Virus-infected plant parts can show blisters, bumps or other distorted growth, like on this virus-infected pumpkin.
The time of year has arrived when people begin to worry about fending
off the common flu viruses. The feelings of malaise caused by viruses
can lead to some unproductive days in the garden. This is the time of
year when one should be busy clearing out diseased leaves and stems
to ensure healthy plants next year. Some might wonder if plants can
get the flu. Plants are susceptible to a variety of virus diseases,
although the general term "flu" is not used in the plant world.
Fortunately, the virus diseases that infect plants are unique to
plants. They don't infect people.
Interesting stories about plant viruses date back as far as the 15th
century. Virus-infected tulips created quite a stir known as
Tulipomania in Holland in the 1600s. Tulips at that time were
increasing in popularity. Some tulips showed streaks of color or
unusual line patterns that caught the eye of gardeners. These
colorful tulips, also referred to as Rembrandt tulips, became highly
desirable and sought after. It's even written that virus-infected
tulips were once used as a marriage dowry. People discovered that if
the ground bulbs of the multi-colored tulips were rubbed on plain
tulips, they could transfer the traits. What they didn't know at the
time was they were actually transmitting a virus disease that caused
the plants to be less vigorous. The colorful tulips that are
available today are not infected with a virus, but are developed
using genetic technologies.
Plants that are infected with virus do not always display colorful
eye-catching symptoms. Some plants simply grow poorly, a symptom
that can be attributed to a number of different factors, such as lack
of nutrients or drought stress. Patterns of scattered, interspersed
light and dark green on the leaves, a symptom called mosaic or
mottling, can indicate a possible virus infection. Ringspots,
concentric circles of yellow or white on leaves, also can be a
symptom of a virus infection. Virus-infected plant parts can show
blisters, bumps or other distorted growth. Finally, unusual line
patterns on leaves suggest a virus may have entered the plant.
The discovery of a virus-infected plant can be frustrating. Diseased
plants cannot be "cured," and the best course of action for gardeners
is typically to remove them to avoid spreading the problem. Viruses
also can infect important crops such as wheat, rice, soybeans and
citrus fruit. The result is often poor yields. There are hundreds of
different viruses known, many of which are specific to a certain type
Since plants don't sneeze, spewing virus-infected particles to their
companions around them, plant viruses require a helper, known as a
vector, to move from plant to plant. Vectors are most commonly
insects, such as aphids, leafhoppers, thrips, whiteflies and beetles
that spread viruses when they move from plant to plant during
feeding. Other vectors include mites, fungi and nematodes
(microscopic worms). Humans can also spread plant viruses. Pruning,
harvesting, grafting and other plant handling chores can potentially
transfer virus particles from plant to plant. Virus disease problems
can be spread when plants are transported from one location to
another, even from state to state. Because plants infected with
viruses do not always show recognizable symptoms, diseased plants may
pass through inspection procedures.
What do viruses look like? Because they are so small, even called
submicroscopic, it is impossible to see a virus with the naked eye.
They cannot be grown and examined in a laboratory test tube because
they can only reproduce in a living cell, such as a plant cell. The
presence of a virus can sometimes be diagnosed with a good degree of
confidence if characteristic symptoms are observed. In other cases,
specialized laboratory testing is needed to confirm the presence of a
Because there are no practical curative treatments for virus-infected
plants, management of these diseases is aimed at preventing viruses
from becoming established in your yard and garden. Always check for
the availability of plants that are resistant to important viruses.
Traditional breeding and genetic engineering are methods being used
to develop plants with resistance to disease problems.
So before planting, learn about common virus problems of the garden
and landscape plants you hope to grow, and plan to control vectors
known to transmit troublesome virus diseases. Finally, be a cautious
shopper and carefully inspect plants before installing them in your
landscape. Catching problems early by being alert to the appearance
of unexpected or unusual symptoms during the season will help avoid
losing valued plants to viruses and other pathogens.