How to manage plant viruses in the greenhouse
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EmailInsect management is critical for managing tomato spotted wilt virus and impatiens necrotic spot virus, while sanitation is the critical management strategy for tobacco mosaic virus.
In "Common types of viruses of floriculture crops and their modes of transmission," Michigan State University Extension reviewed the background about some of the most common viruses that affect floriculture crops: tobacco mosaic virus, tomato spotted wilt virus and impatiens necrotic spot virus (Photos 1-3). Details of insect transmission of Tospoviruses were explained. The type of virus and its method of transmission impact the methods of management that should be implemented when a virus is detected on plants in a greenhouse.
Photos 1-3. Symptoms of tobacco mosaic virus on Tradescantia or wandering Jew (left), tomato spotted wilt virus on Osteospermum (middle), and impatiens necrotic spot virus on marigold (right). Photos by Jan Byrne, MSU.
Growers should inspect all incoming plant material for symptoms of viruses, including speckling, modeling, leaf curling, vein clearing, chlorosis and stunting. Unfortunately, viruses can be present in plants that are asymptomatic or may not show symptoms for weeks after infection. If there is a known possibility of infected plant material coming into your facility, be extra vigilant when inspecting the plant material and randomly sample plants within each shipment and variety.
Virus testing supplies for rapid in-house testing are available to purchase. This allows growers to easily test suspect material identified during scouting. Plants with ambiguous symptoms can yield a positive test result. Alternatively, samples can be sent to a local diagnostics lab, such as MSU Plant and Pest Diagnostics. Continue to scout the plants during the crop cycle. If possible, quarantine the susceptible or suspicious plant material. If plants test positive for viruses, immediately throw them out as virus-infected plants cannot be cured.
When there is a virus present on plants in the greenhouse, sanitizing benches, floors, watering wands and any other equipment that may come in contact with plant material is critical. Be sure to remove all weeds under any benches in the greenhouse. The primary method of spread of tobacco mosaic virus is by plants touching each other or by hands carrying the virus after touching infected plants. It is critical that those who are touching the plants are regularly washing their hands with soap and water and after touching any suspicious plants or using tobacco products.
When sticking cuttings or transplanting plugs, make sure the plants are only touching non-permeable surfaces and regularly sanitize all surfaces the plants make contact. All employees sticking cuttings should regularly use an alcohol-based hand sanitizer. MSU Extension recommends using a fresh solution of the disinfectant; be sure that the active ingredient of the product is stable enough to remain active while using it throughout the day.
Soaking areas is likely to be more effective than a spray or spritz application. Some growers use diluted dry milk, which has been shown to be effective in disinfecting tools and surfaces. Spraying milk directly onto plants to prevent virus transmission has also been shown to be effective. To read more about research findings with using milk as a disinfectant, read “Can applying milk to tools or plants be effective in reducing virus transmission?” For more information on other sanitation strategies, read “Sanitation Strategies for Greenhouse Growers.”
When trying to manage an occurrence of Tospoviruses (e.g., tomato spotted wilt virus or impatiens necrotic spot virus), managing aphid, whitefly and thrip populations are critical. As discussed in "Common types of viruses of floriculture crops and their modes of transmission," these viruses are readily spread by insects. Western flower thrips are one of the primary vectors of these viruses. For thrips control, refer to the Greenhouse Insect Pest Management Guide.
For more information on how to manage tomato spotted wilt virus or impatiens necrotic spot virus, visit “Impatiens Necrotic Spot Virus” from PennState Extension.
Insect control is not as critical in an outbreak of tobacco mosaic virus because insects are not the main vector of the virus. However, according to H.J. Walters, chewing insects like grasshoppers can vector tobacco mosaic virus, but those are not common in greenhouse production. Okada et al. reported that tobacco mosaic virus could be spread to non-infected plants by bumble bees after pollinating heavily infected plants. Also, if infected leaves have exposed sap or if insects break leaf hairs, aphids have been shown to be a possible vector of tobacco mosaic virus, but it is not a major method of spread.
For more information on tobacco mosaic virus, read “Tobacco Mosaic Virus of Tobacco” from North Carolina State Extension.
To learn more about tomato spotted wilt virus, tobacco mosaic virus, or impatiens necrotic spot virus on a greenhouse crop, see “Common types of viruses of floriculture crops and their modes of transmission.”
The author would like to thank Dave Smitley, Zsofia Szendrei and Jan Byrne for their reviews.
The author would like to thank Dave Smitley, Zsofia Szendrei and Jan Byrne for their reviews.
