basics of plant diseases
In my experience, many people who
grow plants, whether for food, pleasure
or profit, often see problems with their
plants showing poor growth, blemishes
on leaves, dead or dying branches, or
outright plant death. When that happens, the following questions come to
mind: “What is causing the problem?
Where did it come from? How do I get
rid of it? And, how can I prevent it from
happening again?” As a plant pathologist for many moons, I have asked these
questions privately for my own plants,
grown for food and landscape beauty,
and professionally for commercial nurseries and farmers. As gardeners, both
outdoors and indoors, I judge that most
of you have asked these questions, too.
In this series of articles, I will present
the basics of plant diseases in hopes
that you can better address any disease
problems that may crop up with your
plants. This first installment will focus
on how to determine whether the problem you observe is either an infectious
disease or a non-infectious problem
brought on by some growth factor in
your soil or growing environment.
Signs and Symptoms
When you suspect something is wrong
with the way your plants are growing,
the first step in diagnosing the problem
is to characterize the symptoms you see.
Symptoms may be localized, such as
leaf spots, or systemic, such as stunting
or off-color foliage. In my experience,
stunting can be a general response to a
weakened root system that is not functioning to capacity. Examination of the
root system may reveal that many of
the roots are brown and dead-looking
instead of white and robust. Thus, the
problem may be localized in the roots
but causing stunting of the aboveground part of the plant. Another
thing to consider is whether all the
plants exhibit the same symptoms or
only a few here and there.
If the latter is the case,
I usually try to determine what is different
between the sick and
the healthy plants.
Below: For an infectious
disease to occur, three
fundamental elements are
required: a susceptible
plant, a pathogen capable
of causing disease and a
favorable environment.
= infectious
disease
t
en
“When you suspect something
en
pa
th
nm
og
ro
vi
en
The Disease Triangle
For an infectious disease to occur,
three fundamental elements are
required: a susceptible plant, a pathogen capable of causing disease and a
favorable environment. If any of these
elements are missing, no infectious
disease occurs. On the other hand, if
no pathogenic agent is present, but the
plants exhibit symptoms such as poor
growth or yellow or necrotic leaves,
and those symptoms occur on most
of the plants, then a non-infectious disease is likely.
Above: Root rot on a juniper
plant that diminishes
root function, causing
discoloration of the aboveground plant by limiting
water and nutrient uptake.
host
is wrong with the way
your plants are growing, the first step in diagnosing the
problem is to characterize the symptoms you see.”
112
Maximum Yield USA | February 2014