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Symposium on nature-inclusive horticulture:

Growers no longer afraid of bugs, now just finding the best balance

Greenhouse horticulture is on a journey towards resilient cultivation with more biodiversity. The time that journey takes is different for each grower. The challenge is to link as many possible paths as one can to lay a broad foundation.

This is how Helma Verberkt of Artemis summed things up Thursday afternoon during a Greenport West-Holland symposium on nature-inclusive cultivation. Appropriate, with the summer holidays approaching.

What stood out was that the chairman of the day came up with the summary at the very beginning of the afternoon after barely a few minutes. At that time, three speakers, a series of videos with practical stories from growers, a panel discussion with growers, and a series of workshops had yet to begin.

Chairman of the day Helma Verberkt of Artemis with the panel including Theo van der Knaap, Wilco Hofman, Ellen Klein, and Harry Wubben.

Comic images
Anyone who would have left after the conclusion of the chairman of the day would have missed a lot. No ready-made answers, but rather lines of thought, as well as research results and success stories that can serve as a foundation for the steps horticulture still has to take.

"What should we watch for in the next five years?" was a question from the audience to the panel at the end of the plenary session. "I think we are the ones being watched," grower Wilco Hofman of LS Santini replied ad rem. More and more growers are aware of this.

They have therefore started taking steps, some for decades and others only more recently. The examples passed by in four videos. Certainly not marketing pitches, but real stories from the greenhouse.

Among the flies flying around in the case of seed grower Cor van den Berg of Bergbloemen. The video produced comical images that made the room, filled with some 80 attendees, laugh. The video can be viewed at the bottom of this text.

Although the flies were a nuisance when making the video, it did show well what growers are doing about growing more resilient, natural crops. Cor, who runs a seed crop for Rijk Zwaan, lets the flies fly around to make pollinators nervous. That way, they start flying more, and there is more pollination, especially in crops where pollinators are otherwise less likely to do their work.

Eveline Stilma.

Videos featuring growers passed between the presentations in the plenary session. Eveline Stilma of Greenport West-Holland discussed how what seems possible in theory must also fit with practice.

She did so with a visual example of a fashion show for fashion brand Dior. Those creations are lovely, but can the models walk with them on or sit comfortably in a chair? No, was her conclusion. In the same way, what is researched in the field of biodiversity in greenhouse horticulture should also be applicable to the grower in and around his greenhouse.

Pieter Stolk of Stolk Brothers now sees this at his location, where they grow anthuriums. The use of pesticides was drastically reduced 30 years ago after his father suffered health problems and was replaced by biological control agents and later biostimulants.

Today, his crop is more resilient. Growers used to get nervous at finding five thrips on a sticky trap, Pieter acknowledged. Nowadays, twenty doesn't even scare them. The system solves it.

Roeland Berendsen.

Roeland Berendsen of Utrecht University took the audience through research on the microbiome the university is working on. The microbiome acts as an extra layer of the plant's defense system. With automation and phenotyping, researchers are trying to gain a better understanding of how the plant works in this respect so that growers can benefit from it in practice.

Harry Wubben of Funny Santini and Ellen Klein of Koppert also addressed the microbiome and the process in the soil. Together with the people around him, he is trying to make the plant less attractive to pests. The plant already knows how to do that, Ellen pointed out. The trick is to put it in the right position.

Mauro Gallo.

Mauro Gallo of Inholland was allowed to talk about biomimicry, in which bits of nature are applied in smart technological innovations (such as flapping drones). Gerben Messelink of WUR, on the other hand, looks outside the greenhouse again, where pilot projects are running with flower and herb strips next to the greenhouse.

In the Oostland, this already yielded insights on thrips at four growers, among others. Only six percent of the thrips found were the Californian thrips feared by growers. In the trial, it was found a lot precisely at the beginning of the summer, which leads the entomologist to suspect that the thrips fly from the greenhouse out into the roadside rather than the other way around.

In Bommelerwaard, where the province sometimes requires growers to shield their greenhouses from the outside world by planting trees around them, the researchers looked at which trees are best to plant from a biodiversity point of view. Probably not the Gelderland rose, which is popular with greenhouse whiteflies, but perhaps the willow because, of the trees studied, it had by far the greatest diversity of potentially useful insects.

Gerben Messelink.

Also useful: aphids can already be found in the trees early in spring. Growers would rather not have aphids, but biological control agents like to eat aphids and can thus gain strength in spring before they do any useful work in the greenhouse. Provided, of course, that the greenhouse is not hermetically sealed from the outside world, as sometimes seems to be the trend nowadays. Instead, biodiversity researchers are looking for the optimal connection between the inside and outside.

After a short coffee break, it was time for workshops. One about training advisers in nature-inclusive cultivation and the role of education in this, one about the earnings model, it also remains greenhouse horticulture with small margins despite all good nature intentions and one about resilient cultivation in practice.

Jantineke Hofland with the Disk of Resilience.

In the latter workshop, Jantineke Hofland-Zijlstra of consultancy firm Weerbare Plant and Frank Hoeberichts of Eurofins decided not only to broadcast but also to engage in a discussion with the audience. Jantineke presented the Disk of Resilience and also invited everyone to look at pre-biotics instead of probiotics. Bringing in something from outside can help, but the question is whether it always has the right effect.

Frank Hoeberichts gives an example of the microbiome. The more colored bars, the more diverse. Below the bar for potting soil, above for rockwool in tomato.

The workshop also raised that question among growers in the room. Some, for instance, have already gained experience with Trichoderma fungi but wondered in the session whether those fungi actually manage to survive in the rest of the system if (too) few further adjustments have been made here.

In short, should growers move step by step towards nature-inclusive cultivation, with more biodiversity and a more resilient crop, so that they keep track of what is happening, or move forward all at once?

There was no single answer to this in the workshop. However, the specialists, even outside the workshop, as well as the growers present, are aware of the importance of systems thinking. In it, they can immediately also wrap their heads around how peat-free cultivation, rightly noted by one grower as an additional complicating factor, can be overcome with the help of the possibilities that nature offers growers.

Video with flies in the greenhouse of seed grower Cor.

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