider mite (Tetranychus urticae) numbers can build up rapidly in warm weather on the sheltered undersides of leaves but are normally suppressed by predatory mites of which Typhlodromus pyri and Amblyseius cucumeris are the most important.
But these and other arthropod pests including blackcurrant leaf midge (Dasineura tetansi), common green capsid (Lygocoris pabulinus), blackcurrant sawfly (Nematus offaciens), winter moth (Operopherta brumata) and fungal diseases like leaf spot (Pseudopeziza ribis), Botrytis (Botrytis cinerea) and white pine blister rust (Cronartium ribicola) may temporarily ‘escape’ natural and cultural control and require prompt but highly targeted and environmentally sensitive spraying.
Controlled Droplet Application
Micron Sprayers pioneered and developed CDA (Controlled Droplet Application) spraying. The company has a long history of working with UK blackcurrant growers, providing custom-designed equipment meeting the need for sensitive insect pest and disease control within the delicate ecological and environmental balance of the blackcurrant plantation. Growers throughout key blackcurrant producing areas such as Scotland, Kent and East Anglia use Micron’s equipment as well as growers in Herefordshire and Worcestershire right on Micron’s doorstep in Bromyard, Herefordshire.
Controlled Droplet Application provides growers with cost effective and targeted application. Strict control of droplet size distribution married with appropriate air assistance furnishes the good canopy penetration and coverage required for low volume control of foliar insect pests and diseases.
Micron’s Turbofan rotary atomiser is driven by a compact hydraulic motor and mounted in a protective cowl. The spray is delivered in a narrow range of droplet sizes appropriate to the target pest and the axial fan incorporated in the spray head produces a turbulent and swirling directed low-speed air beam to convey spray to the foliage. Foliage is simultaneously ruffled and disturbed to provide good penetration and even coverage of spray over all leaf, stem and fruit surfaces. This avoids the walling and shingling of the foliage seen when high-speed air jets are used. Directing this relatively low speed air accurately means that spray droplet losses outside the canopy can be minimised.
Edward Thompson, a well known blackcurrant grower from Ledbury in Herefordshire, is a big fan of CDA and the Turbofan. He uses self-propelled sprayers mounted with either 2 or 3 rows of 3 Turbofan heads targeted at bush crowns on each side of the inter-row, bringing air volumes together into the centre of the bush. According to Edward, “this arrangement removes all the air from the bush and creates the most fantastic turbulence, opening up the canopy for uniform distribution of spray droplets on the berries and leaves including the under-surface.”
“An even distribution of deposit is crucial with too much just as bad as not enough. Too little and there is insufficient control and too much puts the produce at risk. It is important not to create a concentration of spray on the fruit. The Turbofan gives excellent control of both arthropod pests and fungal diseases and enables reductions in pesticide usage. Furthermore it facilitates 12 m LERAP reductions in ‘Buffer Zone’ restrictions down to a minimum of 7 m for most pesticides without use of windbreaks.”
“Traditional orchard and vineyard sprayers are not correct for blackcurrant bushes”, says Edward. “Non targeted and too high speed air blasts lack the turbulence to get spray into the middle of the bush and instead shingle foliage, creating a wall which blocks canopy penetration. Apart from concerns as to the concentration of spray on exposed fruit, there are additional concerns relating to drift, and soil compaction when using much heavier sprayers using high volumes, but without the same widespread distribution of spray within the bush”.
“With LERAP considerations calling for 75% dose reduction in individual spray applications to maintain reasonable ‘Buffer Zones’, the Turbofan is a valuable aid to the whole concept of Integrated Crop Management and concern for the environment.”
Weed management in blackcurrants
Weed management in blackcurrants is also a delicate issue requiring sensitive balance between bush growth and development and maintenance of biodiversity. Biodiversity is not important purely for its own sake but also because many wild plants around blackcurrant fields provide shelter and habitats for natural enemies of blackcurrant pests. Adult vine weevils will damage leaf margins but the important damage is caused by the soil inhabiting larva stage with serious root damage and weakened bushes. Vine weevils are largely kept in check by predators, prominent of which both in size and activity are the predatory beetles from the carabid family, including the violet ground beetle (Carabus violaceous), strawberry seed beetle (Harpalus rufipes) and Nebria brevicollis. These important predators thrive under grass and blackcurrant growers specifically generate grass alleys, where these are compatible with the variety, between the rows and grass “beetle banks” at the field margins to encourage predator populations. Reduction and change in use of pesticides encourages beetles, worms and other expressions of biodiversity within the growing crop.
However, blackcurrants, like other fruit crops, suffer from a wide range of weeds. Some have the potential to grow tall and shade as well as compete for water and nutrients, while others like creeping thistle are invasive and difficult to eliminate once established. Dandelion, purple knotweed, shepherd’s purse, docks, mayweed, nettles and thistles will invade the crop given the opportunity.
Closely spaced blackcurrant bushes translate into hundreds of miles of inter-row where traditional heavy high volume sprayers can damage overhanging leaves and stems from untargeted herbicide spray and also cause soil compaction, damaging the roots. Shrouded CDA low volume sprayers offer a dual solution to these problems, controlling spray drift by use of rotary atomisers and covered spray heads and compaction by offering a lightweight low volume sprayer. Micron’s ‘Enviromist’ range of shrouded CDA herbicide sprayers offer:
Controlled droplet and dosage application through optimally sized spray droplets (produced by Micron rotary atomisers).
A shrouded (covered) system of spray heads to minimise any risk of spray drift
Significantly reduced spray volumes (down to as little as 12 litres/ha) compared with traditional high volume sprayers, allowing these sprayers to be mounted on ATVs as well as tractors.
The Enviromist range of spray units has something to satisfy the requirements of all growers:
The Undavina rolls around the plant stem on a delicate spring loaded breakaway mechanism providing a band spray right up to the plant. It is ideally suited for spraying over rugged terrain because the brush around the shroud permits covered spraying almost anywhere, even over small rocks and irrigation sprinklers.
The circular Spraydome is more rigid but still moves in a gentle, rolling effect around plant stems (and can be converted to the Undavina format).
The adjustable version of the Spraydome range, e.g. Spraydome 1524 has an adjustable width from 1.50 to 2.40 metres.
The Spraymiser range of units which are designed for centre-row weed control.
All of the Enviromist range is light enough for mounting onto ATVs as well as tractors.
Growers can get out and spray early even in excessively wet spring conditions and much reduced spray volume (as little as 12 litres/ha compared with 200 litres/ha or more typically used for high volume applications). CDA (which also implies controlled dosage application), together with Enviromist's 'roll around' design, avoid checks on crop growth caused by plant damage or soil compaction that are commonplace with less accurate and heavier sprayers.
Edward Thompson was an early convert to CDA weed control in blackcurrants, concerned at soil damage and compaction from heavy traditional high volume sprayers and convinced of the need to reduce the amount of chemicals used and minimise any risk of spray drift. He currently uses a variety of Enviromist units including Spraydome 600’s mounted on a six-wheeled John Deere ‘Gator’ and larger Spraydomes on a small lightweight tractor.
The practical benefits are considerable - more windows of spraying opportunity, quicker movement along the inter-rows and less down time and quicker turn around times (with significantly less time spent mixing and filling). Using just 25% of full dose rate will gain maximum reduction in buffer zone widths under LERAP (Local Environment Risk Assessment for Pesticides).
The strategy has certainly paid dividends for wildlife and biodiversity on Edward Thompson’s farm. Undulating fields of neatly tended blackcurrants growing in largely weed free conditions are bounded by grassy margins full of spring flowers like rose (red) campion, greater stitchwort, bluebells and white deadnettle, and all against a backdrop of ancient broadleaf woodland, contributing to biodiversity and rich habitats for natural enemies of insect and mite pests of blackcurrants.
Dr Terry Mabbett Consultants
Tel: +44 7976 602661
Further information and details on the spray application equipment described in this article can be obtained from:
Micron Sprayers Limited, Bromyard Industrial Estate, Bromyard, Herefordshire, HR7 4HS, United Kingdom. Tel. +44 (0) 1885 482397. Fax. +44 (0) 1885 483043.