4/6/2020 - By Lynn Griffith

As a human population, we’re currently battling an invisible enemy - a virus. It’s an unprecedented time, and we should be very grateful for all of those that are committing themselves to the situation at hand. We’re not the only ones susceptible to viruses though. Did you know that plants have to contend with viruses too? Well, they certainly do, and if growers don’t put in the work to protect their plants from viruses, they can have some devastating effects, as in the case of Tomato Spotted Wilt Virus (TSWV). 

What is a virus anyway? A virus is basically a section of RNA or DNA, genetic material surrounded by a protein coat. Viruses are primitive, microscopic organisms, and they can’t reproduce on their own. They basically enter the cells of plants, animals or bacteria and trick the cell nuclei into running off copies of more viruses - a dastardly little trick.

In general, plant viruses are named after the first plant type within which they are discovered and their associated symptoms. Tobacco Mosaic Virus, which causes mosaic-like mottling and discoloration to infected tobacco leaves, is a classic example. Some viruses can even receive more than one name, depending on which crops they infect. They can be transmitted (vectored) from crop to crop by insects, like thrips, or by touching & pruning, known as mechanical transmission. 

Tomato Spotted Wilt Virus has been around for over 100 years, but don’t let its name fool you. It’s actually an RNA virus known to attack over 100 types of plants in 85 different plant families. You might find TSWV on potted crops such as mums, gloxinia, cyclamen and gerbera, cut flowers like zinnia and peony or even annuals like petunia, marigold and impatiens. Vegetables such as potato, celery and spinach are also vulnerable to the virus, and it can be easy for foliage plants like Bird’s nest fern, dracaena and syngonium to fall victim to its infection. It also targets numerous perennials and a variety of common weed species. 

TSWV is commonly spread by 9 different types of thrips, especially Western Flower Thrips. Early on, thrips nymphs acquire the virus, but they don’t infect the host plant until later during their adult stage when feeding on the plant. Adult thrips can live for 30-45 days, during which time they can lay 150-300 eggs; that makes for quite a formidable opponent! Symptoms of infection vary quite a bit by plant species, but they can include ringspots, black streaks, necrotic spots and tip dieback. Many labs can also test for the virus. 

Pictured: Thrips injury on roses

To get ahead of TSWV, growers need to stay on top of thrips. Some ways to do this include disposal of infected plants, weed control, use of yellow sticky traps, biological control agents and chemical controls. There are at least 4 biocontrol options, and chemical control options include Conserve, Avid, Orthene, Tristar, Azatin, Talstar, Decathlon, Pedestal, Pylon, Safari, Scimitar, and Imidacloprid. Flagship and Mainspring are also popular, as are some of the oil suffocants. Your growing region will determine which specific control options, or combination thereof, will work best to defend against these uninvited guests. 

Tomato Spotted Wilt Virus has been around since 1914, so we’ve had a lot of time to develop defenses against it. Consider your biocontrol options, keep your weeds under control and talk to your Harrell’s representative about the best chemical options for controlling your thrips. By covering all your bases, you can ensure your plants have the most robust virus protection plan.