Beneficial nematodes depend on moisture, timing

KANSAS CITY, Mo. – Beneficial nematodes – microscopic roundworms that move through the soil in search of insect pests – can help control white grubs, fungus gnat larvae and certain soil-dwelling caterpillars.

Once a nematode finds a suitable host, it slips inside and releases bacteria that quickly stop the insect in its tracks, says University of Missouri Extension horticulturist Tamra Reall. Afterward, new generations of nematodes emerge to search for more hosts in the soil.

As with any biological control, success comes from pairing the right tool with the right place at the right time, Reall says. Moist soil is essential for nematodes because they rely on a thin film of water to move around. Temperature is also important. Each nematode species has its own “comfort zone,” and applying nematodes outside those conditions can lead to disappointment.

How you apply them matters, too, she says. Nematodes prefer cool, shady and moist conditions, so it’s best to water the soil before and after application and avoid bright, direct sunlight. In Missouri, they generally perform best in irrigated lawns, garden beds and greenhouses where soil moisture can be maintained. In drier areas, results can be hit or miss.

Nematodes aren’t a magic fix, but they can be effective biological control agents if you use them under the right conditions.

Reall’s tips for nematode success

• Don't apply nematodes to dry soil or at the wrong time of year.
• Don't expect immediate reductions in pest populations.
• Match the nematode species to your target pest.
• Apply when soil temperatures and moisture levels are in the nematodes’ comfort range. Water before and after application to maintain soil moisture.
• Focus on areas where you can maintain good soil moisture.

Photo

White grub larva killed by Heterorhabditis bacteriophora, a beneficial nematode, next to two healthy larvae. Photo by Whitney Cranshaw, Colorado State University, Bugwood.org. Shared under a Creative Commons attribution license (CC BY 3.0).

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