A greenhouse-grown chrysanthemum was received in the Plant Disease and Insect Clinic on July 10th and diagnosed with Tomato spotted wilt virus (TSWV) by Emma Lookabaugh. Symptoms consisted of dark leaf spots, lateral curling of the leaves at some of the spots, and at least one stem lesion.
|TSWV symptoms on Chrysanthemum|
Although TSWV is the most commonly diagnosed viral disease here in the PDIC, it has been a long time since we've detected it on chrysanthemum from North Carolina. We have no records of it during the current millennium, but if memory serves there was at least one case back in the late 1990s. The current case does not constitute an outbreak, but should serve as a reminder to growers to take measures to prevent this disease.
|A different sort of TSWV symptom on mum, from a different sample.|
|Mottling and ringspot symptoms on TSWV-infected Senecio (left) and Stokesia (right)|
|A thrips compared to the tip of a pin.|
- Avoid growing vegetable transplants and flowers in the same greenhouse, and avoid growing plants of different ages together.
- Screen greenhouse vents and air intakes to exclude thrips from entering the greenhouse.
- Control weeds in and around the greenhouse. Many weeds are susceptible to tospoviruses and can serve as reservoirs of virus and thrips.
- Monitor greenhouses for thrips activity using blue or yellow sticky cards, with the top 2/3 of the card placed above the plant tops. Use two cards per 5000 sq. ft. of greenhouse area.
- Use insecticides to manage thrips populations when necessary. Remove flowers from plants before treatment since the interior of flowers rarely get adequate coverage. It is important to note that some thrips populations have developed insensitivity to commonly used insecticides. In addition, no insecticide can completely eliminate thrips. Utilize the most effective chemistries wisely by rotating insecticides by mode of action (IRAC class) with each application, or at least with every generation of thrips. Always follow label directions and check that products are labeled for the intended crop. Details on insecticides for thrips management can be found in the NCSU Information Note on Western flower thrips and the University of Florida's thrips management information.
|TSWV symptoms on Lobelia|
More information about TSWV in the following crops is also available:
Mike Munster and Steve Frank
*Grammatical footnote: The word thrips is both singular and plural.
**Mention of trade names and companies does not imply endorsement by North Carolina State University or the Plant Disease and Insect Clinic.