The Dutch horticulture is alert for the risk of the Tomato chlorosis crinivirus (ToCV). The virus has so far been found at eleven Dutch tomato production companies. A survey of other production companies, including tomato but also pepper, and eggplant, is conducted and growers are advised to take extra measurements against whitefly and tobacco white fly. The monitoring and advising team of the committee TuinbouwAlert also advises petunia growers to watch out, since this crop can also be contaminated with the virus.
First time contamination
In November/December 2017 tomato chlorosis virus (ToCV) was discovered at three tomato cultivation companies. The origin of the ToCV infections is unknown. By now, the virus has been found at eleven tomato greenhouses. It is the first ToCV outbreak in the Netherlands and in Northern-Europe, but in other, southern EU countries it is quite a common disease. In Netherlands though everything is tried now to eliminate the virus. "Now is the time to do so, now we still have the chance", is the vision of the NVWA, the Dutch Food and Consumer Product Safety Authority.
The virus is not specifically listed as a harmful organism in the EU directive 2000/29/EC, however it concerns a virus that can be transmitted by Bemisia tabaci, and as such is listed in annex IAI of Council Directive 2000/29/EC. The virus is established in several EU member states where it is not known to be subject to official measures. Once infected, there will be no total crop failure, but production will go down and the crop may be more susceptible to other viruses.
Controlling white fly
The tomato chlorosic virus (ToCV) is transmitted by the adults of the white fly Trialeurodes vaporariorum and Bemisia tabaci (tobacco white fly). The virus is not transmissible to seed and can not be transferred with material. The symptoms, yellow discolouration between the veins, are visible only four weeks after infection and can easily be confused with deficiency symptoms of magnesium.
The tomato chlorosic virus (ToCV) is transmitted by the adults of the white fly Trialeurodes vaporariorum and Bemisia tabaci (tobacco white fly). The virus is not transmissible to seed and can not be transferred with material. The symptoms, yellow discolouration between the veins, are visible only four weeks after infection and can easily be confused with deficiency symptoms of magnesium.
ToCV relatively quickly transmitted. White fly can transmit the virus within an hour during feeding, but it gets more effective the longer the white fly feeds on the crop. To prevent further spreading, controlling white fly is very important. Due to the declining resource package, chemical control is no longer an option. There must therefore be full attention to monitoring, measures and organic control of white fly. It is recommended that all other (greenhouse vegetable) companies keep the population pressure of white fly as low as possible.
As of the findings last year, the NVWA has been conducting research among tomato companies into the presence of plants that are infected with the ToCV. Now several more contaminations have been found, the research is expanded to other crops since also pepper and eggplant crops can be infected with the virus. If plants infected with ToCV are found in a company, an elimination scenario is enforced.
Monitoring and controlling white fly
To prevent further spreading, controlling white fly is very important. Due to the declining resource package, chemical control is no longer an option in the Netherlands. The team of TuinbouwAlert therefore advises: "There must therefore be full attention to monitoring, measures and organic control of white fly. It is recommended that all other (greenhouse vegetable) companies keep the population pressure of white fly as low as possible."
For monitoring the weekly maintenance of 20 traps per ha is recommended. "This keeps the course over time and throughout the greenhouse in oversight. One hanging trap per path should also catch the white fly as much as possible. If there is more than one greenhouse at one location, it is important to ensure that the white fly doesn't move from one department to another via product, packaging or people."
The main organic weapon is the predatory bug Macrolophus pygmaeus. They have to be introduced to the cultivation as early as possible to reach a good population build up. "If possible, distribute them at the nursery. Macrolophus pygmaeus deals with all stages, with a preference for eggs and larvae of white fly and Bemisia. At least six bugs per stalk are desirable for good control. Additionally, the parasitic wasp Eretmocerus eremicus should be used with 6/2m against 2nd and 3rd stage larvae of white fly and Bemisia. If this is still insufficient, there is the option for overkill with 12 parasitic wasps per m2."
In addition, the insect parasitic fungus Lecanicillium muscarium (such as Mycotal) has a good effect by using it on a weekly basis. The chemicals Admiral or Oberon can also be sprayed, however the possibilities in the Netherlands for this are very limited (twice per cultivation).