Nematodes are microscopic organisms that get into the roots of your plants, and they form knots that prevent the uptake of nutrients through your plants. There are beneficial nematodes, and non-beneficial nematodes. The one’s we’re addressing here are “root knot nematodes”, and they are NOT beneficial. Some signs you may have nematodes can be: yellowing leaves, wilting leaves, and slow production that eventually leads to death of the plant. In the Summer time you may begin with a beautiful, lush garden that suddenly takes a turn for the worse. If you’ve been fertilizing on schedule, ensuring a healthy moisture level, and the garden is getting the recommended amount of sun but plants are slowing or stopping production mid-season, you should check the roots for nematodes.
Nematodes are present in all Florida soil. In most cases it’s not a matter of if, but when you’ll see nematodes. Our elevated garden beds do allow for a bit of an advantage because we control all soil inputs. That being said, there are many ways nematodes can find their way into the garden. They can travel through dirt blown into the garden during a storm. If your garden is surrounded by grass, dirt can be kicked up when mowing or doing lawn work. One way to prevent the spread is to make sure you always clean your tools by rinsing with water, then spray with alcohol in a spray bottle. If you’re working between landscaping and your garden, always clean tools between contact. If you have a garden confirmed with nematodes, spray your tools between working in that bed and others that are not yet affected. It is possible that some beds can have nematodes, and others do not.
Some plants are more susceptible to nematodes like tomatoes, peppers, cucumbers, squash, eggplant, and okra. If you suspect there may be nematodes in your garden, you can check each plant by gently digging around the roots. Typically the roots at the top of a plant are thinner, so to confirm try to get about an inch or two into the soil to the main roots to check for knots.
So, what can we do? One of the more practical methods is to solarize the gardens. This is the process of covering the gardens with plastic in order to create an oven like environment to bake out the nematodes. We do this in the last 6-8 weeks of the summer season when temperatures are high. The first step is to clear out all affected gardens of plants, and as many knotty roots as possible. Leaving those roots behind leaves nematodes behind. Then water in the garden thoroughly to make it muddy. We want the moisture to be maintained throughout the solarization process. Next, pull the soil away from the edges of the garden so you have about 3 inches of clearance. This allows space to tuck in your plastic sheet. We use 3 mm clear plastic so that it is strong enough not to tear, but also has good transparency for rays to pass through. Make sure the entire perimeter is secure as you lay the plastic around the garden by pushing the edges of the plastic down those three inches of space, then go underneath the sheet and push soil against the edges to secure them. Do this around the entire perimeter of the garden. Finally use fitted wooden slats to lay on top of the plastic as an added security measure.
The ultimate goal of solarizing is for the temperature of the soil to reach 120 degrees to cook the nematodes right out of the garden. This will also kill any weed seeds that have blown into the garden. This is why its so important to really soak the soil before hand because the moisture throughout the garden will help conduct heat in the lower levels of the soil, and not just the top few inches.
Keep in mind that when we solarize it not only kills the nematodes, but also all good bacteria as well. Over the course of the season, we work to really build that soil structure with worm castings, fertilizer, good microbes, and compost. The downside of solarizing is that is all undone. Keep that in mind when going into the Fall season. The soil structure will need to be rebuilt with a good fertilizing boost. When you do remove the plastic once solarization is complete, the top layer of soil can be a little gunky so we just scrape it off and discard the top layer of soil. If you need to raise the soil level this is the perfect opportunity to begin rebuilding the soil structure with organic soil, fertilizer, worm castings, azomite, and compost.
If you want to do more research into what kind of nematodes are affecting your garden, we have an incredible resource in the University of Florida Institute of Food and Agricultural Sciences lab. https://ifas.ufl.edu/ They have a nematode lab so you can more accurately assess what kind of nematodes you have for the best treatment options.
There is no guarantee that after solarizing your garden will be free and clear. Since our beds are made of wood and covered with a lining, there are many places the nematodes can hide out. The solarizing definitely helps to knock the population of nematodes in the garden down, but it will still take time and nematodes can come back. Once we get into the cooler Fall season, you may think you’re in the clear but the nematodes thrive in hot, wet environments. They often go dormant in the Fall just to return the next Summer.