Friday, January 13, 2012

Sample of the Week: INSV on Cyclamen

INSV symptoms on cyclamen (Photo: M.J. Munster)
A potted cyclamen is a nice way to brighten up a cool windowsill in winter, but a cyclamen sample we received from a greenhouse this week did not look so pretty. The grower noted that the problem started with light-green mottling of the leaf edges. Eventually, these mottled areas turned brown and the buds died.
Necrotic spots on cyclamen, INSV symptoms (Photo: M.J. Munster)
Upon examining the plant, we observed mottling of the foliage, necrotic lesions on the leaves, and necrosis and decay of the crown. PDIC entomologist Dave Stephan also found Western flower thrips present in low numbers on the sample. We suspected INSV (Impatiens Nectrotic Spot Virus) and confirmed the diagnosis with an Agdia Immunostip test.
Positive Immunostrip Test (Photo: M.J. Munster)
INSV attacks a wide variety of hosts and is vectored by Western flower thrips (Frankliniella occidentalis), a tiny insect that feeds on leaf and flower buds, petals, and pollen. Thrips breed all year in the greenhouse and the virus can spread quickly when thrips are present. Symptoms of INSV infection vary widely from hosts to host. Typical symptoms in ornamental crops include mottling, yellowing, wilting, stem death, poor flowering, ringspots, and sunken lesions on the foliage.
Sunken necrotic lesion, INSV symptom (Photo: M.J. Munster)

Necrosis/decay of the crown (Photo: M.J. Munster)
Controlling INSV is difficult and the best management strategy is prevention. Both INSV and thrips have a very broad host range, so weed removal in and around greenhouses is an important part of prevention. Greenhouses vents should have screens to exclude thrips. Insecticides are only partially effective against thrips and virus transmission. Most systemic insecticides do not translocate well to flower parts where thrips feed, while insecticides that “kill on contact” may not reach thrips hiding deep in blossoms and buds.

Inspect and monitor all incoming plant material carefully to prevent introduction of INSV and thirps on stock plants. Any plants with suspicious symptoms should be isolated and sent to the PDIC to test for INSV infection. The virus can be spread by vegetative propagation. Since infected plants cannot be cured, and cannot be used for propagation, they should be destroyed.

For more information on thrips control, click here
For more information on INSV, click here