Based on all the measures that are taken to prevent the spread of the Tomato brown rugose fruit virus (ToBRFV), you would expect that the virus wouldn’t be able to spread any further. The opposite seems to be the case, now the virus has spread more in the Netherlands than expected and hoped.
"Apparently, there are other reasons why ToBRFV can penetrate greenhouses," Kees Luykx of Luykx Ultrasound concludes. "One of the most obvious causes is via irrigation water. Every grower knows that irrigation water is a very large source of contamination. And ToBRFV can survive in water for a long time, as is also mentioned in the strict Hygiene Protocol (Dutch)."
Nowadays, all possible hygienic measures are applied to keep pathogens outside the nursery. Tomato growing companies in particular, have almost changed into hospitals looking at the measures that are being taken, from disinfecting of shoes, fending off everyone who has nothing to do with the company up to the obligated donning of special clothing and sterilizing of (harvesting) tools. But irrigation water? Kees believes that there is not enough attention for that yet.
Source of contamination
"Via the irrigation water and drip system, many cubic meters of water are pumped into the greenhouse every day. Normally this water is taken from the basin and passed through a UV disinfectant. There is no pathogen control in the basin, so pathogens are present in the basin water in large quantities.
Spread of pathogens (ToBRFV) from basin to basin can easily be done by ducks, birds and other smaller animals. That almost all pathogens occur in the basin water is not only inconceivable, but rather likely," Kees says."If that is the case, there is a large source of contamination close to the greenhouses."
25 million ToBRFV viruses per cubic meter of water
Despite the fact that a lot of water passes through a UV disinfectant, Kees points out that this cannot fully be relied on. "Laboratories generally maintain a margin. If after the disinfectant there are less than a few tens of fungi per milliliter, this disinfectant is considered to be working properly.
Because viruses are even more difficult to control than fungi, it is not illogical to maintain this value for viruses as well. Some laboratories conclude that when less than 25 colony forming units (cfu) of fungi per milliliter occur, the disinfectant is performing well. Assuming that the same numbers apply to viruses, this however comes down to 25 million viruses per cubic meter," Kees points out.
With every cubic meter of water that enters the greenhouse, 25 million fungi or viruses can enter with it. This is seen as safe. Anyone can imagine that this cannot be true, pumping 25 million ToBRFV viruses per cubic meter of water into the greenhouse cannot be safe. If such a situation occurs only once during a cultivation, the entire greenhouse may be contaminated and remains so until everything is cleared and disinfected."
Another possibility of contamination is when insects become infected with ToBRFV when coming into contact with basin water. "Those insects then may end up in the greenhouse and infect the crop. This direct contamination does not go through a UV disinfectant or whatever means and is therefore uncontrollable."
Keep water clean permanently
According to Kees, a good solution for these large, water-related contamination risks is the permanent treatment of water resources in the basin or silo. "By ensuring that the basin water contains as little as possible or no fungi or viruses at all, the chance of contamination is also as small as possible. In addition, the after-treatment of the water by the UV disinfectant is much less critical, because there are far fewer fungi/viruses left in the water."
Luykx Ultrasound has developed a combination unit of ultraviolet light and ultrasonic sound for water treatment in a basin or silo. "This USAF-UV unit continuously treats the water, so that the unwanted pathogens are controlled permanently. The unit can be placed very easily in the basin or in the silo and is virtually maintenance-free."
If a USAF-UV control system is installed in all basins, mutual contamination between basins is no longer or a much smaller problem, Kees concludes. "New pathogens will always appear, so fighting them in the water storage is a necessity not to have to fight a specific new fungus or virus. The USAF-UV unit fights all pathogens preventively, 24/7."
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