Frequently Asked Questions
1. Tell me how to recognize INSV on impatiens plugs - I've seen spots on impatiens for years that turned out to be no problem after a few weeks.
Impatiens develop spots from fungal, bacterial and cultural problems as well as from INSV. Symptoms vary in different temperatures, varieties and ages of plants. INSV symptoms will be distinctive sometimes but an ELISA test or other laboratory confirmation should be done.
2. After some virus problems last spring, we cleared the houses and left them empty for the summer. This fall we grew Poinsettias and they were beautiful. Now our annual seedlings are showing symptoms and the scout says it's INSV. Where could the virus have come from all the sudden?
Did clearing the houses include weed control? Weeds serve as hosts for INSV too. Poinsettias do not and therefore that crop did not show any problems. However, the annuals were probably infected by thrips that had fed on infected weeds and then moved over to the young annuals.
3. Our operation has had thrips for years. We monitor and spray to keep them pretty much under control - they're not usually a big deal. If you have some thrips do you automatically get the virus too?
No, the thrips would have to feed on infected plants to start spreading INSV in your operation. However, now that INSV is so widespread in the greenhouse industry it's wise to continually monitor incoming transplants, cuttings or other propagation material.
4. If plants test positive but look fine why shouldn't we keep them in the greenhouse? And, is it ok to sell plants with this virus?
Never keep plants that you know have INSV. Such plants are a source of virus that thrips will spread to other plants. By selling plants with INSV you are passing the problem on to your customer. In addition it's likely that even though the plants look pretty good now they won't for long.
5. Two months ago we found out that we had INSV in impatiens hanging baskets. We rogued plants and sprayed heavily for thrips. Other impatiens in cell packs look fine and we haven't seen more thrips. How could it be that now our cyclamen suddenly wilt and die from INSV?
The cyclamen were probably infected before the thrips populations were brought under control. INSV has different effects in different hosts. Cyclamen often don't show symptoms until late in the production cycle and they are about to flower, then it's often devastating wilt and collapse of the plants.
6. What should I spray for the virus?
Unfortunately there is no spray for the virus itself. The spray portion of managing INSV is aimed at controlling the thrips vector.
7. About 6 weeks ago, maybe more, we got in some plug trays and ever since we've seen INSV popping up in several of our houses. We really think that the supplier sent us bad plants, we thought they looked bad at the time. What can we do?
You may have received infected plants, but now too much time has passed to say for sure. In the future, inspect every lot of plugs before you put them into your greenhouses. Suspicious plants should be held in a separate area and tested. If when you receive plants they don't look good, that is the time to take action. Reject the plants or test for INSV immediately if virus is suspected.
8. I have a plant that shows virus symptoms in some shoots but the other shoots look normal. I sent a shoot with symptoms in for identification and it came back positive for impatiens necrotic spot tospovirus (INSV). The recommendation was to destroy the plant. It is an unusual plant, and I want to keep growing it. Is it OK to propagate from the normal looking parts?
No, it would not be wise to propagate from a plant that has tested positive for tospovirus. The virus can be present even in shoots that show no symptoms. The virus is not uniformly distributed in the infected plant. We choose leaves showing symptoms for testing because there is probably more virus present in these leaves. However, low levels could be present in healthy-looking leaves. One of the best ways to spread viruses is to propagate from infected but healthy looking plants.