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Sauna treatment for strawberries grants a clean start

By applying a special temperature treatment using aerated steam to slightly tease strawberry plants and stems, it is possible to produce disease-free plant material without chemicals. This, in a nutshell, is the principle behind Plantsauna. Four years after the first Dutch users began employing the technique, Moleda, the company behind the product, is active in an increasing number of countries with a growing base of users.

"We now have 26 Plantsaunas in use worldwide," says Kars Vreeswijk. "In many distant countries such as New Zealand and South Africa, plant nurseries are using our technology to control strawberry mites. In Canada and the United States, where we have the most users, growers are using our technique to combat strawberry mites, anthracnose, and Xanthomonas."

Additionally, Moleda has observed that users in Spain, Italy, Poland, and the Netherlands, use the Plantsauna treatment to ensure their plants are free of fungi and insects.

Plants ready for sauna treatment in South Africa

The fundamental principle of the sauna process was discovered by the University of Florida and NIBIO, a Norwegian research institute. Marten Barel and Ole Myhrene further developed the technique for practical application. Plantsauna is now available from Moleda. "First, we treat the plants with aerated steam at 37 degrees Celsius for one hour. After that, the plant rests and cools down for an hour, followed by a second heat treatment at 44 degrees Celsius. Depending on the fungus, pest, or bacteria being targeted, this final treatment lasts between 2 to 4 hours."

Plant sauna in use in Mexico

Remote Monitoring
In recent years, the system has seen minor developments. For instance, it can now be fully monitored online via an IoT system. "This is a standard add-on that comes with Plantsauna. By logging into the machine, users can immediately see the plant's temperatures, providing remote insight."

Once the Plantsauna is operating, the user can take a break, thanks in part to the online monitoring. "The timer for the treatment only starts once the required temperatures are reached."

To measure the temperature, sensors are manually attached at the top, middle, and bottom of the pallet of plants entering the Plantsauna. The sensors are connected to cables. "The only other manual task is driving the pallet in and out and transferring the plants from the usual wooden crates to perforated plastic crates for the sauna treatment."

Bert van Geffen and Cas Barel at a Plantsauna for Bert's Berry Farm in New-Zealand

Other Crops
Initially, the focus was on introducing the Plantsauna for propagating strawberry starter material. However, Kars indicates that the technique is now being applied to other crops as well. "We are also treating raspberry plants, including both root blocks and long cane plants. We are seeing positive results here, and we will share official research findings later." Moleda is also making tentative steps in ornamental crops. "Here, we see it being used as a form of export protection."

Cas with customers in South Africa

Fungi, Pests, and Bacteria
The list of fungi, bacteria, and pests that can be treated is extensive, but there's always room for improvement. "Importantly, we have ensured that 99% of strawberry plants survive the sauna treatment. We have successfully treated all the common known species in Europe and North America."

For some pests, such as whitefly, reduction has been observed after treatment. However, Kars emphasizes that scientific research is needed before Moleda can make any official claims. "Any additional reduction of pests like whitefly, aphid, or thrips is already a welcome bonus for users.

A Clean Start
The team at Moleda is proud to offer users an extra option in their Integrated Pest Management (IPM) strategy with Plantsauna. "We help growers start as cleanly as possible. This makes us a small but crucial component in the larger IPM strategy."

With the current capacity, users can treat around 30,000 to 35,000 plants per pallet with one Plantsauna, processing three pallets per day, 24/7. While scaling up capacity was considered, it proved challenging to maintain 100% certainty of equal temperature treatment. "For those needing more capacity, it's best to install additional Plantsaunas. One US user already has seven. The benefit of having multiple units is increased flexibility and the ability to stagger planting of the treated plants."

A row of Plantsaunas at a customer in California.

The following fungi, pests and bacteria can be treated with the Plantsauna:

  • Strawberry mite/ Cyclamen mite (Tarsonemus Pallidus)
  • Stem base rot (Phytophthora Cactorum)
  • Anthracose/black fruit rot (Colletotrichum acutatum)
  • Powdery mildew (Podosphaera aphanis)
  • Angular leaf spot (Xanthomonas fragariae)
  • Grey mould (Botrytis Cinerea)

For more information:
Kars Vreeswijk
+31 6 29297390
[email protected]
[email protected]

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