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Photo by Timothy Schenck

The Dirt on Nematodes: A Gardener’s Unlikely Ally

By Erika Harvey | October 24, 2013

To the untrained – a category most of us fall into – gardens look pretty inert. However, beyond the beautiful blooms and verdant leaves of your common garden, a whole ecosystem of life is orbiting around the plants.A sparrow here, and a mockingbird there. Then there are the large beneficial bugs: worms aerating the soil, and spiders, lady beetles, and praying mantises munching on some of plants’ worst pests. Soil itself is packed with minerals, organic matter, and very importantly, a whole host of tiny and even microscopic organisms. A teaspoon of soil may contain up to a billion bacteria, many of which are beneficial to the garden ecosystem. All these critters together help support healthy soil and healthy plants, making plants more resistant to diseases and pests.

High Line Gardeners work hard to maintain a balanced garden ecosystem in the park’s planting beds, while keeping an eye on plant stresses, pests, and disease. This approach, called Integrated Pest Management (IPM), calls for close monitoring of the park’s plants, with a focus on preventative care and ecologically friendly interventions.

“The High Line’s horticulture staff are stewards of the park, but more than that, we see ourselves as stewards of the surrounding ecosystem as a whole,” says High Line Director of Horticulture Thomas Smarr. “It is our responsibility to use ecologically sound IPM practices to protect the environment and the community around us.”

IPM at the High Line has often involved biological pest control methods, meaning living organisms are used to combat pests. In the past, High Line Gardeners have released green lace wings to devore mites and aphids, and lady beetles to take on leaf hoppers. Compost and compost tea products are also useful in re-introducing healthy biology into the soil and onto the surfaces of plants to ensure a beautiful healthy garden. In contrast to chemical interventions, these types of biological methods leave the soil and ecosystem healthier and more resilient after their application.

This year, High Line Gardeners observed a sharp increase in Oriental beetles, Anomala orientalis, and Asiatic garden beetles, Maladera castanea, common New York garden pests. In the spring, pheromone traps were used to monitor and assess the beetle populations. (You can think of pheromones as species-specific scents that attract the beetles during their mating season.) Since a large number of adult beetles were caught in the traps, gardeners knew that there was a rough season ahead. In order to target the young Oriental beetle grubs at their most vulnerable time, High Line Gardener Orrin Sheehan spearheaded a program that involved applying nematodes when the grubs are young in mid-summer, before much damage could be done to the park’s perennials and grasses.

While what comes next might sound like a scene out of Alien, this particular species of nematodes, Heterorhabditis bacteriophora, only attacks grubs, and nothing else. Nematodes are microscopic worm-like organisms that reproduce through parasitism, in this case the parasitism of beetle larvae that feed on plants’ roots. Nematodes search out and colonize detrimental grubs, eventually killing them by eating them from the inside out. Fear not though, nematodes don’t present any danger to our gardeners during application, nor to plants or animals.

Nematode applications are just one of the many ways High Line Gardeners work to keep the park’s plants healthy throughout the year, while maintaining the highest standards for ecologically friendly gardening methods. Next time you’re at the High Line, think fondly of all the invisible creatures that are also lending a “hand” to help keep the park beautiful.