The list of viruses identified to infect ornamental plants grows larger every month. These include previously identified viruses reported to infect a new host, or the identification of a new virus that has never been previously reported. As a professional plant pathologist and plant virologist, there are times I become overwhelmed with the amount of new reports of viruses and hosts published each month in the journals and trade magazines.
For a grower, I can imagine it's even worse. Just one more thing for them to worry about. One more thing that has the potential to destroy their crop and send them into economic turmoil. Sometimes I don't even tell growers about certain new viruses, because often the virus or the disease it is associated with won't have any significant economic effect. As a plant pathologist I understand that no virus is a good virus and a plant is sick and can not perform to its full potential if it is infected. However, as a Extension specialist working with growers on a daily basis I understand that it may be better to let sleeping dogs lie and there are situations where a plant can be virus-infected and for all intents and purposes be O.K.
I am also aware that many of the so called new viruses and new hosts are not new at all. Many of these new reports are the result of more advanced diagnostic technology. In other words, the virus has been there all of this time, we have just not been able to detect it until recently. More over many types of plants can be virus-infected and show few, if no symptoms of that infection.
Should a grower throw out thousands of plants because the plants were tested and they came back positive for geranium leaf twist virus ? Well the answer to that question is yes and no. There are viruses that if left unchecked can quickly destroy a crop. For example, impatiens necrotic spot virus (INSV) Fig.1 Fig. 2. This virus has a wide host range and can move from host to host rapidly if the thrips that vectors the virus is present. Even plants that don't show symptoms can be infected and can be a source for other infection in the greenhouse. I most cases INSV can render plants unsellabe within a short period of time. This is one virus that you don't want to mess with and a accurate and timely diagnosis is critical in managing this destructive disease.
On the other hand, a virus such as pelargonium flower-break virus (PelFBV) Fig. 3, which is a common virus found to be associated with geraniums is not cause for major alarm. PelFBV has been around for many, many years and most geraniums infected with this virus do not show symptoms. And even if they did show symptoms, the virus does not appear to cause any significant damage to the horticultural value of the plant. Should a grower throw out, prior to wholesale or retail plants infected with INSV? Yes, by all means. Should a grower throw out prior to wholesale or retail plants infected with PelFBV? Probably not.
Now, before I get myself into trouble, you must remember the USDA and your state department of agriculture has a whole list of viruses that, if identified in your plants, you have no other choice but to destroy the plants, and the point of this article is not to have you ignore those laws. The point of this article is to tell growers that not all viruses, if identified in your crop should warrant the destruction of your crop. We must put things into perspective when dealing with this situation. That's why it is highly important that if you suspect a virus problem, make sure you get the proper diagnosis before you do anything. After the proper diagnosis, your local university Extension specialist, county agent, or state agriculture official should be able to help you make a sound economic decision based on the results of your virus test. As in many things in life, it may even pay to get a second opinion, especially when it involves throwing your livelihood in to the trash. So, not all viruses are bad viruses, just the bad ones.
