Maximum Yield Australia/New Zealand May/June 2019 | Page 79

ematodes can either be a gardener’s
best friend or worst enemy. Plant
N parasitic
nematodes invade our gardens
and cause yellowing leaves, stunted
growth, and poor harvests. Beneficial
nematodes are powerful allies that feed
on harmful bacteria, fungi, insects, and
other nematodes that want our crops for
themselves. Beneficial nematodes also
break down organic matter and recycle
nutrients in the soil.
Nematodes are microscopic round
worms that can range in size from
0.05 centimetres up to several cm long.
They were some of the first organisms to
exist on the planet, having been around
for an estimated one billion years. They
live in water and soil and, depending
on the type, feed on bacteria, fungi, protozoans, other nematodes, insects, plants,
animals, and even humans. They are a vital part of the soil food web, serving as
predators, prey, and nutrient recyclers.
There are more than 15,000 known species of nematodes on the planet, with an
estimated 15 per cent of the species being parasitic towards plants. They are
so abundant that if you were to remove everything on Earth except nematodes,
we would still be able to see an outline of everything on Earth. In fact, just one
handful of soil can contain millions of them.
Harmful Nematodes
Plant parasitic nematodes are only about 0.05 cm long, with smooth,
unsegmented bodies. Most are long and slender, while some species are more
pear shaped. They have sharp, pointed mouths, called stylets, which puncture
cell walls and allow them to feed on tissues.
“Nematodes
ARE A VITAL PART OF
THE SOIL FOOD WEB, SERVING
AS PREDATORS, PREY, AND
NUTRIENT RECYCLERS.”
There are four classifications
of plant parasitic nematodes.
Migratory ectoparasites feed
on the outsides of the roots.
Sedentary ectoparasites
burrow their heads into the
roots to feed and stay there.
Migratory endoparasites tunnel
into the roots and then search
for another host when they
are done feeding. Sedentary
endoparasites burrow into
the roots and stay there
permanently to feed. Nematodes
will also eat parts of the plants
above ground at different times
in their life cycle.
They can cause some
serious harm, to the tune of
an estimated $77 billion in
damages to crops worldwide.
The most common plant
parasitic nematodes are root
knot nematodes. They get their
names from the damage they
cause to root systems. When
they puncture the root and move
in, they actually expand the
size of the root to make more
room for themselves and their
offspring. When you dig your
sick plants up at the end of the
season, you’ll find the roots
have knots in them.
Symptoms may include
yellow wilted leaves, signs of
infection, stunted growth, and
poor yield. Nematodes also
present as patches of poor
growth in an otherwise healthy
field, which may spread if
left untreated. If you suspect
nematodes are the cause of the
problem, you can gently lift
the plant out of the ground and
examine the roots. You may
see root rot, injured root tips,
small lesions and knots, or
excessive root branching.
The symptoms may be
mistaken for other issues
until you dig up the plant, and
sometimes there is no damage
to the plant at all. Healthy
plants can actually tolerate
small infestations without
suffering a loss in production.
Maximum Yield
77