Light solution for salad

According to Andy Lee, of Substratus Horticultural Consultancy, growing using assimilation lights requires a total mind shift, equivalent to that of moving from soil to substrate.

Dutch tomato growers are leading the way with an estimated five per cent of glasshouses (60 hectares) now fitted with assimilation lights. This is expected to double to 120ha by the end of 2005.

“Year-round production enables growers to capitalise on higher winter prices, and can promote more efficient use of energy per kilo of product,” said Lee. “While helping to achieve greater uniformity in production and quality, it can even out labour requirements.”

Supplementary light can enable growers to make more efficient use of other inputs, such as heat. Waste heat from the lights can also significantly reduce the proportion of heat sourced from the boiler.

However he warned: “There are cost implications, such as the increased energy usage and associated tax implications as well as the lights themselves. Approximate costs of a 10,000lux system are 35 euro/sqm, while moveable lights are 12 euro/sqm.”

Light pollution can also be an issue, in the Netherlands growers are restricted from using lighting between 8pm and midnight.

There are also crop management challenges. Tomato crops destined for production under assimilation lights are often planted in late summer when natural light levels are high.

“It is very easy for these crops to loose balance,” said Lee. “With the absence of fruits there are a lot of assimilates left for the growth of leaves and root. Special attention must be paid to crop management to prevent physiological quality issues such as blossom end rot on the initial trusses.”

In addition, there are other crop management challenges for the industry to address - not least IPM and pollination issues.

With low natural light levels, pollination can be difficult from November to January as bees become disorientated.

This is a particular problem in Finland, as double skinned polyhouses are traditionally used, which keep out what natural UV light there is - typically just 50 joules a day in December and January.

To help, it is advisable to close hives prior to the assimilation lights being switched off - this means the bees can enter the hive but not leave.

On the pest front, while the pressure from outside is vastly reduced during winter, with the minimum of breaks between crops pests can carry through to the winter crop.

Different growing techniques can affect pest build up and also the establishment of beneficials. With interplanting, pests will readily migrate and be attracted from surrounding crops to the new young plants. It is therefore important pests, such as whitefly, are well controlled on surrounding crops.

Phytoseiulus may not perform as well in lit crops where the head of the plants are near to lights due to the lower humidity. There is also the issue of lights attracting moths into the crop in September.

Substratus estimates that in Finland 20ha of tomatoes are being produced in winter, using 20,000-30,000lux supplementary lights.

According to Lee, Dutch tomato growers are using 10,000-15,000lux light for 2,500-3,000 hours per year. “The lights are programmed to come on and off in stages,” he said. “With a natural light intensity of 200 to 300W growers use 5,000lux. With the heads of the plants generally two metres from the lamps, deep reflectors create uniformity across the glasshouse.”

Early indications in Dutch trials involving moveable 25,000lux lights, capable of travelling 80m in 27 minutes and delivering 2,500lux/sqm, suggest the crop is brought forward by four to five weeks.

When it comes to cucumbers, according to Lee, the major driving force changing production in northern Europe is to improve fruit quality by reducing the amount of class II fruit from 13 per cent to four per cent.

In Holland, moveable crop wires enable growers to produce high wire crops - hence 100 per cent stem fruit, without incurring large labour costs.

When the crop requires layering or picking it is simply lowered, worked, and then raised again. These systems require tall greenhouses, typically 5.5m to the gutter. Preliminary tests proved so successful that 600W assimilation lights have now been introduced providing 10,000lux to allow production throughout the whole of winter.

In Finland, where double skin polythene houses are the norm, Substratus estimate 27ha of lights are now being used in cucumber production.

“The crops are typically lit for 20 hours per day, using 400W lamps because the houses are too low for 600W lamps,” said Lee. “Ventura, Cumulus and Aviance are grown on high wire systems at planting densities of 2.5 to 2.7 plants per square metre yielding 2.5 to 3.0 kg/sqm/week.”

Systems using 30,000lux typically use interlights where 15,000lux is suspended over the crop, and 15,000lux in the middle canopy layer. Finnish growers also use interplanting techniques to stay in continuous production using Grodan Master ‘Stubby slabs’ (50x24x10cm). Spaced at intervals along the hanging gutters, new slabs can be inserted for each crop.

This limits the potential for Pythium, as the cucumber plants produce a tremendous amount of root. The crops grow rapidly and novel layering systems are adopted to save labour. With outside winter temperatures plummeting to minus 20-30°C, venting is not an option.

“The heat generated by a system using 30,000lux is massive,” said Andy Lee. “Typical 24 hour temperatures are 23-25°C. The crops soon loose balance and become too generative, hence four to five crops are grown per year. However, on the positive side at minus 20°C there is no outside pest pressure.”

BCP is a sponsor of the year-round cucumber research project at Stockbridge Technology Centre (STC) in North Yorkshire.

The glasshouse is fitted with Hortilux HS-Remote luminaries - with 600W high-pressure sodium lamps.

Although capable of delivering 20,000lux, trials suggest 10,000lux is sufficient to deliver the desired yield target.

In the first year, when light levels fell below 300W/sqm the lights were switched on - for a maximum of 18 hours a day.

The first crop, planted week 45 of

2003 yielded 73 cucumbers/sqm by the end of February - a period when most conventional UK growers are out of production. By the end of the second crop in June total yields had hit 200 fruit/sqm.

By the end of the third crop the final

yield was 315 cucumbers/sqm - exceeding the target of 300 by a very comfortable margin.

“The Aviance crop is layered in a similar way to tomatoes enabling more light to reach young active foliage,” said Dr Rob Jacobson of the STC. “Using similar de-leafing strategies, the oldest leaves in the crop are three weeks.

“Foliar pests and disease have been less troublesome than anticipated. Pests barely have time to complete their life cycles.

“Good control was achieved using routine applications of beneficials to control thrips, whitefly, spider mite and leafhopper.”

Phytoseiulus gave good spider mite control with a single hot spot developing mid-summer which was effectively controlled using BCP’s soft pesticide Eradicoat.

Good thrips control was achieved with three introductions of Amblyseius sachets to the first crop made at fortnightly intervals, at one every third plant.

“With the plants touching from the beginning, the predator was in evidence throughout the crop.

A similar strategy was used at the start of the second and third crops, and then repeated after 8-9 weeks, which was the half way stage in each case. Once again, the approach successfully suppressed the pest’s development.

“With the de-leafing strategy, it is borderline as to whether whitefly can complete their lifecycle while Encarsia has little chance,” said Jacobson.

“We introduced Encarsia routinely as a prophylactic with the adults stinging out any young scales. We did experience greater whitefly pressure in the second crop so doubled the Encarsia introductions for three weeks, which successfully nipped it in the bud.”

While Aviance is mildew tolerant, Jacobson and his team saw very little foliar disease in general. “We only sprayed twice - more as a preventative rather than curative due to diseases possibly spreading from other crops on the STC site,” he says.

Jacobson is keen to point out that while the project is large by experimental standards, 1000sqm is small in commercial terms so the crop does receive high attention to detail.

In summary, supplementary light offers UK growers the potential to satisfy demand from retailers for uninterrupted supplies of good quality, traceable homegrown produce.

However, there are still many unknowns. Projects such as the on-going four-year STC project are playing an important role in helping to determine optimum production levels in relation to energy use and other inputs including IPM.

STC and the Cucumber Growers’ Association are grateful to the following companies who have contributed to the infrastructure, crop production and marketing: BCP, Cavegates Nursery, CMW, Derek Hargreaves Horticultural Consultancy, Ecotech, FEC Services, Green Meteor, Grodan, HDC, Hortilux Schreder, Leen Huisman, Ludvig Svensson, Marks and Spencer, Melrow Salads, Plant Raisers, Priva, Rijk Zwaan, Syngenta Bioline.

COOL CONDITIONS BOOST SPANISH

Sales of winter tomatoes from the Canary Islands and Spain have been slow so far this season and prices have increased dramatically, said Steve Cornwell, Sales & Procurement Director of Spania Fresh Produce.

“There are a number of important factors that have contributed to this situation,” he said. “In general less volume was planted this year, and the crops were struggling a little after early planting throughout hot weather.”

He said the later fall in temperatures meant that the tomato plants were now yielding at a slow pace. “The market has noted the situation and reacted with a higher price level than last year.

“There is a big diversification in variety types now, in general, but they are all suffering from the same conditions, which is keeping the market starved of volume.

“We at Spania Fresh have some new varieties, unknown to the UK but very popular on Spanish dining tables.”

These are the Raff tomato, Camone and Kumato, said Cornwell. “They are grown in the Mazzaron area and the flavour is a new eating experience. The Camone’s colour is green stripes, with a red ripening from the centre.It’s like a starter meal on it’s own.”

He estimates these new tomato varieties will become prominent players in the UK market in the near future.

“Cucumber trade has been more steady, with more cues planted in the Motril/Carchuna areas, but there is less cherry tomatoes.

“Prices have stayed constant and demand has been quite good. The new year will see a sudden increase in value as crops are slowing down with the colder weather and the January and February trade will be good.”

He said cherry tomatoes and other vine type tomatoes will be expensive in the new year through a change of planting patterns. Meanwhile, capsicums will be shorter and prices will improve, he added.

RED BARON SUPREMACY CHALLENGED

Red onions are proving increasingly popular with consumers, particularly when it comes to salads.

As a result, scientists with NIAB, the Cambridge based leading plant science company, is running trials on 10 new varieties to allow growers to keep up with the increased demand.

Over the past 25 years, NIAB has only conducted field trials on five varieties of red onions, but this year, the number has doubled due to consumer demand being fuelled by foodservice and television cookery programmes.

The dominant variety over the past 15 years has been Red Baron, but breeders have been working hard to create modern hybrids to challenge the varieties supremacy.

According to NIAB, red onions now represent around 20 per cent of the UK onion crop. Three years ago, volumes stood at around 35,000 tonnes, last year it rose to 41,000t and this year it has topped 50,000t.

To meet the growing market for the crop, the group has, for the last three years, been testing Nickersons Red Pearl and Bejo’s Hyred. However, this year 10 red varieties have been sown in trials.

These new varieties include Red Spark, BGS 185 and Red Fort from Bejo, Red Kite from Seminis, Romy from Agriseed, Kamal from Steve Howe/Advanta as well as two Australian-bred varieties, Oaklands Red and Red Marksman from ProVeg.

The results of the first year trials, funded by the Horticulture Development Council and the seed companies, has shown that BGS 185 is the earliest variety to mature, a few days before Red Baron.

But while they looked good in the field, the bulbs appeared to be a little pale. NIAB said it was now waiting to see next year’s crop to check the colour is sufficiently red.

Red Spark, which matured five days later than Red Baron, are a slightly darker colour and a more elongated shape.

Red Kite arrived at the same time, but had a lower yield due to its propensity to bolt and produced a lot of double bulbs.

The slightly elongated Red Fort was the deepest red of all the varieties and matured eight days later than Red Baron, the same time as Red Pearl, which is flatter in shape.

Kamal proved to be a successful early mid-season variety with an average yield of smallish bulbs and a good colour while Romy, an open pollinated variety, matured around ten days after Red Baron, with an average yield of round, dark red bulbs.

The two Australian varieties, unfortunately, did not adapt to the UK conditions and bolted badly.

Mike Day, consultant with NIAB, said: “In all my years at NIAB, I have never seen such a massive demand for new red onion varieties.

“Over the last 25 years, we have seen no more than five varieties. But in the last year this has grown to 10, reflecting the increase in consumer demand.

“This year, the new varieties had their work cut out, competing with Red Baron, which delivered a particularly good harvest. It is the highest yielding variety, but it lacks uniformity of shape.”