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aubergine

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Purple Pride will be offering aubergines grown under assimilation lighting starting this week. It is expected that over 100,000 kg of aubergines will be harvested this winter at Purple Pride’s cultivation site in Dinteloord, where a total surface area of 7000 m2 is dedicated to growing aubergines under assimilation lighting. Until recently, the only aubergines available during the winter season in the Netherlands were imported from Spain.

After three years of testing, Purple Pride now believes that the time is ripe to officially bring aubergines grown under assimilation lighting to the market. The fact that this took three years demonstrates that the growers’ collective did a lot of research before coming to this decision. Grower Peter de Jong: “We noticed that more and more of our clients were asking for Purple Pride aubergines outside of the regular season. There is a demand for locally grown products. However, the Spanish alternative is not always reliable in terms of availability and quality.”

Sustainably grown

Normally speaking, the aubergine season in the Netherlands runs from late February to mid-November. To respond to the production hiatus, aubergines are imported from Spain. De Jong: “We are convinced that there is sufficient demand for a product that distinguishes itself from the conventional variety in addition to the volume obtained from Spain. In addition to quality, our customers attach considerable value to sustainable production methods. We limit our water consumption to the absolute minimum, for example, and use biological crop protection methods.”

Aubergine brand

Purple Pride has been dedicated to growing high-quality aubergines on Dutch soil since 1996. With a harvest of over 20 million kilos of aubergines each year, grown at five cultivation sites, the growers’ collective has grown into north-western Europe’s largest aubergine brand. Purple Pride therefore makes every effort to increase the consumption of aubergines and to turn this fruit into one of the most highly valued culinary ingredients available. The sale and marketing of Purple Pride aubergines is in the hands of DOOR Partners BV.

Source/photo: Purple Pride/DOOR Partners BV.

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Paul Jeannet, farm manager of the UrbanFarmers rooftop greenhouse in The Hague, has used the Qlipr system for three months in four different crops: ‘It’s very easy to use, once you get used to it. It allows us to save time and - this is the biggest advantage in my opinion - we can reuse the clips after every crop cycle. We can easily separate the clips from the plants and compost the plants, because there are no strings or plastic clips left in it. Nothing is wasted.’

The Qlipr system fits right into the UrbanFarmers philosophy, which is based on creating added value and minimizing waste. At the UF002 farm in The Hague, consisting of a greenhouse with a surface area of 1,000 m2 on top of a former office building and a Tilapia fish farm, that philosophy has been taken into practice. The waste water of the fish tanks is turned into nutrients for the plants in the greenhouse. In the greenhouse, different varieties of lettuce, tomatoes, cucumbers, sweet peppers and aubergines grow in a hydroponic system. The water that is not used by the plants is purified and pumped back to the fish farm, which reduces overall water usage by 80%. Pesticides are forbidden; only biological plant protection methods are allowed. The products are sold to customers in the region, to minimise food miles. ‘We grow fresher, tastier and healthier products, as close to our customers as possible. And we minimise waste,’ Paul Jeannet explains.

The fresh revolution

Paul Jeannet (24) started working for Urban Farmers one year ago, after an internship at UrbanFarmers’ first farm (UF001) in Basel. He studied biological agriculture in Switzerland, before he joined ‘the fresh revolution’. ‘At first we were only growing lettuce and tomatoes. When our gastronomy partners told us that they would prefer more diversity, we took out some of the tomatoes and put in cucumbers, aubergines and sweet peppers instead, and several different varieties of tomatoes. We kept the lettuce section.’

It is quite different from the normal plastic clip we were using, but once you get used to it is very easy to use.

Six months ago Paul got in touch with Cor Pellikaan and became interested in the Qlipr system. ‘We wanted to give it a try to see if it would work in different crops. Three months ago we started using the system in tomatoes, cucumbers, sweet peppers and aubergines. As it turned out, the system is quite easy to use: we take the lower clip and place it on top and we lower the plant at the same time. It is quite different from the normal plastic clip we were using, but once you get used to it is very easy to use.’ The lowering schedule is once a week for tomatoes, three times every two weeks for cucumbers and once every two weeks for sweet peppers and aubergines.

Pilot project

Cor Pellikaan, the inventor of the Qlipr system, needed a pilot project to test his clips on sweet peppers and aubergines. Until three months ago, the system - which he invented in 1996 - was only used by growers of tomatoes and cucumbers worldwide. The system consists of a crop hook (1.40 meters long) and two clips. Halfway through the plants’ development, extra crop wires are needed with which to fix the crop hooks into place.

It will save labour, because you can de-leaf, remove shoots, prune and lower the plants in one go.

The main advantages of the system are, according to Pellikaan: ‘It’s very simple to use. Everybody can work with it. It will save labour, because you can de-leaf, remove shoots, prune and lower the plants in one go. This is also better for plant health, because there is less chance of damage.’ Paul Jeannet confirms that he saves up to six hours a week in the rooftop greenhouse because he uses the Qlipr system instead of regular plastic clips.

Durability

The main advantage of the Qlipr system is its durability, says Pellikaan. ‘My first client bought them 18 years ago and he is still using the same clips. Of course, you have to disinfect them at the end of every crop cycle, but that is very easy. You can use steam, chemicals or pasteurization. I recommend the latter, after two years of thoroughly testing this method. Just put the clips in a box on a trolley and cover it up with a canvas. Heat up four pipes to 60°C under it for three days. Works perfectly.’

Thanks to the Qlipr system neither plastic string nor clips are left on the plants after each crop cycle.

Paul says this is a big advantage too, but there is more. Thanks to the Qlipr system neither plastic string nor clips are left on the plants after each crop cycle. ‘So we don’t have to throw away our plants, but we can shred them for composting. It also makes it much easier for us to get rid of the plant material, because we have to transport everything via the lift.’

Qlipr versus traditional clips

How many clips are needed to bear the weight of the plants? ‘At the start of the season one clip will suffice. You attach it at 40 cm below the head of the plant. When the plants get heavier you will need to add a second clip, Cor Pellikaan explains. A new item in the Qlipr product range is the double-stop crop hook of 1.40 meters with two stoppers: one at 50 cm and one at the bottom of the hook. This makes it possible to use the same hook for tomatoes as well as cucumbers.

You buy it once and then you can use it every year.

The investment in the Qlipr system is higher than with traditional plastic clips, but they will last a lifetime, Cor says. ‘Also, you don’t need to buy expensive trolleys with hydraulic platforms, because the plant tips grow at a height of 160 cm. Therefore, cheap trolleys will suffice. In most cases this will save you enough money to buy Qlipr clips.’
Paul Jeannet has become a fan of the Qlipr system rather quickly: ‘Cutting leaves has become more enjoyable. We no longer have a plastic string or plastic clips at the bottom of the plant holding the leaves together. Only two clips at the head of the plant.’ Would he recommend this system to other growers? ‘Yes! It is a really interesting system to work with; you buy it once and then you can use it every year.’

Future developments

Pellikaan thinks the Qlipr system will also benefit growers in the future. He is working on a mechanical system to pollinate crops without the use of bumblebees. It has been tested thoroughly and he expects to launch it this year. He is also working on a robot that can harvest and de-leaf tomatoes, which is still a prototype. That is still a bit of a secret, so we will stop asking here. It is clear that Cor Pellikaan is still coming up with new inventions for international horticulture to create simple solutions that work.

This article was created in collaboration with UrbanFarmers and Qlipr. Text and pictures: Mario Bentvelsen. Video: BrokxMedia.

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Plant bugs like the European tarnished plant bug and the common nettle bug are a serious problem in crops such as aubergine, cucumber and chrysanthemum. Even in small numbers they can do considerable damage: abortion of the flower in aubergines, stem and fruit damage in cucumbers and splits in chrysanthemums. As soon as growers spot bugs or bug damage, they feel they need to intervene fast with products that are harmful to the biological predators they are using for other infestations, marking the beginning of the end of their biological pest control.

Bugs usually enter the greenhouse from outside. They can arrive early in the season but most sightings of bugs, particularly the most harmful species, the European tarnished plant bug, are reported in the summer months. A good method of spotting and monitoring the presence of bugs can help growers decide when to use pest control products. It would be even better if bugs could be effectively eliminated from the plants with traps.

Pheromones and plant aromatics

A trap with a pheromone attractant for the European tarnished plant bug (Lygus rugulipennis) was originally only available for outdoor use, mainly in strawberry crops. Producers of biological pest control Entocare biocontrol C.V. and Wageningen University & Research have been working with a number of growers in the Netherlands to study and optimise the use of the trap and pheromone in the greenhouse. This trap is now available for detecting the presence of the European tarnished plant bug in various crops (aubergine, cucumber).
The traps were tested in a season-long trial and show peaks in the occurrence of bugs (Figure 1). The relationship between the numbers of bugs caught and the damage they cause is currently being investigated more closely. The level of the peaks and the increase or decrease in the numbers captured in weekly counts help the grower decide which crop protection measures to take.
Trapping bugs certainly helps control them but as yet it is unclear what proportion of the bugs already present can be eliminated with traps. The distribution of bugs across the greenhouse is very irregular: catches in traps show no evidence of bug hotspots.

Concentration critical

During the trial it was discovered that the luring effect of the pheromone works best in the presence of plant or crop aromatics. A simple pheromone trap catches fewer bugs than a trap with the smell of the crop in the background. But it is mainly the males that are attracted by the smell of the pheromone, so the researchers have set about finding attractive alternatives to lure females as well. Their main focus is on plant aromatics.
Several plant substances that seem to attract the females have already been identified. Lab trials indicate that the concentration at which the aromatic is offered is critical, however (Figures 2 and 3). Too little fails to attract them while too much scares them off. Some substances are attractive to both males and females (substance B) while others only attract males (substance D) or only females (substance A). The research is now focusing on finding the right substances, or combination of substances, and on finding a formulation that will go on producing the right intensity of aromatics over a long period of time in practice.

Trap colour and shape

The funnel trap with pheromone which researchers are currently using needs to be further optimised for catching bugs. Video recordings of males landing on these traps showed that less than five per cent of landings on the trap actually resulted in capture. The colour and the shape of the trap will be studied in more depth in future research, along with ways of further optimising the trap. If a combination of pheromone, plant aromatics and better traps proves successful in trapping both males and females, this will open up new opportunities for tackling the bug problem.

Biological control

Besides observations, the aim is also to improve biological control with an effective combination of attractants and biological agents. To begin with, the researchers are looking at a biological agent based on an insecticidal (entomopathogenic) fungus. They are investigating whether it is possible to use attractants to target fungal spores better in the crop in order to increase their effectiveness in controlling bugs. With a modified formulation of the fungal spores and an effective method of transferring them to the bugs, it has been shown that it is possible to get at least three to four times more spores onto a bug.
The next question is whether this combination of methods (luring, infecting and transferring) actually helps combat the infestation. Further research on this will be taking place during the coming year.

Summary

For some years now, scientists and growers have been working together to come up with a better monitoring and control plan for the European tarnished plant bug. A pheromone trap that captures males has already been successfully tested. Research into attractants for females has yielded some new substances that are effective, offering new options for controlling this bug.

Text and image: Rob van Tol (Wageningen UR), Maedeli Hennekam and Daowei Yang (Entocare biocontrol).

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Evaporation - and therefore energy loss - can be limited by removing excess foliage. This principle is, however, applied to only a few crop varieties. Professor Marcelis sees oppurtunities for sweet peppers, tomatoes, aubergines and roses.

‘Sweet peppers do not need their lower leaves for production, for example. These leaves do not contribute to photosynthesis, while they continue to evaporate moisture. Without this evaporation you could save energy. This is why you should remove the lower foliage in late summer or early autumn. Dutch growers, however, believe that this will take too much work. Their answer to the research proposal we submitted was "We’re not going to do that", because they did not expect it to yield any substantial profits. In cases like these there is no point in conducting a study to assess the production increase resulting from de-leafing, or whether or not de-leafing has a beneficial effect on susceptibility to disease due to the improved air circulation around the plant. Aubergines are another crop that would benefit from de-leafing in late summer or early autumn.

‘De-leafing sweet peppers is relatively easy: you simply tear the leaves off. You can easily estimate the results achieved in a calculation model. However, due to the immediate rejection by the horticulture industry this study was never given a chance to prove the benefits of de-leafing.

‘Tomato growers, on the other hand, have embraced de-leafing as a useful practice. Research is now being conducted into the amount of foliage that is genuinely needed by a plant. Plants produce too much foliage in winter, in any case. We are conducting in-depth research into this.

‘When growing tomatoes, you remove the leaf at the head of the plant before it has fully formed. The plant will then no longer need to spend any energy on the development of that leaf. This is already being done in practice, but the process could be improved. Research is currently being conducted on this by Wageningen UR Greenhouse Horticulture in Bleiswijk, but I am not directly involved in this project.

‘We have not yet reached any definite conclusions with regard to how much foliage is desirable. I am convinced that de-leafing would also be useful in the cultivation of roses. Roses waste a lot of energy on unnecessary foliage. If all the sugars now seeping into bent branches would be made available for production, you could probably harvest many more branches. We have to come up with a smart solution for that. I am certain that far too much energy is being lost.’

The emergence of LEDs, climate control and a growing insight into plant physiology allow crops to be grown in greenhouses all over the world. Does greenhouse horticulture in the Netherlands have a future?

‘There are actually many advantages to greenhouse horticulture in the Netherlands. Summers aren’t so hot. There could be more light in winter, but there are other greenhouse horticulture areas - such as in the United States - where winters are much colder. Many regions have to cope with regularly extreme weather conditions. No, greenhouse horticulture certainly has enough advantages.

‘It is, however, a fact that horticultural developments are taking place at an accelerated pace all over the world. The Netherlands is a front-runner with respect to efficiency. If you wish to retain that leading edge you will, however, have to continually come up with smarter solutions with regard to efficient cultivation, marketing, quality and vitamin and nutrient content. Innovation is essential to horticulture.’

Leo F.M. Marcelis (Elst Gld, 1963) studied horticulture at Wageningen University, where he obtained his PhD in 1994. He was a professor by special appointment of Crop Production in Low-Energy Greenhouses at Wageningen University until 2013 and team leader at Wageningen UR Greenhouse Horticulture. On 1 December 2013 Prof. Dr Leo Marcelis was appointed Professor of Horticulture and Product Physiology at Wageningen University.

Download the complete interview with prof. dr. ir. Leo Marcelis about diffuse glass, LED-lighting, urban farming, de-leafing and the effects on plants, energy consumption and cultivation strategy (login required).

Source/photo: Tuinbouwteksten.nl/Theo Brakeboer.