4 tips for identifying and preventing viral diseases in the greenhouse

All photos courtesy of Dr. Beth Scheckelhoff, OSU

Plant viruses are serious pests of ornamental and edible crops alike and cause significant losses for greenhouse producers. Once infected, a plant will remain infected with the viral disease throughout its lifespan — and may pass the virus along to progeny. There are no chemical or biological products that cure plants infected with a virus.

Instead, prevention is key for successful management of viral diseases in greenhouse crops.

Growers and greenhouse employees should be able to recognize common signs of plant viruses. Viruses can cause unusual physical characteristics like mosaic patterns, ringspots, mottling, leaf distortion, stunting and yellowing, among others (Figures 1, 2, 3 and 4). While these symptoms may also result from other issues like nutrient disorders, other pests or even unique attributes like variegation or speckling, training employees to spot usual versus unusual characteristics for a particular plant will help diagnose and correct many production problems. In some cases, infected plants may show no symptoms and evade detection.

Here are four tips to staying disease free to share throughout your growing operation:

Start virus-free

Plant viruses can infect greenhouse crops in many ways. Viruses can come in on plant material — from seeds to cuttings, plugs and/or mature plants. A grower’s first line of defense is to begin with virus-free plant material. How can you start with virus-free plants?

Choose varieties or cultivars that have genetic resistance to common viruses, when possible. Many food crops and a limited number of ornamental crops have genetic resistance or increased tolerance to one or more viruses.

If resistance packages are not available for specific plants, purchase certified virus-free seed, cuttings or plantlets.

When neither of these options are available for the plants you grow, quarantine incoming plants and train all employees to look for unusual symptoms that may be present or develop over time.

Manage viral vectors, too

Thrips, aphids and leafhoppers are well-known vectors of plant viruses in ornamental plants. Monitoring and controlling insect populations are key strategies to prevent virus transmission (Figure 5).

Here are some tips to exclude common vectors of plant viruses:

• Install exclusion screens to keep insects out of growing environments.
• Remove weeds and volunteer plants from in and around greenhouses, retail areas and buildings (Figure 6). Many viruses can be found in a wide range of host plants — including weeds, native plants, agronomic and vegetables crops, and ornamentals. These alternate hosts serve as reservoirs for viruses.
• Grow trap crops to attract insects such as thrips and aphids. Regular monitoring of these plants will alert you insect pressure before reaching more sensitive crops.

Halt mechanical spread

Viruses can also spread mechanically from our clothing, hands and tools through routine practices like pruning, deadheading, propagation and handling of plant material. Routine and frequent disinfection of tools can help prevent spread.

Employees should also routinely wash and sanitize their hands when directly handling plant material, especially those suspected of having a virus.

Remain virus vigilant

Continue scouting in the greenhouse throughout the growing season, removing suspect plants as they are found. Once plants are infected with a virus, they cannot be cured — but can serve as a reservoir from which other plants become infected. Remove and discard diseased plants.

Bonus tip: need confirmation?

Suspect plants can be sent to diagnostic clinics across the U.S. Unsure of which universities have a diagnostic clinic? Check the National Plant Diagnostic Network website (npdn.org) to see plant diagnostic clinics in regions across the U.S. It is a good idea to contact the diagnostic clinic of your choice to determine their virus testing capabilities. In some instances, plant samples may be directed to another facility for more comprehensive testing.

This e-Gro alert was originally published March 2022 in Volume 11 (2022).

Dr. Beth Scheckelhoff is an extension educator, agriculture and natural resources, with The Ohio State University Extension Putnam County. She can be reached at scheckelhoff.11@osu.edu.