A
s any doctor will tell you, the symptoms of one disease can look a lot like
another. A patient complaining of headaches could be suffering from stress at
work, poor eyesight, migraines, or a brain tumor. An aching knee can be caused by
overdoing it at the gym, tendonitis, arthritis, or brittle bone disease. It’s the same
when you’re trying to figure out what’s wrong with your plants. Yellowing leaves can
be a normal sign of aging or something more sinister like iron deficiency.
Without knowing what’s wrong, you won’t know what to do to put it right. Worse
yet, you might administer the wrong medicine entirely. To make the right diagnosis,
growers need to dig a little deeper, ask the right questions, and weigh all sorts of
clues. It’s a sleuthing exercise Columbo would be proud of.
Making the Right Diagnosis
“WITHOUT KNOWING
Diseases can be fungal, bacterial, or
WHAT’S WRONG, YOU
viral, and they can affect leaves, stems,
or roots. Pests attack all parts of a plant,
WON’T KNOW WHAT TO
eating away tissue or tunnelling holes
DO TO PUT IT RIGHT.“
that then develop secondary fungal
infections. Then, there are cultural
problems, the plant equivalent of malnutrition or heatstroke. These physiological
ailments caused by less-than-ideal growing conditions.
Regular patrols of your plants allow you to spot problems quickly, so spend a few
minutes every day just assessing what shape your plants are in. That way you’ll
notice every hole, puckered shoot tip, or browning leaf the moment it appears, and
you can swing into action before a pathogen takes hold. Even the slightest delay can
dramatically worsen the problem you’re dealing with; aphids, for example, repro-
duce so fast they quintuple their numbers every 24 hours, while blight can destroy a
previously healthy tomato crop in as little as 10 days.
Deciding which you’re dealing with is a matter of detective work. Arm yourself with
a good reference book on pests and diseases before you start so you have all the
information you need at your fingertips. The American Horticultural Society’s Pests
and Diseases is among the best. It’s a complete guide to every kind of plant ailment
with advice on prevention and treatment, as well as identification.
Be methodical in your inspections and try to keep an open mind. It may not be the
obvious sign that tells you what the problem is. It could be something much more
minor and difficult to spot, so look closely. Turn the leaves up and look at the under-
sides and inspect tender new growth like shoot tips where pests like to gather. Take
note of cultural conditions such as weather and when the plants were last watered.
Also remember many pests and diseases stick to just one family of plants. For
example, stunted growth in brassicas like cabbage and cauliflower could be caused
by clubroot, a nasty fungal disease that only attacks this group of plants. However, if
your cucumbers are also stunted, the cause is more likely to be a mosaic virus.
Gradually, you narrow down the field to just a few possibilities and, eventually, a
firm diagnosis. Then, treatment can begin.
Prevention is Better Than Curing
They say an ounce of prevention is better than a pound of cure, and that is so true with
plants. By the time you’ve spotted signs of a pathogen, some damage is already done.
So, grow disease-resistant varieties where you can, and pay attention to hygiene.
Take the few seconds to disinfect pruning shears between plants and spend half a day
cleaning the greenhouse properly at the end of the season to evict overwintering pests;
these small tasks make all the difference in keeping your plants healthy.
Just as important is growing your plants well. Keep them growing as vigorously as
you can by feeding and mulching regularly and providing just the right amount of
water, light, and humidity, and they’ll shrug off pest and disease attacks with ease.
Maximum Yield
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