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Tomato spotted wilt virus (TSWV)

TSWV has been occurring more commonly on Long Island recently in tomato as well as some other crops, including potato, pepper, and eggplant.  So far impact has not been substantial except when symptoms began appearing on transplants.  TSWV can stunt and kill plants when infection occurs early.  Symptoms on leaves can vary partly due to plant age at the time.  Symptoms usually start to develop at the top of plants.  Upper leaves develop large areas that are dark brown to black, more often at the leaf base, with occasional ringspots.  Stems and petioles often have dark brown areas.  Growing points can be killed.  Symptoms developing on fruit renders them unmarketable.  Brown discoloration on green fruit is the most common symptom.  Affected fruit tend to drop off the plant.

Western flower thrips, an important vector, has been occurring more commonly on Long Island.  Resistance to insecticides has made their control more difficult.  It is difficult to manage TSWV by managing thrips because of how quickly virus can be transmitted when thrips feed.

Several TSWV-resistant tomato varieties are now available.  Most were developed for the southeastern region because TSWV has been a consistent constraint on production there.  A list of TSWV-resistant varieties that have performed well in evaluations conducted in FL and GA can be found on the USDA Tomato Spotted Wilt Virus RAMP Project webpage.   Degree of resistance can vary among varieties because performance of resistance genes can be affected by host plant background.  There is concern about appearance of a new strain of TSWV able to overcome the resistance.

An important management practice is not growing tomato transplants in the same greenhouse as ornamental plants because the virus has a very wide host range.  Destroy affected plants so they do not serve as a source of virus for other plants.

There are other orthotospoviruses (aka tospoviruses) causing symptoms similar to TSWV that are also of concern on Long Island.  Groundnut ringspot virus (GRSV) and Tomato chlorotic spot virus (TCSV) were discovered more recently than TSWV.  Both have been detected to a limited extent on LI.  TCSV is especially of concern because it has become the dominant virus on tomato in FL and has caused substantial losses.  See news article for information about it.

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Below:  Ringspots caused by TSWV and white spotting due to feeding by Western flower thrips which vector this virus.

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Below: Symptoms that developed on seedlings while growing in a greenhouse.

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