Nematodes are unsegmented roundworms, different from earthworms and other familiar worms that are segmented (annelids) or in some cases flattened and slimy (flatworms).

Nematodes that live in the soil are very small and most of them can only be seen using a microscope. A typical sod farm has many kinds of nematodes, most of which are beneficial as they feed on bacteria, fungi, or other microscopic organisms. There are also nematodes that can be used as biological weapons to use against other turf pests. However, one group of nematodes that are significant pests for sod farmers are the plant-parasitic nematodes that feed on plants.

Plant-parasitic nematodes have a stylet or mouth-spear that is styled much like a hypodermic needle. These pests use the stylet to inject digestive juices into plant cells. Plant-parasitic nematodes all feed on roots, however, some feed by sticking their stylet into the root (ectoparasitic nematodes) while others use the stylet to create a hole and go inside the root (endoparasitic nematodes).

Plant-parasitic nematodes damage the root system of whatever they feed on. Because of the damage caused by these nematodes, the affected plant’s ability to gather water and nutrients from the soil is restricted. Roots that have been damaged by plant-nematodes may be exceptionally short and have a dark appearance or will be rotten. Many times the roots will look as though they have been cut off approximately one inch below the soil surface. Root galls or knots that are typically associated with nematode damage to most crops are not present on grasses.

Symptoms that may indicate high population densities of nematodes include yellowing, wilting, browning, or thinning out of grass. Extreme nematode stress will kill grass. Nematode damage causes the grass to thin and as the grass thins weeds begin to fill in the vacated areas. The damaged areas may enlarge and weeds will invade the enlarged area. The weeds that creep into the thinned out areas include spurge, sedge, and Florida parsley.

The damage caused by nematodes can be identified by irregularly shaped patches in the sod. Also, in sod farms, nematode damage can be associated with slow re-growth following a sod harvest. The presence of plant-parasitic nematodes in significant quantities can also be symptomatic of sod that doesn’t “hold together,” making harvest difficult if not impossible. However, the presence of the previously described symptoms does not rule out other factors such as localized soil conditions, the existence of fungal diseases, or insects. The most damaging nematode of all the plant-parasitic types is the sting nematode. This nematode damages all types of turf grasses including Bahiagrass.

It is critical that a nematode assay be conducted by a professional nematode diagnostic lab to be certain that the problem you are experiencing is as a result of nematodes. You must have an accurate diagnosis of the problem to be sure you are not wasting time, effort, and expense on the wrong problem. Also, you will be unnecessarily making a pesticide application that can harm the environment and your sod.