In a 1999 SpongeBob SquarePants episode, a group of nematodes yell in unison, “Thirsty, thirsty, thirsty!” as they use straws to slurp up SpongeBob’s pineapple house until nothing is left. Nematodes can be a hassle, but they can also be beneficial.
Nematodes in agriculture and gardens
Nematodes are generally microscopic, unsegmented roundworms. They occur in soil, water, plants and animals. Plant-parasitic nematodes have a needle-like mouthpart called a stylet, which they use to puncture plant cells and feed on roots, stems, leaves or other tissues. Their feeding can cause galls or other swellings on roots, lesions or spots on leaves, stunting, wilting and sometimes plant death if the infestation is severe.
Farmers know the havoc nematodes can cause to crops, much like SpongeBob’s house. A 2013 Phytopathology review cited inflation-adjusted estimates of roughly $173 billion in annual crop losses worldwide and $13 billion in the United States, based on figures from a 1987 review by Sasser and Freckman. A USDA publication also notes that more than 100 species of plant-parasitic nematodes infect plants important to agriculture.
Some nematodes that damage crops include the soybean cyst nematode (Heterodera glycines) on soybeans; potato cyst nematodes (Globodera pallida and G. rostochiensis) on potatoes, tomatoes and eggplants; and the burrowing nematode (Radopholus similis) on bananas, citrus and ornamental plants. For farmers, key tactics for combating plant-parasitic nematodes include rotating to non-host crops and selecting varieties resistant to the nematode species present. Gardeners are cautioned against planting vegetables in the same location year after year for similar reasons. Resistant varieties are available for some crops, but not for every crop or nematode. Other options include certain French marigolds used as a rotation or mass planting and solarization of infested beds, although these approaches are usually more practical in gardens than in large fields.
Is it all bad?
While the aforementioned nematodes can be damaging to crops, there are some beneficial nematodes as well. For the last several years I’ve used beneficial nematodes on my properties, around the house and garden, for pest control and mitigation. These are typically insect-killing species (Heterorhabditis bacteriophora, Steinernema carpocapsae and Steinernema feltiae). Depending on the species, they can target soil-dwelling or soil-contacting stages of pests such as fleas, thrips, armyworms, fungus gnats, cutworms and some beetle larvae. Research also suggests that some beneficial nematodes or their bacteria can suppress plant-parasitic nematodes, but the results are species-specific and their effectiveness under field conditions remains uncertain.
Beneficial nematodes are also microscopic roundworms. They infect susceptible insects, usually larvae or pupae, in moist soil. They need moisture and protection from heat, direct sunlight and drying, so I apply them during mild, damp conditions or irrigate before and after application. Once they find a host, they enter it, release symbiotic bacteria and reproduce inside the dead insect. Since they are microscopic, their movement through soil is limited and varies by species and conditions. In one controlled microcosm study, 67–96% of the two species remained within 1.5 inches of the host cadaver, while only 0.4–1.4% reached 4.5 inches over 72 hours.
The Game of Life made me think that spreading them evenly might cause them to use up the available hosts and die out after the first few generations. I’ve therefore applied them in spots spread over larger areas. However, I haven’t found research showing that this makes them persist longer. In one turf study, nine patches controlled grubs about as well as a uniform application, while one large patch performed worse, and none of the patterns improved long-term persistence.
Entomopathogenic nematodes already occur naturally in many Oklahoma soils, although their distribution is patchy. Commercial products release large numbers so enough infective juveniles encounter the target pest, but OSU cautions that purchased strains may be non-native and could displace native entomopathogenic nematodes. A word of caution: their broader ecological effects have not been studied enough to say that large releases are harmless in every setting. Laboratory studies have found effects on ladybug and lacewing larvae, while field studies have generally reported smaller or temporary effects on non-target soil organisms. A 2026 laboratory study also found reduced honey bee survival after wet foliar exposure to S. carpocapsae, but that does not establish the same risk from ordinary soil applications or demonstrate effects on native pollinators or lightning bugs. It’s important to remember that anytime we artificially introduce a large number of organisms, even ones we perceive as beneficial, we could unknowingly be doing ecological harm.
Should I use beneficial nematodes?
They can help reduce certain pests in the garden and may help us get more out of our vegetable or ornamental crops. I recommend them to friends and family when the topic comes up, but I don’t recommend broad applications or using them in native areas.
Beneficial nematodes can be a tool in the gardener’s toolbox, but like any tool, they can be used incorrectly. In nature, nematodes we call beneficial and those we call pests are both part of the food web. Plant, insect and nematode populations all affect one another and help keep one another in check, although that balance is never perfectly stable. The more I read, the more I realized that “beneficial” describes what they do for us, not everything they do in the soil. We need to be cautious when altering the ecology to our benefit.