Virus issues? Take a look at transplant production.

Author: Marissa Schuh, Integrated Pest Management Extension Educator,

University of Minnesota Extension.

Many commonly grown Minnesota vegetables can be infected by plant viruses.  With their limited means of prevention and no control options post-infection, these diseases can be devastating.  Solanaceous crops, especially peppers and tomatoes, can play host to over a dozen plant viruses.  These viruses stunt plants, distort leaves and fruit, and severely reduce yield.

Virus damage as extensive as this often starts during transplant production, where entire trays can be exposed to plant viruses. Photo: Marissa Schuh, UMN Extension.

If you’ve experienced severe losses to viruses in the past, it is worth taking a look at your plant sources.  Depending on the virus, the greenhouses where transplants are produced can serve as a key site of infection.  Many tomato and pepper viruses are vectored by tiny, heat-loving, quickly-reproducing insects like aphids and thrips.  

An entire tray of pepper transplants showing symptoms of viral infection (stunted new growth, distorted and crinkled leaves). Photo: Natalie Hoidal, UMN Extension.

When these insects feed on a virus-infected plant, they pick up the virus, and then transmit it to new plants as they move through the greenhouse and feed on other plants.  Many of these viruses can infect a wide range of plants, including ornamentals and weeds.  These alternative host plants may show no symptoms, while the solanaceous crop can be devastated.

Western flower thrips can easily go undetected in greenhouses. Photo: David Cappaert, Bugwood.org

Managing these tiny pests in the greenhouse is hard! They are small, can enter greenhouses undetected, and grow their populations quickly.  It also only takes a single feeding event by a single insect to vector a virus to a new plant.   This means controlling them with pesticides is incredibly difficult, and biocontrol programs are complex to implement.

A more effective way to combat virus issues is to limit the potential sources of plant viruses.  Ornamentals, weeds, and perennials grown in the same greenhouse can serve as a source of viruses.  If viruses have caused major issues, look at what you can do to separate these plants to limit virus reservoirs.

Yellow sticky cards can be used in the greenhouse to monitor for pests. Photo: Rachel McCarthy, Cornell University, Bugwood.org

If you can’t avoid growing ornamentals and vegetable transplants in the same space, it is important to prevent and monitor these small insects.

• Inspect incoming plant material for insects.

• Use yellow sticky cards to monitor for insects.

• Visit the Greenhouse IPM page for information about managing pests.

If you do see viruses in transplants, dispose of those transplants.  Again, they will serve as a source of the virus.  They are also unlikely to produce anything marketable if planted.