Managing Nematodes in your Greenhouse (Tips for the Tropics)

A previous client approached me in August 2014 on how to address the problem of nematodes that found their way into the greenhouse that I designed for them. Below are my recommendations.

The problem in this greenhouse (used to grow tomatoes that are safe from fruit flies) is that ants as well as mealybugs have taken up residence in the growing medium for the tomatoes. I suggest that the first step be pulling all of the plants out of the bags (we used growing bags to grow the tomato plants) in the greenhouse, leaving the bags in place. Also leaving the 10 healthiest plants there so that any remaining ants that escape out of the diatomaceous earth and carry any mealybugs with them will take them to the remaining plants. Next I suggest drying the bags out (minus the 10 remaining planted bags) for a period of six weeks along with adding diatomaceous earth to each bag. This will eliminate the ants and the mealybug in a dry diatomaceous earth living environment with no plants around them.


Nodules that nematodes cause on the roots of plants – not to be confused with rhizobia (See picture below).

The nematode, when set in hot dry conditions without plant life, will perish because it has only a 30 day cycle.

So in a 5-6 week time period keeping the bags completely dry with the diatomaceous earth (to get rid of the ant and the mealy bug) this will cause the demise of the nematodes.

After we have gone through a six week period with diatomaceous earth, no living plants in the bags, and hot dry environment, this will lead to the demise of the nematodes. Just after we’ve gone through this process then we add worm castings, humic acid, along with very fresh compost. The compost will also have sat with no plants growing in it for at least 30 to 40 days (using the Solarization process outlined below). Next we’re going to plant beans treated with rhizobia in the bags let them go through a cycle and only after that cycle will we be able to replant tomatoes.


Rhizobia (Beneficial nitrogen fixing bacteria) looks very similar to nematode nodules but are usually found on legumes. There job is to pull Nitrogen from the atmosphere and fix it into the soil making it available for plants.


Gliricidia leaves have the compounds present to deter nematodes, though the nematicidal marigold flowers (that are already present on property) are even more effective.


Solarization is another very effective method used in large farm areas to get rid of nematodes.

1. Spread the remaining medium in the pile outside the greenhouse out on a large black tarp, then cover with clear plastic for 30 days in full sunlight.

*The medium cannot be thicker than 4 inches high and the top clear tarp must be bigger than the black tarp. This can be done in smaller batches of 10×10.

**You can do this in a field where you want a large amount of weed suppression because the same 30 days should kill whats under the tarp as well.


2. Although this will still cause ants to inhabit this dry medium – which they love the very best. So the next step before you can put it in bags is to add diatomaceous earth to the dry soil in that last week or two. Mix it in while its dry which should help balance pH and add calcium.

3. When you are done with that, before adding the medium to the bags, thoroughly soak it. Then you are ready to fill additional bags in the greenhouse with this medium.

That will solve the problem of the bags in the greenhouse as well as the additional medium that’s outside the greenhouse.

Leave a Reply

Your email address will not be published. Required fields are marked *