gerbera
Time for resistance
It’s always an exciting time when the first flowers appear in the new crop. We proudly put them in a vase at home so that we can continue to enjoy them after work. But after three years, you can’t drum up the same amount of enthusiasm for every variety. Sometimes I look forward to the next change of crop and sometimes I’m even quite pleased if a variety goes out the door never to return.
That came to mind last week as I was doing the rounds of the Dutch plant breeders. Lots of new species are introduced every year but only a few ever turn out to be real winners. It does seem as if breeders keep on producing more and more of the same thing, and the new ones often don’t even seem to be much of an improvement on the previous versions. Later on you discover that the flowers are very prone to mildew, they aren’t particularly productive, or they are too susceptible to pests and diseases, causing high losses. Every species has a nice little sign describing their performance but they say nothing about how sensitive the plants are. Surely there’s a better way?
If breeders could provide a little more information up front, it would make it much easier to choose the right plants. I also think that highlighting this information would shift the focus more towards breeding resistant crops, which is something that’s urgently needed. If it’s possible to produce a burger from a 3D printer, surely it’s possible to produce a young plant that’s resistant to pests and diseases?
This has particular potential in the current market, in which there is a lot of demand for clean, sustainably produced products. Some vegetable crops already come with information about how sensitive the variety is to diseases like mildew, for example. So the first step has already been taken, and it would be a nice challenge for gerbera breeders to follow this example. Who will be the first? I’m looking forward to visiting the show greenhouses of breeders like Dümmen Orange, Florist and Schreurs this year and seeing neat little signs stating what form of resistance all these wonderful blooming gerberas have.
Marius Mans
Gerbera grower in the Netherlands
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Controlling Echinothrips americanus with predatory mites and bugs
As every grower knows, thrips are a huge problem in ornamentals grown under glass. The usual suspect is the Californian thrips, a species with a strong preference for flowers. But in recent years another polyphagous thrips has been increasingly raising its head: Echinothrips americanus. Without timely intervention, this typical leaf-dwelling thrips can cause considerable damage to ornamentals such as gerbera and rose. Scientists have been taking another close look at how to control this thrips with a range of species of predatory mites and bugs.
In this study, striking differences were found between the four species of predatory mite used and the controlling effect was boosted in some cases by providing pollen. Predatory bugs in the Miridae family have been found to be very effective predators of Echinothrips but the options for using them very much depend on the type of crop.
Switching methods
Unlike the Californian thrips, which is a typical flower thrips, Echinothrips americanus prefers leaves. It is easily identified by its black body with two distinct white spots on the wings. But because it often hides away low down in the crop, its presence in the greenhouse can be something of a surprise. Although the species has been present in the Dutch greenhouse horticulture sector for about 20 years (it was imported from North America, as its name suggests), we still know very little about this creature.
In recent years there has been a clear increase in this species at nurseries switching to integrated pest control. The reduction in the use of broad-spectrum insecticides has given this thrips more chance to establish itself in crops. To avoid disturbing biological control of other pests, it makes sense to also tackle this insect with natural predators. Predatory mites and bugs are good candidates for this.
Control with predatory mites
In the lab, the researchers investigated how susceptible the various stages are to predatory mites and how many individuals of each stage are eaten per day. This was tested with the predatory mites Amblyseius swirskii, Amblydromalus limonicus, Euseius ovalis and Euseius gallicus. The latter two Euseius species establish readily in rose and are therefore interesting candidates for this crop.
Striking differences were found between the species. A. limonicus ate the most Echinothrips larvae, followed by E. ovalis and A. swirskii (see figure). A. limonicus also laid the largest number of eggs out of these mites. Surprisingly, the thrips were more or less left untouched by E. gallicus. The exact reason for this is unclear.
Interestingly, the pupae were also susceptible to the mites. This immobile stage, which is also found on the leaf, cannot defend itself and is therefore suitable prey.
With the exception of E. gallicus, all species of predatory mite ate the pupal stage. However, as the pupae are much larger than the larvae, the number of individuals eaten per day was a lot lower than in the larval stage. None of the predatory mites ate adult Echinothrips. In addition to the number of thrips being eaten by each individual predator, an important indicator in pest control in a crop is how well a predatory mite establishes itself and in what densities: after all, a high density can easily make up for lower predation rates per individual.
Results in the crop
The predatory mites A. swirskii and A. limonicus were compared in a greenhouse gerbera crop, with the results matching those in the lab quite closely. The thrips were controlled better with A. limonicus than with A. swirskii. This difference has also been observed in other studies with roses and sweet peppers.
Curiously, though, Echinothrips often doesn’t disappear completely: it is somehow able to survive the pressure from the predatory mite. So in a subsequent study the scientists looked into whether control could be improved by offering pollen as an alternative food source. Pollen can massively boost the density of predatory mites, which could lead to better pest control. The downside is that the Californian thrips also feeds on pollen, potentially causing scenarios that are detrimental to thrips control.
Effects of pollen
An important question, therefore, is whether this also affects Echinothrips. With bulrush pollen, the answer was a resounding no. Unlike with the Californian thrips, there was no impact on development time, egg laying or population development whatsoever. This is helpful in that it means supplementary food can be provided for predatory mites selectively, as long as there are no Californian thrips present.
The effects of pollen on thrips control were tested on non-flowering pepper plants using the predatory mites A. swirskii, E. gallicus and E. ovalis. Providing pollen increased the densities of all these mites. Control of Echinothrips using this method was significantly better with A. swirskii but despite the higher densities there was no control effect with E. gallicus. E. ovalis responded extremely well to pollen but the control effect was just as good on plants without pollen.
Predatory bugs
It has been known for a long time that the bug Orius majusculus is an effective predator of Echinothrips on sweet peppers. Orius is used to control thrips in this crop with great success. But the bug doesn’t establish in many ornamental crops. In recent years, scientists have been looking at the effect of omnivorous predatory bugs in the Miridae family on gerbera. In addition to Macrolophus pygmaeus, various Dicyphus species such as D. maroccanus, D. tamaninii and D. errans have also been trialled. All these species controlled thrips extremely well. Plants were made completely clean and remained so.
The bugs seem to be excellent candidates for preventive use against a range of pests and they can maintain themselves well because they eat a variety of prey and plant sap. This can also be a disadvantage, however, because feeding on plants can cause flower damage. Further research will be carried out in the future to see whether and when that happens and whether it can be avoided. The use of these bugs in gerbera could be a breakthrough in biological control of Echinothrips as well as other pests. Future research in other crops, such as roses and pot plants, is planned to ascertain whether the use of predators with banker plants can be supported.
Summary
Echinothrips is appearing more and more frequently in ornamentals grown under glass. In trials with a number of species of predatory mite, A. limonicus provided the best control while E. gallicus had little if any effect. Control with A. swirskii was improved by offering pollen. Besides predatory mites, predatory bugs of the Miridae family were found to be excellent predators but further research is needed to prevent potential flower damage and to improve establishment in different crops.
Text and image: Gerben Messelink, Somayyeh Gasemzadeh and Ada Leman (Wageningen University & Research).
Diffuse screen results in more generative gerbera crop
Gerbera grower Batist, of Maasdijk, the Netherlands, fitted a new, moveable climate screen with improved light diffusing properties into one of its greenhouses this spring. Due to less direct radiation, the crop is less quickly exposed to stress and ultimately on sunny days more light can be allowed to enter the greenhouse. The combination of better light distribution and less shadow results in a more generative crop that yields more.
Thanks to the new screen installed by Ruud Batist this spring, he no longer needs to whitewash the greenhouse. He was quite pleased with the diffuse coating that he applied each spring but the permanent layer of chalk also blocked out light and heat when it was not necessary. In addition the radiation entering through open windows was sometimes too high in places, causing sensitive varieties to visibly suffer.
Perform better
“I knew it could be better,” says the mini gerbera grower. “Therefore last year at another location we installed a Harmony screen with a shading percentage of 35 per cent, which also has light diffusing properties. This meant I could be more responsive to the circumstances. This spring we installed a variant on the further developed New Harmony line in an entire greenhouse. I am convinced that this will perform even better.”
More generative
Although Batist can’t make an objective comparison between the new screen, the classical type and the diffuse coating that he previously used, he says he is very satisfied with its performance. “The new fabric lets more light through and we have a more generative crop. Several colleagues within our growers’ organisation, Colours of Nature, work with the classic screens and we regularly meet in the greenhouse. They agree with us."
The difference in generative growth is so large that the gerbera grower is at odds with the usual day length regimes. “Normally, under cooler, fertile growing conditions, such as those we experienced up to mid July, you need to maintain shorter days to keep the crop in a sufficiently generative state,” he says. “However, this screen lets through so much light without passing the critical value of 1,000 μmol, that the plants receive a generative boost.”
Batist can reduce the hours of darkness and the resulting higher light sum is, as a rule, converted into extra growth. “Many of my colleagues start to darken the greenhouse around 1 July but we can maintain a longer day. It can only translate into higher productivity.”
Further developed
Paul Arkesteijn, of Svensson, nods affirmingly. “The first generation of Harmony screens was introduced eight years ago and developments have been ongoing," he says. “At the time it was the first moveable climate screen with diffuse properties. The big difference with previous fabrics was that the usual aluminium strips in the open, knitted cloth were replaced with white plastic strips."
According to Arkesteijn these screens allow more light through which is subsequently distributed wider. By varying the number of white strips in the cloth, gerbera growers can chose a screen that shades out 25, 35 or 45% of the light.
“Three years ago we picked up the thread again,” says Arkesteijn. “In the meantime, a lot of new, independent research had been carried out into the effects of diffuse light in crops. Based on that we wanted to research which aspects of our screens could be further improved. Growers are always raising the bar higher, both for themselves and for their suppliers. Our R&D department tested several new materials and the result of that exercise is the new series.”
According to the screen specialist the diffuse property of the fabric has above all improved in the screens with a lower shading level. “That makes these versions very interesting for gerbera and rose growers for example,” he adds. “The 25 and 35 per cent versions of Classic Harmony are already used a lot in these crops. We know that when the radiation is more than 1,000 μmol PAR a gerbera crop can experience stress. Measurements show that in Batist’s greenhouse, the light level remains well below this figure under the new screen. It has a shading percentage of 23 per cent.”
Less stress, more light
Better diffusion offers several advantages. Firstly you can allow more light to enter the greenhouse before the crop suffers stress from the high direct radiation. Secondly, better light distribution reduces the amount of shadow from greenhouse parts such as gutters, columns, air mechanisms and (trellis) rafters.
Arkesteijn: “The results of a trial under practical circumstances show that under the new climate screen, the crop in the shadow receives 32 per cent more light than under the first generation screens. The sunlight is more evenly spread over all plants and all parts of the plant. The result is a more uniform and faster growing crop.”
Another step further
Batist notes that the new climate screen offers him even more opportunities to optimise the growth factor, light. “The plant balance and bud formation are influenced by many factors,” he says. “You have to use screens during the lighter months to protect the crop from excessive radiation. Whitewash offers protection but also prevents light entering when it’s not necessary. In this respect the classic screen was a clear improvement. This new screen goes a step further and enables even more light to be converted into growth and production.”
Cautious
The grower says that he hasn’t been using the diffuse climate screen for long enough to confirm his high expectations with hard figures but he expects to have them within a few months. “When comparing nurseries or different locations with varying systems and varieties even within one company you need to be careful,” he says “However, I’d be surprised if over the long term this greenhouse doesn’t stick out above the rest.”
Paul Arkesteijn also believes this new screen will be an asset to gerbera growers, among others, even though it wasn’t tested on gerberas during the development phase. “We can’t attach any crop related figures. However, we know the transmission properties inside-out and they are excellent. They are the result of three years intensive research."
Summary
A new type of climate screen with improved diffuse properties makes it possible to admit higher light levels during gerbera cultivation. This produces a generative crop response. The reduced shadow from light intercepting greenhouse parts and equipment also results in more uniform growth. On balance, this should lead to higher production.
Text and images: Jan van Staalduinen
Much to gain with improved control over lighting installations
Assimilation lighting has a big impact on the greenhouse climate and - when the electricity is generated on site - on the efficiency of the energy generator. Optimising the control of the lighting installation leads to a gain in both areas. Two growers and their suppliers explain how they achieved it.
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Less energy input yields as many or more gerberas
Since 2014 Dutch gerbera grower Reijm Nieuwerkerk has been using a system to actively ventilate the greenhouse air as part of its Next Generation Growing strategy. The continuous refreshment of the air provides an optimal microclimate at the bottom of the crop. The company is producing the same quality gerberas with less energy input.
Reijm Nieuwerkerk cultivates 5 ha of pot plants and 3.5 ha of gerberas at three locations in Nieuwerkerk aan den Ijssel, near Rotterdam, the Netherlands. Annually the company produces 4.5 million pot plants and 16 million gerberas in many colours, from large flowering to minis.
Cultivation is in stone wool substrate in a gutter system. A double screen, comprising a black out and energy cloth, has been installed at the top of the greenhouse. A CHP cogenerator with a flue gas cleaner for CO2 production also generates electricity for the lighting (95 µmol).
Active ventilation
Last year, for the Next Generation Growing, the Active Ventilation System (AVS) by Van Dijk Heating was installed in 7,500 m2 of gerberas. This year the area has been extended by 17,500 m2. The system comprises a wall unit made of plastic which contains a fan, mixing valve, heating element and a filter. From the unit and running along the greenhouse wall is a PVC pipeline which acts as the distribution system. Air hoses that contain small holes for air injection are connected to the pipeline. The air hoses hang under the rows of plants.
The greenhouse is dehumidified thanks to active ventilation of the greenhouse air that is mixed with relatively dry outdoor air. The heating element provides low value heat (40ºC water from CHP) for warming the external air to greenhouse temperature.
Learn from practise
The reason for installing this ventilation system is to produce the same or more gerberas with less energy. “The art is to input the right amount of energy at the right moment. In the past we used to turn on the minimum pipe for this but actually we didn’t know exactly what we were doing,” says Jaré Reijm. He runs the family business together with his brother John. Over the years the grower has carried out several trials with gerberas and therefore has learned a lot about the greenhouse climate without having made too much investment in his nursery. “But then it’s not easy to further improve the greenhouse climate, although also not easy to make an investment and then to earn it back. However, installing this system has worked well. Last year we achieved a good cultivation climate. We were able to keep the climate under the plants somewhat drier and above the plants more uniform,” says the grower.
Better temperature distribution
Joek van der Zeeuw, of Van Dijk Heating, explains: “With traditional methods of growing you always need some gaps in the screen and you have a cold dump were you don’t want it. Now, by using this system to inject outside air into the greenhouse you obtain a small amount of over pressure. That is enough to ensure that no cold air enters through a hole or gap so the temperature distribution in the entire greenhouse is more uniform.”
The grower indicates that the temperature difference used to be 3ºC and now is just 1ºC. Further, he would like to better control the microclimate between the plants. The holes in the hoses where the air comes out are therefore set to point upwards. The air that is injected into the greenhouse has been mixed with air from outside and so contains less moisture. Due to a lower RH the crop is less susceptible to disease. “By continuously refreshing the air, we now have a good climate at the bottom of the crop. As a result we think that the flowers are less susceptible to fungal diseases such as Botrytis. And we can achieve this without using the minimum pipe,” says Reijm.
Drive controlled fans
The system has an air-displacement capacity of 6 m3 per m2. The fans in the wall units are equipped with energy-efficient EC motors that are controlled by a computer network. The fans can be reduced to 50% of the capacity, so they only consume 100 Watts of electrical energy for dehumidification. At full output 800 Watts is needed. Reijm tries to run it for as long as possible at low power, until the valve for the outside air is fully open. If then the humidity in the greenhouse rises, the speed of the fan is increased gradually. In this way the grower makes the most efficient use of the system.
Normally, the ventilation units are fitted in an outside wall to be able to draw in outside air. This was not possible in a partitioning wall with the pot plant greenhouse. Here separate units were made that draw in outside air from the top and have air passage through the roof. This suction hole in the roof is covered with a flat sheet so that the roof cleaner can drive over it.
Winter and summer
“Due to the active ventilation it is possible to use the energy screen more in the winter months because we can better control the climate, the humidity and the temperature distribution,” says the grower. Last summer he used the system for the first time for cooling. This worked well. Cooling was achieved by sucking in outside air and injecting it into the greenhouse.
Reijm: “Despite the tropical temperatures outside the greenhouse remained cool for longer. Even when it was 30ºC outside, it remained 25ºC under the crop. Because we measure everywhere under the crop, we see a difference with the traditionally grown crop. Because the temperature is lower for longer, we can open the vents later. This keeps the CO2 inside. Due to the cooling, the crop remains more active so that the quality of the flowers is better. The diameter and stem length remained the same during the summer. However, this was not the case with the traditional cultivation. The flower was smaller and the stem was shorter.”
Pure CO2
Reijm uses the system for dehumidifying and cooling, but not for heating. The grower doesn’t dare to use the latter for Next Generation Growing. “By heating from underneath we would push the crop too much. As a result the crop would transpire more, which would result in a higher humidify. Then we would have to get rid of the moisture in one way or another and that costs energy.”
A disadvantage of the system is that because less heat is required, the grower has a CO2 shortage. Because the CHP cogenerator produces heat, which the grower would have difficulty getting rid of, it only runs to produce electricity for the lights. However, in the summer months it doesn’t run for long enough to provide sufficient CO2. This summer the grower will have to buy and inject pure CO2.
Uniform growing conditions
The grower would like to have the same growing conditions for all the gerberas. Because they change the crop every three years, they will be able to install this system in the last hectare of gerberas next year. Installing it while a crop is present is not wise, according to Reijm. In addition, they will replace the entire cultivation system so they can do everything at the same time.
Summary
Since 2014 Dutch nursery Reijm Nieuwerkerk has been implementing the Next Generation Growing, a system that includes active ventilation. The grower can dehumidify the greenhouse air by mixing it with air from outside. He can produce the same number of gerberas with lower energy consumption. The continual refreshment of the air provides an optimal microclimate at the bottom of the crop. As a result flowers are less prone to fungal diseases such as Botrytis.
Text/photos: Harry Stijger
Pioneering with the Next Generation Growing
Marius Mans of Mans Flowers is one of the first growers in the Dutch ornamental plant cultivation sector to firmly adhere to the guidelines of the Next Generation Growing. "You become more conscious of your energy usage and that leads to savings. But optimizing growth remains the primary objective."
Modern growers are increasingly becoming entrepreneurs who must know all about the many aspects of a modern greenhouse cultivation company. "Nowadays, regulation and control by a climate computer play an essential role in any of the larger companies", says Mans. However, despite that fact, he believes that having green fingers is still very important. "Certainly in the case of the Next Generation Growing, it is about making the right observations and using this information to choose the correct settings at the right time."
"Insight into every detail of the plant's growing process leads to many other opportunities."
In the last few years, Mans Flowers has developed the Next Generation Growing even further. He became more aware of his energy consumption, which was the first step towards making savings. However, the biggest added value is the optimal growth that he has experienced. "An optimal greenhouse climate greatly improves quality. I can now also deliver top quality products during the more difficult growing periods in the year. Insight into every detail of the plant's growing process leads to many other opportunities."
Balanced greenhouse climate
Mans has recently switched to Priva for his climate control needs. "I have made that choice because it gives me more options to achieve the ideal, balanced greenhouse climate. I get calculations in advance based upon a variety of parameters. And that helps me to take the right decision at the right time in order to achieve my goal."
"A lot of knowledge has been gained about biological control in the Netherlands, which has given us an advantage over growers from other parts of the world."
Fighting diseases and pests also has a very high priority, says Mans. "The gerbera is a bushy plant with a lot of leaves close to each other, which makes it difficult to treat diseases and fight pests. For that reason and also because we want to demonstrate corporate social responsibility, biological control is extremely important. It has to do with having the right balance and an integrated approach. A lot of knowledge has been gained about biological control in the Netherlands, which has given us an advantage over growers from other parts of the world. That helps us to be able to hold and improve our strong position in the future."
Source/photo: Priva.