Tomato spotted wilt is a widespread plant disease that can severely impact crops and ornamental plants. While its name mentions tomatoes, it affects many plant species, challenging gardeners and agricultural producers. Understanding its nature and symptoms is the first step in protecting plants.
Recognizing the Signs
Plants infected with tomato spotted wilt display distinctive symptoms that vary by plant species and infection stage. Young leaves develop bronzing on upper surfaces, progressing to small, dark necrotic spots. Leaves may also cup downwards, and plants might experience tip dieback.
Beyond leaves, infected plants often exhibit stunted growth and brown streaking on terminal stems. On fruits, especially tomatoes and peppers, yellow ringspots or brown, sunken necrotic areas often appear as concentric rings. Early infection can lead to total fruit loss, while established plants may show decreased yields and deformities.
Understanding the Virus and Its Carriers
Tomato spotted wilt is caused by the Tomato Spotted Wilt Virus (TSWV), a Tospovirus. The virus is characterized by its spherical, enveloped virion containing three single-strand RNA segments. It replicates within infected plants, making them a source for further spread.
TSWV primarily spreads through tiny insects called thrips. At least 10 thrips species can transmit TSWV, including the western flower thrips (Frankliniella occidentalis) and the tobacco thrips (Frankliniella fusca). Thrips acquire the virus during their larval stage by feeding on an infected plant; it then replicates within their salivary glands. Adult thrips transmit the virus to healthy plants as they feed, remaining capable of transmission for the rest of their lives.
Preventing and Controlling Its Spread
Managing tomato spotted wilt requires a multi-faceted approach, as there is no cure. Promptly removing and destroying symptomatic plants prevents further spread. Controlling weeds in and around garden areas is also important, as many can host both the virus and thrips.
Choosing resistant plant varieties, when available, offers proactive defense. For instance, some tomato cultivars possess the Sw-5 resistance gene. Monitoring thrips populations with sticky yellow traps aids early detection and management. If thrips populations are high, insecticidal soaps or neem oil can be applied, especially early in the season, to reduce numbers. Good garden hygiene, such as cleaning tools and avoiding overhead watering, also minimizes spread risk.
Host Range and Broader Implications
Despite its name, Tomato Spotted Wilt Virus has a broad host range, infecting over 1,000 plant species across more than 85 plant families. This includes vegetables like peppers, potatoes, and lettuce, as well as many ornamental plants and common weeds. The virus can affect both dicotyledonous and monocotyledonous plants.
This wide host range makes it a widespread and economically impactful plant disease in agricultural settings and home gardens. For example, Georgia alone experienced an estimated annual average loss of $9 million in tomato and pepper crops due to TSWV between 1996 and 2006. Its prevalence and ability to infect many plant types make it a persistent global challenge for plant health.