Treating Root Knot Nematodes Naturally in Tropical Soils
It’s been 6 years since I started to garden in the tropics. Year one I was full of hope, loving my year round hot weather but I was beaten back by pests, rains, mold and even the sun itself. Who knew the sun could actually be too hot for plants, I sure didn’t. With things like the Yucatan season calendar figured out it became easier to plan and protect plants from the harshness of sun and rain, why then were the plants still looking sick. I corrected with compost, I changed watering hours yet time and time again my plants would stunt and have low yields.
It was time to learn more and I figured it had to be something with the soil. Did I have too much of a nutrient? Was the soil acidic? Was it too rocky or too compact? After my 1st year in my current space I finally had the answer, nematodes.
This has become my most ask question on Nik of Thyme, “how do you deal with nematodes?” I am finally ready to share my trial and error of what has worked for me.
What are nematodes?
Nematodes are endemic to all soils worldwide, and some are very helpful for plants. However some nematodes, like root knot nematodes can suck the life out of your plants leaving them small and sick looking. Nematodes are too small to see with your naked eye but all the bad ones cause damage that can’t be solved with sprays or outer pest prevention. As I always say your soil health is your number 1 priority.
The easiest way to tell if you have this pest is checking the root of your plants. Root knot nematodes leave warts and large growths on the roots of infected plants. They also cause leaf curling and yellowing or discoloration, and the plant height and yield being stunted is the biggest indicator.
Plants like tomatoes, okra, peppers, eggplants, squash, carrots, sweet potatoes and many more can be negatively impacted by nematodes.
The best method in gardening (and life) is prevention, if you live in the Yucatan you should proceed as if you have root knot nematodes and prevent them before you plant. The only wish I have about my garden is wishing I could go back to year 1 and treat for nematodes before I started planting.
What to do if you have root knot nematodes
The most important thing is to NOT compost infected plants, this will just move the nematodes around more.
You want to throw the sick plants away immediately, don’t even set them down in neighboring grass.
After you have removed all the infected plants, don’t move the soil to any other part of the garden but till it up so that the nematodes are exposed to the sun. (gasp, I know I just said till, but this is the only time I will suggest such measures.) This won’t kill all of them but it’s a start in reducing your population because the sun will help you.
Natural DIY treatments for root knot nematode infested soil:
- Hot boiling water.
You can use hot boiling water to treat new soil before you add it to the garden. This is done by soaking the entire soil, and I usually do it twice to make sure the water gets into all the soil. I highly recommend you do this before spreading out the dirt. You will have to compost/nutrient correct this soil.
- Sun Solarization.
If you’ve been following along you know I had to do this last year. If, like me, you have already spread out all your soil then you have no choice but to treat it in the beds. Solarization with clear plastic is the best and fastest method to rid your soil from pests, but it still takes up time and space. Read more.
- Neem and lemongrass tea soak.
Another great method is to frequently add neem and lemongrass tea to your soil, something like yearly or twice a year should do the trick. You will take cuttings from the neem tree and from lemongrass and soak it in a big tub of water for 2 days. Use this tea to soak your garden beds. If you have a lot of beds like me you are going to need a lot of neem cutting and rounds of tea. Luckily many of your neighbors likely have the fast growing neem tree and will often gladly give them to you. Just remember to ask nicely.
- Marigolds as companion plants and cover crops.
It is known that marigolds kick the bad nematodes out of your soil because of naturally producing chemicals from their roots. It can be time consuming and cost space in a small urban garden to grow marigolds as a cover crop, but if planted at the base of tomatoes and other susceptible plants as companions you can get the same protection.
Things to note.
If your soil freezes every winter your root knot nematodes will naturally die, this article is for tropical and subtropical areas where soil is always warm.
There are also a number of commercial products you can buy to reduce your nematode population. Some are useful to organic gardeners but be careful because many will kill all your soil bacteria including the good nematodes and compost microbes. Some I can suggest in good conscience are neem seed meal and beneficial nematodes, but I have not tried either before.