The hidden enemy: Parasitic nematodes
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EmailEditor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Often
the things we fear the most are things we don’t understand or can’t see.
Does this include parasitic nematodes? Sure, parasitic worms sound
quite frightening as we usually don’t see them, only the symptoms of the
diseases they cause. In fact, nematodes can cause very serious diseases
of both animals and plants. The World Health Organization would list at
least a couple of species of nematodes among the 10 most important
pathogens of humans, worldwide. If you’ve ever seen a photograph of a
person infected with Wuchereria bancrofti, the causal agent of
elephantiasis (a serious disease resulting in grotesque swellings of
arms, legs and other body parts), you’d have a very good understanding
of the insidious nature of nematode infestations.
Well, what does this have to do with the production of vegetables in
Michigan? All species of vegetables have at least one nematode parasite
and some of these pathogens can cause serious yield losses. We often
refer to plant-parasitic nematodes as “the hidden enemy” because they
are microscopic worms and since they can’t be seen with the naked eye,
their presence often goes undetected. The only way to know for sure if a
field is infested with plant-pathogenic nematodes is to collect samples
of soil or plant tissue and submit those samples to a nematode
diagnostic lab for analyses. Fields going into vegetable production
should always be sampled for nematodes, preferably in the fall, the year
before vegetables are grown. Management strategies and tactics can be
planned or implemented at that time.
Some vegetables are planted early in the spring, so in these cases, it
is too late to sample fields for nematodes and implement control tactics
prior to planting this year (this is called problem avoidance.)
However, producers of vegetables should scout fields early in the year
for nematode damage. Nematodes will feed on plants very quickly after
roots are formed, so symptoms may appear as soon as a week or two after
plant emergence or transplanting. Feeding by northern root-knot
nematodes, Meloidogyne hapla, will result in the production of
small swellings on roots called galls. However, feeding by other
nematodes will not result in characteristic symptoms. Circular or
elliptical areas of stunted, yellow or dead plants are often the result
of parasitism by plant-parasitic nematodes. Growers should note these
areas and submit samples to MSU Diagnostic Services for confirmation of nematode problem diagnosis.
Unfortunately, if nematode problems are detected early this growing
season, growers can do very little to alleviate the symptoms they
observe. However, once fields are infested with plant-parasitic
nematodes, they will remain infested indefinitely. Therefore, records of
nematode infestations should be kept to minimize the risk to future
plantings.
It’s critical to remember, the only way to positively diagnose a
nematode problem is to submit a sample to a nematode lab for analysis.
If this is done routinely, unexpected crop losses of undetermined causes
can be minimized. Reduce the fear, let the enemy reveal itself.
Nematodes may not be so scary after all.
