Edible Gardening Series: Question of the Week – nematodes
By Carol Wyatt-Evens and Sarah Bostick
Gardening in Florida can be incredibly rewarding and incredibly frustrating, at the same time. If you are new to the region, you soon learn that gardening in the Sunshine State can quickly become a full-time job. While our subtropical climate is perfect for growing an abundance of different vegetables, fruits, and herbs, it also can present some overwhelming challenges.
We can help!
UF/IFAS Extension Sarasota County agents and staff have created an online edible gardening resource center. The website features short videos from our 25-episode “Edible Gardening Series” webinars, along with blog posts and resources list for episodes. Get help on an array of topics that befuddle many gardeners.
Each blog post in the Question of the Week blog series is associated with a specific EGS episode, but they are written for everyone to enjoy!
This week’s Question of the Week:
Can you give some guidance on soil, nematodes, and natural enemies?
The world happening underneath our feet is an amazing one. We don’t often think of soil as an ecosystem, but it is in fact, the most biodiverse ecosystem on the planet. In fact, a single teaspoon of healthy soil contains more micro-organisms than there are people on Earth. Soil is home to millions of species of organisms.
There is also a staggering diversity of soil types around the world. According to the United States Department of Agriculture Natural Resources Conservation Service, there are 23,000 “soil series” in the United States alone. Soil series are determined by comparing the natural layers, color, texture, structure, chemistry and mineralogy of soil.
The soil recipe:
Despite the truly incredible diversity of soil types, there is one thing that all healthy soil around the world has in common: it is made of a predictable combination of air, water, mineral, and organic matter. If you hold a handful of soil in your hand, about a quarter of the volume of what is in your hand is air, about a quarter is water, a little bit less than half is mineral, and around five percent is organic matter.
Organic matter, simply put, is anything that is or once was alive. Organic matter is where those millions of species of organisms that call soil home actually live. In a natural system, such as a forest or prairie, soil organic matter is continually replenished as leaves fall from trees, herbivores eat grasses and deposit manure, animals die, dead trees slowly rot, and so on.
Relationship between Vegetable gardens and soil
Vegetable gardens do not replenish their own soil organic matter. Every time you harvest a vegetable from your garden, you are affectively removing organic matter from your soil. The only way to replenish that soil organic matter in a vegetable garden is to intentionally add it back into the system. Two of the easiest ways to add organic matter into the system is to add compost to your garden and to use mulch. The materials we commonly use for mulch – things like straw, wood chips, Spanish moss, shredded leaves, seaweed, un-treated grass clippings, etc – were all once alive!
How does this all connect in to managing nematodes in your garden? Nematodes have natural predators. The natural predators of nematodes make their home in soil organic matter. Just like we plant wildflowers to provide habitat for beneficial insects above ground, we can provide habitat for the beneficial insects and microbial life below ground by building and preserving organic matter.
Plant-parasitic nematodes and natural enemies
The benefits of organic matter do not stop at nurturing plants, it goes well beyond that! Depending on the soil type, plant community, and management system, one square yard of soil will house between 500 to 200,000 individual arthropods. What is even more amazing, their collective biomass is far less that that of protozoa and nematodes! So, it is no surprise that you have nematodes in your soil.
The abundance of arthropod life is mainly contained within the top three inches of soil. Those arthropods along the top of the soil are the larger species; active, and voracious consumers. Some even climb trees to feed on pest caterpillars. They seek refuge under vegetation, plants, wood, or rocks. Below the surface, within a two-inch vertical space, are the smaller arthropods. These organisms are usually 1/250 to 1/10 of an inch. Tiny. Organic matter and organic volume have direct effects on the abundance and diversity of the arthropod community in your soil.
Biological control of nematodes
Of the natural enemies found in the soil, soil predatory mites are voracious predators of parasitic nematodes and a great example of biological control. Since most nematodes live within the soil and not on top of it, their predators must also be able to live or at least move within the same environment. The predatory mite species, Pergamasus sp, is only 1/25 of an inch long which is about 1mm, allowing it to freely move throughout the soil. They are generalist predators which means they feed on many different organisms, but nematodes are one of their favorite foods!
Springtails, one of the most abundant and interesting of insects, feed mainly on decomposing plants, pollen, grains, and fungi. However, when crossing paths with a nematode, they do not pass up the opportunity to take in a tasty nematode meal.
Predatory free-living nematodes are yet another abundant soil dwelling organism that will prey on parasitic nematodes. Yes, it is a ‘nematode-eat-nematode’ world!
Microbial predators- bacteria and fungi, are our final mention. These microbials are predatory on nematodes, but due to their lack of mobility in the soil, they take more time to come in contact with the pest nematodes. However, they are a very important control mechanism of plant-parasitic nematodes.
Having a better understand of your soil and realizing it is ‘living material’ makes it easier to understand why it is so important to ‘feed your soil’ and to take care of it. A diverse and abundant arthropod community in the garden is something to strive for, to conserve, and to celebrate. Conserving your beneficial arthropod populations will ultimately support successful, long term control of pest organisms.
Factsheets and resources for gardening in Florida:
USDA Natural Resources Conservation Service – Soils:
The Edible Gardening Series and blog series is a partnership between the following UF/IFAS agents and Sarasota County staff:
- Sarah Bostick, Sustainable Agriculture Agent
- Carol Wyatt-Evens, Chemicals in the Environment Agent
- Mindy Hanak, Community & School Gardens Educator
- Kevin O’Horan, Communications Associate