Everyone has become more knowledgeable about the spread of viruses and the diseases they cause. Just like the COVID virus, we have to understand the life cycle of each virus that cause diseases in greenhouse crops. Effective virus disease control requires controlling or shutting down three important links; the source of the virus, the vector of the virus and the host plant.

Viruses cannot live on their own for long. They need a host, such as a plant or insect. The main source of viruses is infected plant propagation material. If a plant is infected, all parts will contain the virus. Plant residue (also referred to as volunteer plants), no matter how small, can be a source of viruses. Plant residue is usually pant material left from previous plantings. It is usually a factor where more than one planting is made in a season or where successive crops are grown in one structure. Any plant material left on the ground after harvesting is a potential source.

Since a virus cannot move on its own, it needs a vector to Uber it around. Tomato spotted wilt virus can survive long periods in its host. So the vector can spread the virus long distances. Infected pupae that survive a whole season in the ground will also infect the plants in the new season.

Viruses live in weeds and ornamental plants that are often planted around greenhouses and alongside roads. It is recommended to plant various plants that are hosts to predator insects to pests, but these plants may be infected with a virus. They do not infect the predator insect, as they do not feed on plants. But they will infect the pest feeding on the infected weed or ornamental plant.

The nutrient solution of a hydroponic system can be a source of viruses. They can survive for six months in the water.1)Pares, R. & Gunn, L. & Cresswell, Geoff. (2008). Tomato Mosaic Virus Infection in a Recirculating Nutrient Solution. Journal of Phytopathology. 135. 192 – 198. Some growers have balancing tanks. These are often larger than 20,000 L and nutrient effluent are pumped into these thanks and re-used, thus spreading the virus to other parts of the growing system.

References

References
↑1 Pares, R. & Gunn, L. & Cresswell, Geoff. (2008). Tomato Mosaic Virus Infection in a Recirculating Nutrient Solution. Journal of Phytopathology. 135. 192 – 198.