Impatiens necrotic spot virus (INSV) has been around for 20 years. At one time there was a lot of discussion about this virus and growers were familiar with the hallmark symptoms it caused. With the discovery and identification of new viruses and blights, it’s easy to forget about familiar problems like INSV.

It is not hard to find INSV-infected plants at all stages of production. Too many diseased plants are making their way to retail, and it is unlikely that infected plants will perform very well the landscape.

Since INSV is a virus, no treatments can be applied to save an infected plant. The virus is transmitted by thrips and can infect hundreds of plants.

Ring spots are among the best-known symptoms caused by INSV and often occur on cyclamen, impatiens, cineraria, gloxinia and begonia. Ring spots may not occur on all plants infected with INSV. Less obvious symptoms, such as mottling, mosaic, poor growth and leaf browning, may go unnoticed or be blamed on other problems.

Infected plants showing only mild symptoms may escape detection and serve as a reservoir of virus for other plants. When infection by INSV results in no or only mild symptoms, the diseased plants may escape detection but can cause problems on plants that are more sensitive to the disease.

Crops susceptible to INSV

Bedding plants. INSV infects bedding plants, with impatiens and begonias being especially at risk. The most common symptom of INSV infection on impatiens is dark-purple ring spots on the leaves. Look for dark streaks on the stems or leaves, yellowing foliage and thin, straplike leaves.

When begonias are infected with INSV, the leaves look mottled with patchy, irregular brown and dead (necrotic) areas.

INSV on other bedding plants may cause spots, patchy and irregular brown areas, mottling/mosaic and ring spots. Plant yellowing, distortion and stunted growth are not always common on infected plants.

Crops infected: Ageratum, coleus, geranium, basil, dahlia, impatiens, petunia, begonia, dusty Miller, salvia, browallia, marigold, calendula, forget-me-not, morning glory, verbena, celosia, everlasting flower, nasturtium, zinnia.

Vegetables. Greenhouse-grown vegetable transplants such as peppers, lettuce and tomatoes may become infected with INSV. If so, expect large losses in yield and quality.

Crops infected: Pepper, lettuce, eggplant, tomato.

Potted plants/hanging baskets. INSV has caused devastating plant death in cyclamen, cineraria, New Guinea impatiens and gloxinia. On cyclamen, the most distinctive symptom of INSV is a thumbprintlike yellow ring spot on leaves. Flower petioles may also be distorted with brown streaks.

Symptoms on cineraria include faint ring spots or blotches on the leaves that gradually darken. Black streaks may occur on petioles. 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 symptoms or may dieback and collapse as a result of a black stem canker. Stunting, dark leaf spots or distortion of the foliage may also occur on INSV-infected New Guinea impatiens.

On other plants, INSV causes generalized browning and necrosis. Other symptoms are ring spots and chlorotic/necrotic spots. Less common symptoms are mottling/mosaic, distortion, yellowing and stunted plant growth.

Many plants propagated by vegetative cuttings (verbena for example) may carry the virus. Visual symptoms alone may not be adequate to detect INSV in propagation material.

Crops infected: African violet, Columnea, gerbera, primula, azalea, cyclamen, gloxinia, streptocarpus, calceolaria, exacum, hydrangea, Thanksgiving cactus, chrysanthemum, gardenia, New Guinea impatiens, verbena, cineraria, geranium, kalanchoe.

Foliage. Foliage plants are also susceptible to INSV.

Crops infected: Bird’s-nest fern, Nephthytis, silver evergreen, zebra plant, dracaena, Pedilanthus, spiderwort, ivy, peperomia, Swedish ivy, lipstick vine, piggyback plant, wax plant.

Herbaceous perennials. When ranunculus is infected with INSV, expect to find distorted growth, brown blighting and spotting. On monarda, the most common symptoms are browning of the foliage and spotting.

On other perennials infected with INSV, spotting of the leaves is common. Mottling/mosaic, foliar distortion and yellowing, and ring spots also occur frequently.

Because INSV is inside of the plant (systemic) it may overwinter in surviving perennials. Unsold perennials that remain in the greenhouse from year to year may come into contact with a variety of crops.

Crops infected: Aster, columbine, goldenrod, poppy, aubrietta, coreopsis, lobelia, stonecrop, barberry, dahlia, lupine, tiger lily, bee balm, daisy, obedient plant, veronica, bishop’s weed, delphinium, peony, wormwood, brachycome, evening primrose, phlox, campanula, gaillardia, polemonium. 

Tips to preventing INSV

1. Install yellow (or blue) sticky cards to monitor thrips populations. Count thrips and change cards weekly.

2. Keep bedding and vegetable plants separated in greenhouses.

3. Do not mix bedding plants with cutting-propagated plants. INSV frequently enters the greenhouse on vegetatively propagated plant material.

4. Do not hang baskets of cutting-propagated crops over seedlings.

5. Eliminate weeds that may harbor the virus.

6. Immediately discard any plants with symptoms associated with INSV. This may prevent an epidemic in the greenhouse.

7. Inspect incoming plants for signs of thrips feeding injury or disease symptoms.

8. Submit suspect plants to a diagnostic clinic for testing, especially for crops where the losses have been greatest.

9. Invest in propagative plant materials that have been indexed for INSV.

 

- Mary Hausbeck

TrackBack URI for this entry

Comments (0)

Subscribe to this comment's feed