The more we learn about lawn and garden pests, the more we’ve come to love beneficial nematodes. Part of this comes from our study of various grub and worm pests that spend some of their lives in the soil. The other comes from the enthusiastic stories we’ve heard about the value of these microscopic pest destroyers.
The stories offer curious examples of the trial-and-error ways we come to learn about the gardening craft. And it’s also about the value of an Integrated Pest Management program, one that uses a variety of practices to deal with pests at all stages of development, not just when we start noticing damage to our lawns or our fruits and vegetables.
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Some of these stories start with yellowing turf or with scattered dead spots in a lawn. Good organic gardeners don’t wait for such problems to fester. These people had treated their lawns with insecticidal soaps. Some sprayed Bt-k, the naturally occurring soil bacteria. Their targets were white grubs, sod worms, mole crickets, webworms. These treatments are good for knocking down pests at a particular stage at a particular time. One story said that repeated BTK applications over a rainy week yielded results (BTK works best when applied in dry conditions) but then damage started to reappear. He’d only taken care of one stage of the pests. While he was destroying worms, pupae waited in the ground.
It wasn’t until the next spring that he applied beneficial nematodes. These wormy little microscopic parasites move through the earth until they find something to eat. They occur naturally in good rich soil that hasn’t been treated with chemical pesticides. Non-beneficial nematodes are vegetarians. They chew on roots and plant matter in the soil. Beneficial nematodes are carnivores. They don’t feed on plants. They feed on the pests that attack plants.
They can be an effective treatment, either concentrated on an infested area or broadcast in sufficient amounts over an entire lawn. The more pests they consume, the greater their numbers. They’ll consume any grubs of any kind they encounter. Knowing your target pest’s lifecycle can increase the effectiveness of nematode application. If you’re seeing Japanese beetles in your lawn, you know that other generations are there as well. Waiting three or four weeks and reapplying will help eliminate remaining pupae .
We’ve been told that we should wait until the soil begins to warm in the spring before broadcasting the critters. The thinking is that cold ground would not be encouraging. But it’s also suggested that late season is a good time to apply them to a lawn that’s had trouble, as we’ve learned. As long as the ground isn’t frozen or doesn’t freeze while the nematodes are seeking out prey, they’ll be fine. They actually prefer damp soil, so cold wet spring weather shouldn’t be a deterrence to use them. Fall applications might be best after cleanup and before applying compost if you so choose. As the lawn takes to its hibernation, the nematodes will be finishing off any pupae hiding underground, one by one.
In the meantime, those insect parasitic nematodes will also be going after other vermin who seek shelter underground: flea beetles, thrips, cucumber beetles, cutworms, even fleas. Beneficial nematodes don’t harm earthworms. They’re tunneling lubrication is too thick and slimy for the little nemi-worms to penetrate. But a thin-skinned pupae? (They’re also used extensively indoors and in greenhouses to control fungus gnats.)
Parasitic nematodes can be part of a good pest management program when used in an effective way. Any time you can eliminate two of a pests three stages, you’ve got them on the ropes.