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Plant and Pest Advisory – Andy Wyenandt – September 13, 2024
Tomato spotted wilt virus (TSWV) has caused significant problems for some fresh-market tomato and
pepper growers in New Jersey the past few growing seasons. Although not uncommon, economic
losses these past few years have been extensive on some farms.
TSWV is vectored by various species of thrips, a common vegetable insect pest that seems to
be on the incline and very difficult to control in vegetable production throughout the state. The
most important vector of TSWV is the western flower thrips, Frankliniella occidentalis. It’s mode
of transmission is persistent propagative, meaning that thrips nymphs have to feed on an infected
plant, whereby followed by a short incubation period (lasting from hours to days), the virus is then
persistently transmitted throughout the rest of the insect’s life span.
TSWV cannot be passed from infected females to eggs; and TSWV is not transmitted in seed.
The western flower thrips and TSWV both have a wide host range! Western flower thrips host
range includes: tomato, pepper, onion, celery, cucumber, lettuce, potato, basil,strawberry; a wide
range of herbaceous ornamentals (e.g., impatiens, geranium, marigold,petunia, dahlia, gerbera
daisy, carnation) as well as many common weeds (e.g., pigweed,chickweed, lambsquarter, thistle,
galinsoga). TSMV can infect over 1,000 plant species from more than 90 plant families.
In California and other tomato production regions, resistance-breaking (RB) strains (C118Y,C118F,
T120N) of TSWV have recently been discovered that can overcome the single gene resistance
(Sw-5b) bred into widely-grown processing and fresh-market tomato varieties. Recent research in
Texas has also shown that RB TSWV strains may increase western flower thrips fitness (ability to
reproduce) by prolonging the adult period and increasing fecundity (i.e., a measure of an insect’s
reproductive success, often expressed as the number of eggs or offspring produced by an insect)
compared to non-RB and non-viruliferous controls. Unfortunately, the breakdown of genetic
resistance along with the potential increase in TSWV-infected thrips reproduction rates, may lead to
significant problems in thrips and TSWV control in New Jersey and elsewhere.
Recent work in Texas has shown that RB-TSWV can break resistance (conferred by the commonly
deployed TSW-mediated single gene resistance) in TSWV-resistant pepper (Capsicum annuum) with
varying levels of symptom development in both resistant and susceptible cultivars; with none being
completely immune.
In October 2022, samples of a TSWV-infected fresh market tomato variety with Sw-5b resistance
were collected in southern New Jersey and sent for analysis. Results determined that RB (C118Y)
TSWV was present in the state; and the strain found in New Jersey was similar to the RB TSWV
found in fresh-market tomato from Mexico and processing tomato in California suggesting a high
potential for its widespread movement.
So, where do we go from here? Based on the isolated report of TSWV being found on resistant fresh market tomato in New Jersey in 2022, and the more recent reports of it this year, it does not appear
that RB TSWV is currently widespread throughout the state. However, this may likely change.
All vegetable growers, those who produce their own transplants or bring them in, need to carefully
evaluate their thrips monitoring and mitigation programs this winter.
1. Start fresh. Prior to the transplant production season, clean and disinfect the greenhouse or any
other structure where you might be holding transplants. Remove any weeds within and around the
structure. Use sticky cards to monitor the potential carryover thrips population during the winter
months, especially if you have any plant material in the greenhouse during those months.
2. Never produce or keep tomato or pepper transplants you start yourself or bring in, in the same
greenhouse with any ornamental plants.
3. Segregate any transplants that are brought into your operation from your own transplants, as well
as segregate different source of transplants as best you can.
4. Evaluate all incoming transplants for thrips damage.
5. Treat all incoming transplants with an insecticide immediately.
6. Use yellow sticky cards to continually monitor for thrips populations in the greenhouse
from the start of the transplant season until the end.
7. Consider using biological or natural control(s) in the greenhouse.
8. The use of silver reflective mulches have been shown to reduce thrips populations in fields.
9. Develop a season-long insecticide program prior to the production season; from applying an
insecticide at transplanting through cover sprays until harvest.
10. Monitor thrips populations and feeding damage in the field with regular scouting and sticky cards.
11. Closely monitor thrips feeding injury on pepper and tomato fruit during the production season.
12. Proper weed control is essential since many weeds may harbor the virus or infected thrips. This
includes areas around the production field.
13. Rogue out any suspicious looking plant(s) prior to transplanting, or any suspicious looking plant
early in the production season (e.g., any plant that starts to stunt out early) to help mitigate the within
field spread.
Growers should continue to utilize TSWV-resistant tomato and pepper varieties realizing the
effectiveness of those in limiting TSWV is becoming compromised. All growers need to continue to
follow best management practices (such as those listed above) and pay careful attention to current
weaknesses in their production practices and thrips control programs and adjust their management
practices heading into 2025 growing season.
by: Andy Wyenandt and Kris Holmstrom
References: Macedo MA, Melgarejo T, Cespedes M, Rojas M, Lazicki P, Turini T, et al. (2024) An allout
assault on a dominant resistance gene: Local emergence, establishment, and spread of strains
of tomato spotted wilt orthotospovirus (TSWV) that overcome Sw-5b-mediated resistance in fresh
market and processing tomatoes in California. PLoS ONE 19(7):e0305402.
Tomato spotted wilt virus on pepper and tomato. Inga Meadows and Andy Cooper, NCSU 2024.
Gautam et al., 2022. First report of a resistance-breaking strain of tomato spotted wilt orthotospovirus
infecting Capsicum annuum with Tsw resistance gene in Texas. Plant Dis.107:1958.