Control pests the natural way
Nematodes are the biological superstars that keep those plant-wrecking nasties in check
Have you ever watched natural history programmes and marvelled at the beauty – and brutality – of nature? One minute you’re observing wildlife in its natural habitat, next it tries to avoid becoming dinner for a hungry predator.
A similar cycle is being played out in gardens, albeit on a microscopic scale. Pathogenic nematodes introduced to our plots relentlessly hunt down and dispatch specific pests, helping gardeners to control plant-wreckers without resorting to chemicals – a bonus for organic growers. Here, we look at how biological control nematodes can work wonders at keeping pest populations in check.
What are nematodes?
According to the RHS, there are more than 25,000 known species of nematodes, most of which are microscopic and occur naturally in soil or marine ecosystems. Certain species are highly regarded for their ability to kill troublesome pests such as slugs and grubs. Nematode specialist BASF, supplier of Nemasys and Nemaslug biological controls, explains that nematode means ‘thread-like’ in Greek, pointing out that these tiny multi-cellular worms with smooth, unsegmented, translucent bodies ‘are found in fresh water and saltwater, deep underground in mines, at the top of mountains and from the tropics to polar regions’. BASF claims there are ‘60 billion nematodes for every human on earth’ – and there are 7.8 billion humans on the planet!
How do they work – and are they safe?
Nematodes are effective predators that are said to pose no threat to humans or plants because they only attack specific pests. The process is a little gory (apologies if you’re having a cuppa and a biscuit while reading) but understanding their lifecycle helps to demonstrate how these tiny critters work. The microscopic worms enter a pest via its natural body openings and release bacteria, causing an infection that kills it. Nematodes will then feed on the decomposing pest and multiply, releasing a new generation which disperses to track down more prey, continuing the beneficial work. Once their host food source has been exhausted, meaning the pest is under control, the nematodes will die. They're often used to tackle vine weevil, slugs, leatherjackets, chafer grubs, caterpillars and codling moth.
What is the best way to apply nematodes in my garden?
Nematodes bought by mail order must be kept refrigerated once delivered (store packs out of harm’s reach in fridges, so they don’t accidentally get mistaken for food!). Observe the expiry date, because most will need to be used within four to six weeks. Also take note of the minimum soil temperature required for application, which commonly varies from 5-12C (41-43F), depending on the type of nematode. Each product has a specific season of application depending on the target pest. While Nemasys Biological Vine Weevil Killer and Nemaslug (a slug control) can be applied between March and October, for example, Nemasys Biological Leatherjacket Killer should be applied between August and October, so it targets newly-hatched larvae. Most nematodes are diluted in water, stirred vigorously and applied using a watering can with a coarse rose.
Do all nematodes have to be kept in a fridge?
In the past the answer was yes, but there’s now an exception to the rule. Neudorff, the German supplier of natural gardening products, has introduced three products that can be bought at UK garden centres and don't need to be kept chilled.
This has been achieved by placing the worms into a state called ‘cryptobiosis’, which prevents them moving or using oxygen but keeps them alive for up to six months. Neudorff’s VineWeevilFree and ChaferGrubFree nematodes also attack fungus gnat, cucumber beetle, gall midge and repel ant larvae, while Leatherjacket Free nematodes claim to also be effective against wireworm, caterpillars, strawberry root weevil, codling moth and leaf miner.
Nematodes come in soluble sachets, so they don’t have to be handled, and can be watered on using a special hose-compatible, pre-calibrated sprayer. They need moist soil at temperatures of between 10-30C (50-86F) to be effective, and are best applied in the evening on overcast or rainy days.