Symptoms and management strategies for impatiens necrotic spot virus
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Impatiens necrotic spot virus (INSV) is transmitted by thrips and can cause disease on greenhouse crops (view photos). Since this virus can infect more than 300 species, it is critical to know the crop species at risk and the symptoms associated with infection. Although ring spots, such as those that commonly occur on cyclamen, impatiens, cineraria, gloxinia and begonia are among the best know symptoms caused by INSV, ring spots may not occur on all infected species.
INSV affects bedding plants, with impatiens and begonias being especially at risk of infection. The most common symptom of INSV infection on impatiens is dark purple ring spots on the leaves. Dark streaks on the stems or leaves may also occur. Yellowing of the foliage and development of “strap-like” leaves often accompany ring spotting and streaking. On begonias infected with INSV, mottling, mosaic and patchy, irregular brown and dead (necrotic) areas are commonly seen. Symptoms of infection by INSV on other bedding plants may vary. Frequently observed symptoms of infection include spotting, patchy and irregular brown and necrotic areas, mottling/mosaic and ring spots. Symptoms including yellowing, distortion, and stunting are not always common. Bedding plants infected with INSV may have a negative impact on the vegetable industry, because, according to a survey, greenhouse-grown transplants of peppers, lettuce and tomatoes were infected with INSV.
Potted plants/hanging baskets
INSV has caused devastating plant death in crops of cyclamen, cineraria, New Guinea impatiens and gloxinia. On cyclamen, the most distinctive symptom of INSV is a thumbprint-like yellow ring spot on leaves. Flower petioles may also be distorted with brown streaks. Symptoms of INSV on cineraria include faint ring spots or blotches on the leaves that gradually darken. Black streaks may occur on petioles and lower leaves may wilt and die. On gloxinia, browning of the midrib or crown of the plant, followed by collapse and plant death is common. New Guinea impatiens infected with INSV may not show disease symptoms or may die back and collapse as a result of a black stem canker. Stunting, dark leaf spots or distortion of the foliage may also occur on New Guinea impatiens infected with INSV.
On other potted plants and hanging baskets, generalized browning and necrosis are symptoms of disease caused by INSV. Other symptoms often seen include ring spots and chlorotic/necrotic spots. Less commonly seen symptoms include mottling/mosaic, distortion, chlorosis and stunting. Infected plants showing only mild disease symptoms may escape detection and provide inoculum for other plants. For instance, infection by INSV may result in either no symptoms or only mild disease symptoms on Thanksgiving cacti. In one commercial greenhouse, Thanksgiving cacti infected with INSV served as a common denominator for two nonoverlapping gloxinia crops that were infected with INSV. Several genera of potted plants are asexually propagated and unrooted vegetative cuttings for potted plant production are imported in significant numbers. Visual symptoms alone may not be adequate for detection of INSV in propagative material.
Differences in susceptibility among plant species are not immediately evident on foliage plants. Spots, general necrosis and ring spots are the most common symptoms of infection by INSV.
Perennials such as Campanula, Delphinium, Gaillardia, Leucanthemum and Monarda (bee balm) and buttercup are susceptible to INSV. Symptoms of INSV on buttercup include distortion, necrosis (browning) and spotting. On bee balm, the most commonly observed symptoms include necrosis and spotting. On other perennials, spotting of the leaves is a common INSV disease symptom. Mottling/mosaic, foliar distortion and chlorosis, and ring spots also are frequently observed. Because INSV is systemic, it may overwinter in perennials in the roots. Unsold perennials remaining in the greenhouse from year to year may come into contact with a wide variety of crops. Occurrence of thrips provides a dangerous link between infected perennials and healthy plants. The role of perennials as reservoirs may become more significant as the perennials industry grows.
To effectively manage INSV, growers should observe the following:
- Use yellow (or blue) sticky cards to monitor thrips populations. Count thrips and change cards weekly.
- Keep ornamental bedding and vegetable plants separated within the greenhouse.
- Do not mix bedding plants with cutting-propagated plants. The disease frequently enters the greenhouse via vegetatively propagated plant material.
- Do not hang baskets of cutting-propagated crops over seedlings. Young seedlings are highly susceptible.
- Eliminate weeds. They may harbor the virus.
- Immediately discard any plants with symptoms associated with INSV. Such a measure may prevent an epidemic in the greenhouse.
- Inspect incoming plants for signs of thrips feeding injury or disease symptoms associated with INSV.
- Submit suspect plants to a diagnostic clinic for testing, especially for crops where the losses have been greatest.
- Invest in propagative plants material that has been indexed for INSV.
Table 1. A partial list of bedding plants that may become infected with INSV.
Table 2. A partial list of potted plants and hanging baskets that may become infected with INSV.
||New Guinea Impatiens
Table 3. A partial list of foliage plants that may become infected with INSV.
Table 4. A partial list of perennials that may become infected with INSV.