Grodan’s third seminar for international propagators:

Plant health and sustainability in propagation key priority for Grodan

Grodan’s third seminar for foreign propagators attracted a lot of interest. Around sixty people came to hear all about the latest developments in the fields of plant health, propagation methods and sustainability in the propagation of vegetable plants.

The first speaker, Thorben Looije of the research company Valto, explained how cross-protection can help in controlling the damage caused by the tomato disease Pepino mosaic virus, or Pepmv for short.

This virus, which is a member of the genus Potexvirus, is very contagious in the event of contact with plant-juices via the hands, clothing and possibly also bees and seed. Once it has entered a plant, the virus will spread throughout the entire plant within a few weeks and the plant’s leaves and fruit will start to show symptoms. There are currently four Pepino strains (PE, EU, CH2 and US1) that cause damage.



The theory behind Valto’s cross-protection method is based on infecting plants with a related, but milder variant of the virus to prevent the risk of the plant being infected by its morel virulent relative. The mild variant will make the plant a bit sick, but the right climate conditions will help it recover. Valto has meanwhile developed solutions in the form of cross-protection with a mild variant for three of the four virulent strains. The only strain for which it hasn’t yet found a solution is US1.

The intention is to infect plants at the earliest stage possible during their propagation, to prevent the risk of the more harmful strain affecting them. This deliberate infection of the plants can be done by hand or by spraying them with carborundum powder. All the large propagation companies in the Netherlands are currently using this cross-protection method (in 1100 of the 1500 to 1600 ha).

Thorben Looije emphasised that hygiene remains important in minimising the risk of this disease: each order must be handled separately and people working with Pepmv must disinfect their hands and change into clean clothing and footwear whenever necessary.
Valto is continuing its research to find a mild strain to control US1 and is investigating new options such as the possibility of controlling Agrobacterium with antagonists.

Grafting, pinching and de-leafing plants

How do you obtain the plants your customers want? Cornelis Ammerlaan, an independent adviser and specialist in the field of grafting, explained to the propagators how they can meet their customers’ requirements through a combination of grafting, pinching and de-leafing plants. According to the adviser, customers want healthy, vigorous plants with good roots and generative growth. The resources that propagators need to achieve this are ‘grafting’ and preferably modern greenhouses with facilities such as insect screens in the ventilators, hard floors with intermittent irrigation, assimilation lighting and CO2.



Pinching will cause the plants to branch. It can be done in two ways: just above the cotyledons or above two (real) leaves.The latter method is used most commonly. The plants will then be vigorous enough to vegetatively develop shoots and form clusters from the fifth and sixth leaves.

Ammerlaan explained that there are more ways of promoting uniform growth: spacing the plants further apart at the right time, when the leaves begin to touch one another, and removing the second leaf when pinching the plants. According to the adviser, when you remove the second leaf at pinching you take away excess energy, promoting more uniform growth of shoots and branches and better development of the clusters. When conditions for the plants are not optimal, i.e. low light levels, an alternative is to remove 50% of the second leaf. The shoots will then still have a little energy left to develop. Ammerlaan is also in favour of lighting: 6.000 lux is good, 8.000 to 10.000 lux is even better.

Vital water

Osteopath Remy Mosch and Ineke Moerman of Vitally grown explained how the use of vital water can contribute towards the quality of plants. When Moerman, as one of Mosch’s patients, found her problems of fatigue and headaches cured by drinking vital water and also observed positive consequences among farm animals, she and Mosch started to investigate possibilities in horticulture. The fine distribution of minerals and trace elements in vital water makes it easier for plants to take them up.

Research was carried out at various horticultural facilities, one of which was plant nursery Beekenkamp. In a trial carried out between 2010 and 2013 plots irrigated with vital water were compared with others that were irrigated with ordinary water. The plants that had been irrigated with vital water proved to have a better branched root system and showed uniform development. Vital water was also found to lead to positive results at the 52-ha tomato farm Royal Pride in Wieringermeer. Frank van Kleef now even exploits his use of vital water as a marketing tool in his 'Vitalientjes' (‘Vitalins’).

You need a VT-Vitalizer to produce vital water at your nursery. It has to be installed behind the irrigation unit, where it will restore the water’s original vibration.


Precision Growing in propagation

'Passionate about Precision Growing' is Grodan’s philosophy. And according to Hans van Herk, propagation specialist at Grodan, that’s no empty slogan. Precision Growing can have a lot of advantages in propagation, such as savings in water and fertilisers and compliance with statutory requirements. To realise those advantages you do have to use stone wool blocks with good capillary action, i.e. Plantop or Pro. They will enable you to control their water content efficiently. Good capillary action is all the more important with the latest developments: slabs that are10 cm high instead of the usual 7.5 cm, and the new Elite system involving only one plant per slab.

Precision Growing leads to savings in the consumption of water and fertilisers and enables propagators to work in a more sustainable way. Most impressive of all the benefits of Precision Growing, however, are the plants’ excellent generative growth and their healthy, vigorous root systems!


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