The “V” Word (Viruses)

Ailments Culture

by Ken Slump

Posted by Sys Admin 5 months ago.

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A Troubling Problem for Orchids Growers


THERE IS PROBABLY NO OTHER word that elicits more confusion and fear among experienced orchid growers than virus. 

There seems to be no lack of experts when it comes to dispensing the truth about orchid viruses and I, like most, have heard a considerable amount of information (often conflicting) on the subject. Here is some of it. I offer these statements not as fact or fiction, just as hearsay:

  • A virus-infected orchid plant that drips on another at watering time, either from a hanging basket or open shelf, can transmit virus to the plant below it.
  • An infected plant can transmit virus to another orchid plant if their leaves are in contact.
  • Slipper orchids are not affected by orchid viruses.
  • A cattleya-type orchid that fails to produce vigorous new growth when repotted at the proper time is likely virused.
  • Plant viruses do not survive long outside of their hosts and can only be transmitted to another plant through cuts or wounds.
  • A mericlone produced from a virused plant may be free of the virus.
  • Every plant of certain all-time favorite orchid clones carries virus.
  • Orchids with viruses usually have color breaks in their flowers or recognizable patterns on their leaves.
  • Virus infection in an orchid plant can be verified only by testing.
  • There is no cure for a plant with a virus.
  • Many, if not most, orchids carry virus and it takes a stressful event for it to negatively affect the plant.

Those first two statements are enough to strike fear into the heart of nearly any orchid grower. My first concern about virus in orchids resulted from hearing the first statement at a time when I was growing my collection on open wire shelves — a commonly suggested and illustrated technique in some of the orchid books of decades past. It caused me to put trays with plastic grids under the plants to catch excess water, but of course, it did not prevent every drop from reaching a plant below.

Few orchid hobbyists enjoy such an extravagance of space that none of their plants touch. Nevertheless, it makes sense for the prevention of any insect or disease problem to give your plants all the room around them that you possibly can. Any plants in your collection that are known or suspected to have any serious problem ought to be isolated from the healthy ones.

I am not sure if I believe that touching plants or those that drip water on another will infect, but there is no doubt that cuts or wounds allow virus to enter a plant. For that reason, pots, pot clips and stakes should not be reused. Pruning tools and knives should not be shared among plants either, unless they are sterilized between cuts. You will hear recommendations among growers for sterilization techniques that employ chemicals or flame. For me, they have proven both inconvenient and hard on tools.

I prefer to use single-edged razor blades when making any cuts on my orchid plants. That is true whether I am dividing a plant or removing old growths at repotting time, or whether I am simply removing a spent flower stem or faded leaf from a plant. This is an important habit to develop as one must keep in mind that a fingernail pinching off spent flower stems can spread virus as easily as can the blade of a knife or pruning shears.

Of course, extreme care must be used with the single-edged razor blades. Wear leather gloves for some protection if you are uncomfortable handling them. To save money, buy packages of 100 or more at hardware or home supply stores. With economy in mind, I have been known to use a single blade for trimming leaves or flower stems from two different plants, being careful to make the first cuts from one end of the blade, then turning it carefully in my hand before addressing the second plant with the opposite end of the blade. Perhaps even more important than using such blades safely is the need to dispose of them in a safe manner as well.

There is little doubt that orchid viruses manifest themselves with symptoms that are visible on the flowers or foliage of some of their hosts. Yet I am pretty confident in suggesting that not every orchid plant that harbors a virus is symptomatic. It is generally accepted that testing is the only reliable way to confirm if virus is present in a plant. Only the foolhardy would proclaim any particular plant infected without incorporating an adverb such as “likely” or “probably” into their statement.

However, if orchid viruses’ only manifestations were cosmetic, we might not be so concerned about them. Indeed, some plant viruses produce desirable results. The mosaic variegations in the foliage of flowering maple (Abutilon hybrids), is viral in origin. Camellia fanciers introduce virus to some of their plants to produce variegations in the flowers. But the viruses associated with orchids frequently result in reduced plant vigor and flowering, a situation that nobody wants.

Which brings me to my personal situation, a comparatively small orchid collection that has been modified considerably in recent years. At the time I moved my orchids from Colorado to Florida, I had amassed nearly 500 plants, not a huge number, but plenty for the comparatively small sunroom in the high-rise building where I lived. About 150 plants came to Florida with me five years ago. Here, they are grown outdoors under shade.

The difference between the rather controlled cool to intermediate environment of my Colorado sunroom to the great outdoors of South Florida is major. Even with careful selection of which plants to move I have had surprises. Orchids that thrive in South Florida, really thrive here, and it is foolish to bother with those that do not. There is little you can do when you leave most of the environmental controls to Mother Nature.

As my reduced collection has adjusted to life in Florida, some plants have made the transition better than others. I have seen some of them gradually decline while others flourish as never before. I have discovered spots and symptoms on plants and foliage with which I am unfamiliar. Many of these I am still trying to decipher. In some cases, I suspected that virus was the problem.

This was particularly true for some of my older plants and a few of those I had acquired from the established collections of friends and at plant raffles. Unfortunately, it seems to be that many older orchid collections are rife with virus. While I seldom saw the color break symptom appear on flowers, suspicious spots and patterns on foliage have occasionally appeared.

Another problem with an outdoor collection is that insects are difficult, if not impossible, to control. I think it is safe to say that viruses may be transmitted between plants by insects with piercing mouth parts, such as the thrip and leafhopper, and perhaps even by such critters as aphid, scale and mealybug.

Certainly any plant under stress, whether it be from climatic issues, insect infestation or viral infection is likely to decline in vigor and fail to flower well or properly. As some of my plants languished or declined in their new home, I disposed of them, whether I suspected virus or not. I decided against testing every plant for virus, as it seemed that the expense and time were not worth it. I have orchids growing on tree trunks, stumps and driftwood in the landscape that are not necessarily practical to test or dispose of, so the possibility of infection to one of my potted plants from them may be only one thrip away.

After a few years I have amassed a small collection of orchids that thrive in this climate. These days, I am cultivating fewer but larger specimens. Among them I have a few old favorites and award winners that have suspicious foliage patterns that I suspect may indicate virus, even though those plants continue to grow vigorously and flower well. I am under no delusions about the archival or conservation value of my comparatively tiny collection so I wonder if it matters. At worst, they would increase the possibility of infection to my other plants. But perhaps it is time for me to have them tested and potentially be forced to make those hard decisions. It is a reality that sooner or later every orchid grower is likely to face.
 

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