FEATURE
Plant-Parasitic Nematodes:
More Common on Golf Greens than you might Realize Introduction to Nematodes Nematodes are the most abundant animals on our planet. Scientists presently estimate that roughly 80% of all animals are nematodes. A shovel-full of garden soil may contain one million or more nematodes. Nematodes are found anywhere there is water, this includes oceans.
Nematodes have been recognized for five thousand or so years as parasites of man and other animals. Nematode parasites of humans cause some heinous diseases but they are far more common in impoverished nations. For this reason, nematodes fly under the radar screens of FRED WARNER most Americans. I have identified many NEMATOLOGIST biases that work against nematodes MICHIGAN STATE UNIVERSITY but a lack of publicity certainly is one. Although there may be some emerging problems with human parasitic nematodes in the U.S., only one disease caused by nematodes is a notifiable one according to the Centers for Disease Control (CDC) and that is trichinellosis (or more commonly, trichinosis). This is a nematode species found in swine (historically, it was more common in pigs than it is today) and many sylvatic North American mammals. Transmission to humans is typically by the consumption of undercooked muscles of the infected hosts. Some tasty, rare bear meat anyone? I’ll pass. The soil is a great environment for nematodes. The soil contains nematodes of different trophic (feeding) groups, the most abundant are nematodes that feed on bacteria. Most people are unaware 8
Michigan Golf Course Superintendents Association
of the key role these bacterial-feeding nematodes play in nutrient cycling. But, that is a topic possibly for another article. Plant-parasitic nematodes are obligate pathogens of plants. This means they cause diseases of plants and must have living host tissue (usually roots) to feed on or within in order to grow and reproduce. Every species of plant described has at least one nematode parasite. Please don’t make the mistake of thinking the coolseason turfgrass species we grow are immune from plant-parasitic nematodes. These nematodes do very well on grass and the species of grasses we frequently use on our golf greens host about a dozen or so kinds (genera) of plant-parasitic nematodes. Plant-parasitic nematodes are easy to ignore for many reasons. They are all microscopic with the longest one measuring about 6 mm (0.25 inches) in length. For comparison purposes, a female human guinea worm, which is often rolled out of infected individuals on sticks, can measure up to 800 mm (31 inches). So, since the majority of all soil-inhabiting nematodes are microscopic, you cannot stare into the soil and tell me how many of these colorless worms are present unless you possess Superman’s vision. Let’s face it, we tend to pay more attention to things we can see (macroscopic bias). In addition, feeding by plant-parasitic nematodes typically does not result in the development of characteristic secondary (above ground) symptoms. If we combine these observations with the fact many turf managers have limited knowledge regarding nematodes, it is easy to
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