Researchers and companies are continually developing new techniques for greenhouse production. Therefore, in principle crop protection can reach a much higher level. But to achieve this, all these techniques need to be integrated. A system has been developed within the Gezonde Kas (Healthy Greenhouse) program that links them all together.

Gezonde Kas is a large Dutch-German project comprising 10 research institutes and 22 commercial companies. It was completed in the middle of 2015 and achieved its goal: The development of an innovative integrated crop protection system. The different parts of the system alert the grower to the presence of pests and diseases, even before any symptoms are visible. The system then helps the grower to make decisions. Furthermore, the system suggests measures that are based on the use of as few chemicals as possible.
Many of the techniques were known already but during the project were adapted for use in practise, geared to fit one another and integrated into one system. This has, to a large extent, been set up in a trial greenhouse in the research centre, Versuchszentrum Gartenbau, Straelen, Germany.

Ready for translation

Project leader Carolien Zijlstra, of Plant Research International (part of Wageningen UR, the Netherlands), is a molecular biologist by origin. “At PRI we have the capability to identify crop predators based on DNA or proteins. We need just one fungal spore to detect the problem at an early stage. But the method needs to be converted for use in practise. That was one of the reasons for starting this project. And, in fact, many more methods are ready for translation,” she explains.
The Interreg IV-A project is financed by the EU (EFRO), the Dutch and German Governments as well as businesses. The new system consists of four process steps. For each of these, suitable methods have been developed for use in practise. “They have been developed for large innovative nurseries but parts of them can be used by every grower,” she says. “Growers can purchase all these products or choose from the possibilities.”


Step one is called Gezonde (Healthy) Start. “Just before the start of the crop you check the surroundings and materials to make sure they are free of pests and diseases and take preventative measures to avoid contamination,” says Zijlstra. The Luminex-test shows exactly if seed, plant material, water or substrate contain pathogens. “The system works with very tiny balls that are coated with antibodies or DNA. If a pathogen is present the coating binds with its protein or DNA. If that happens the tiny balls light up under a laser beam and you know which pathogen is present. You can test for a hundred pathogens at the same time.”
It’s impractical to test all the plants in the greenhouse, so pre-screening with another technique is useful to highlight the potentially infested specimens. This is made possible with a chlorophyll-fluorescence camera (see below).
This first step also contains two disease-suppressing measures: Firstly a top layer on the substrate ensures that predatory mites become better established and therefore can better attack thrips. Secondly, disease-suppressing substrate reduces the risk of contamination by Sciaridae by 80%.

Spore collector

The second step consists of advanced monitoring. This can be on a macro-scale; the whole greenhouse, or a micro scale; plant- or leaf level. Several techniques are available for both levels. The chlorophyll-fluorescence camera (CF-camera), for example, passes over all plants and assesses whether photosynthesis is being carried out properly. If not, it can be an indication that plants are contaminated. The multi-spectral image sensor is another method for detecting suspicious spots in the crop but uses a different technique. It sees better than the human eye.
Other techniques that detect on a macro level are the electronic nose and the spore collector. The latter collects air-borne fungal spores which are later analysed. “If you discover contaminated areas with the macro screening you can analyse them further using the micro scale techniques,” says the project leader. For example, the previously mentioned Luminex-test is very suitable, but there are other methods that can detect diseases present in the plant, such as TaqMan- or a LAMP-test. The Nsure plant vigour test indicates whether specific genes in the plant are turned ‘on’ or ‘off’. This indicates if the plant is diseased or not.
In the meantime the wireless sensor network keeps a check on climatic differences, in case something needs to be altered here.


“With this combination of steps you highlight diseases which you can’t yet see with the naked eye. The CF-camera notices if the plant is in trouble while, visually, nothing appears to be wrong. Then by implementing the other tests you can figure out what it going on. Also the vase life of flowers can be predicted with such a camera,” she says, describing the advantages of the new technology.
The disadvantages are the costs: the CF-camera currently costs around Euro 100,000, and it’s the same for the electronic nose.
After the problem is detected a decision has to be made. The third step in the process involves interpretation of the data and giving advice. Various decision support systems are available for this. The Climate Vitalizer gives advice on achieving a more homogenous greenhouse climate. Notify Me predicts crop development and a further three systems can analyse the risks of Botrytis and pest insects as well as propose control measures.

Precision spraying

These measures fall within process step four and relate to better climate control and pest management. The preferred method is a non-chemical approach. The project has developed a new strategy using endophytes, which improve the effectiveness of biological pest control. “Various natural predators eat both the pest as well as the plant. If you supply the plant with an endophyte – a useful microorganism that lives in the plant – the plant becomes less attractive to the natural predators and so these focus more on the harmful organisms,” says Zijlstra.
One of the most important parts of the project is the development of precision spraying. Cameras on the spray robot “see” the chlorophyll and only spray the plant and not the ground or into space. This saves 50% of the crop protection product. The next step is to combine it with the CF-camera. This detects firstly the suspicious areas so the robot only needs to spray these areas. This can save up to 70% of the product use.
The project Gezonde Kas has come to an end but a follow-up project for pot and container cultivation (tree nurseries) is in the pipeline. Researcher Zijlstra hopes that growers and horticultural advisors will quickly pick up on the techniques that have now been adapted for use in practise.


The project Gezonde Kas (Healthy Greenhouse) has developed an innovative four-step system in the field of crop protection. Key words are prevention, early detection, better control of climate and disease development and a reduction of chemicals. In all cases innovative techniques have been made adapted for use in practise and are described in this article.

Text: Tijs Kierkels. Photos: Wilma Slegers