Natural pest control: Nematodes

nematodesThe nematodes that you get at garden centres are used to kill insects, like white grubs, in your lawn. These are microscopic worms that attack and kill insects by entering their bodies and releasing bacteria, which kill the hosts in several days. They then feed on the body and reproduce inside of it. There are two kinds of nematodes in the package that you get from the garden centre: steinernema and heterorhabditis. Steinernema is an “ambush” nematode and waits in one spot for suitable insects to move close to it. They like a soil temperature of a minimum of 15° C.
Heterorhabditis nematodes are “cruiser” killers that go in search of insects and are really effective against sedentary white grubs. They like a soil temperature of 18 – 20° C.

Handling and application of nematodes

  • Find nematodes at a garden centre. They will be refrigerated, packaged in a bag which contains a sponge to keep them moist. 
  • Open the bag and take a whiff. A bad smell means that they’re decaying and no good. 
  • Take them directly home and put them in your fridge. 
  • Remove thick thatch from your lawn and ensure that high nitrogen fertilizer, herbicide or fungicide has not been applied recently. 
  • Ensure the soil is moist, not wet. 
  • Open the bag and put the sponge in water. Don’t let the sponge sit in water for more than 2 hours or you will drown the nematodes. 
  • Apply to the lawn using a hose end sprayer, watering can or small-pressure sprayer. Make sure you don’t have a small-holed screen on your hose, as the nematodes will be filtered out. Tip: if using a hose end sprayer add a food dye to the container so you know when the nematode solution is gone. 
  • Apply nematodes in the morning, at dusk or on an overcast day as they will be damaged if exposed to UV rays. Increase the rate of application of nematodes if you are trying to combat white grubs and your box of nematodes contains steinernema nematodes. This type of nematodes is ineffective in killing white grubs. 
  • Once applied, wash the nematodes down into the grass layer with a hose. 
  • Nematodes can take 2-3 days to kill the larvae; keep your soil moist.

When to apply nematodes

There are two times of year where nematodes are most effective, one being more successful than the other.

  1. The first is in the spring (April) when larvae are large in size and close to the surface. This is when a majority of lawn damage occurs, primarily due to the size of grubs.
  2. The second and more successful application time is in mid-August. This time of year, newly laid eggs hatch into tiny larvae that are very close to the surface. Because of their size, it takes far few nematodes to kill a larger amount of grubs. With seasonal temperature fluctuations, this time may vary from mid-Aug into the first week of September. Come October and November, grubs descend into the ground to prepare for winter and nematodes become less effective.

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