Root Knot Nematodes
Question from Arline:
How can one get rid of nematodes? A friend of mine has a community garden and she has them in her plot…..any tips?
Answer from Pat:
There are many ways to get rid of root knot nematodes. I think I have now found the best way, but in order to answer this question fully I have to discuss all the ways.
Nematodes hate moist soil that’s full of humus. They thrive in dry sandy soil with low humus content. The benefit of sandy soil is that it has excellent drainage. On the negative side, it is “hungry soil” that uses up organic matter rapidly and as mentioned above, it is also prone to nematodes. Nonetheless, all types of soil are good if one manages each one properly. Largely this means amending one’s garden soil on a regular schedule, twice a year if growing vegetables or annual flowers, with organic matter and fertilizers as required. Mulch is also helpful in keeping soil moist and weed-free and gradually building up the organics in soil as it slowly rots on top of the ground.
For many years I grew veggies in the sandy soil on the terraces of my lower garden with great success by amending the soil with massive amounts of manure and compost and fertilizing adequately. I also watered my vegetable rows and even my wildflower bed, with a type of agricultural, burial-type, strip, drip system, called Hardy Bi-Wall. For vegetables other than tomatoes, the time clock was adjusted to irrigate for 10-minutes daily, which amounted to 2 to 3 inches of rainfall a week. This meant the ground beneath the rows was permanently moist but since it had excellent drainage, my vegetables thrived but that was a different era from today when current water restrictions make us extremely saving on irrigation.
In such sandy soil, even with this much irrigation there were dry pockets of soil beneath the paths between the rows. In order to be clear, I need to explain that I never irrigated tomatoes with a drip system since this would have resulted in their getting blossom end rot from uneven moisture in the soil. Instead, I always watered my tomatoes by soaking the row once a week deeply with the hose lying on the ground. Because tomatoes are deeper rooted than most other vegetable crops, this watering method produced even moisture in the soil for them. Their roots went deep to find water which was continually there, so they did not get blossom end rot. However, they did get nematodes due to the fact that some errant roots of the tomatoes stretched sideways beyond the area that was irrigated. Thus, during those years, I chose to grow nematode-resistant tomatoes (VFNT) only, such as Celebrity, Better Boy, Early Girl Improved and other varieties resistant to verticillium and fusarium wilts, nematodes, and tobacco mosaic virus, and in this manner I grew excellent tomatoes for many years. I should mention that during the 1980’s Early Blight and Late Blight on tomatoes had not yet reared their ugly heads.
As an aside, just think how many things have changed: When I first came to California in 1944, there were no tobacco bud worms gnawing round holes into our geraniums and wrecking the flowers. Try to imagine what heaven that was. During the forties and fifties many people grew solid geraniums instead of front lawns and they bloomed non-stop year round. Anyway, now that Early Blight and Late Blight are additional problems for tomatoes, I grow my tomatoes in a raised bed, and I have switched to growing heirloom tomatoes grafted onto resistant roots. Thus, no more Early Blight and Late Blight, but back once more to nematodes.
The years when I was growing my vegetables on the terraces began in the 1970’s and included the 1980’s when I was using my garden as a TV set for my news segment on the San Diego NBC television station’s 5:00 pm and later 6:00 p.m. newscast. (This EmmyAward-Winning show was called “Newscenter 39’s Resident Gardener” and my mission was to show gardeners what to do now in their gardens year-round, twice a week, 52 weeks a year.) During those – years to get rid of nematodes, I first fumigated the soil. After fumigation was outlawed, I tried out beneficial nematodes which kill destructive nematodes. However, I found that beneficial nematodes were unable to survive in my garden due to the fact that most areas of the garden dried out between waterings. Beneficial nematodes can only survive in moist climates or gardens where the ground is so heavily irrigated that it is continually moist. I also demonstrated soil solarization on my show, but for my purposes this method took too long. I needed all the space I had for my on-going year-round TV shows. Also, though soil-solarization worked like a dream it only lasted for the following season and after that the nematodes were back again.
I once demonstrated on TV how to plant a bed solidly with French marigolds (Tagetes patula) to rid the bed of nematodes. This system also works but you have to allow the marigolds to live for one whole season to rid the soil of nematodes. Then you pull them out and destroy them, and once again the treatment only lasts for the next season. During recent years, several varieties of marigold have been especially developed to kill nematodes. One of these is called Burpee ‘Nema-Gone’ marigold and there are others. My daughter Wendy has grown this amongst her vegetables and thought it helped even though she didn’t plant it solidly but just grew it here and there among the vegetables in her raised beds.
Today I grow my vegetables in a raised bed because it is easier for me and now in a time of greater water restrictions and more expensive water, I have discovered that the best way to get rid of nematodes is by digging shrimp shell meal into the soil. This works extremely well in raised beds or the ground. Shrimp shell meal contains very high amounts of chitin. Studies show that the chitin in the shrimp shell meal attracts large numbers of beneficial microbes that feed on chitin and multiply rapidly. When the chitin is gone they go onto feed on other organisms including root knot nematodes. Adding shrimp shell meal to soil occasionally seems to rid soil of root knot nematodes more quickly and effectively than soil solarization and my experience is that if you apply it in fall you will have no nematodes during that winter or the following summer. You can purchase 50 pound sacks of shrimp shell meal from Peaceful Valley Farm and Garden Supply. This amount goes a long way. Shrimp shell meal also contains nitrogen, phosphorus and calcium. Unfortunately, it is also alkaline. Our water supply is alkaline and our soil is already alkaline. We usually do not need to add calcium to our soil since there is plenty of it in the water. Thus we need to use shrimp shell meal wisely by applying it in fall before the rains so the alkalinity will be washed away. Managed this way the alkalinity doesn’t seem to affect the plants and in most cases the treatment lasts one year, so this means throughout the following summer of vegetable growing your plants should be protected from nematodes.
As a final note: Wormgold worm castings also help ward off nematodes and many insects since they contain more chitinase than most other dry bagged worm castings. Chitinase is an enzyme which destroys chitin. The exoskeletons of insects are made of chitin. Worm castings are not a fertilizer since they do not contain enough nitrogen or other nutrients to feed plants adequately. However, they are beneficial in other ways, most particularly in helping plants withstand pest problems.
Photo by UDel Carvel REC 
Thank you for the nematode info…my friend is grateful!!!
Your question gave me a chance to cover the waterfront on nematodes. I’m sure many people will be helped by these answers. Please tell you friend that she can always ask me a question on my blog at https://www.patwelsh.com. She does not have to ask you to ask me. I answer one question a day year round, which currently means every question is getting answered.
I watched your Nematode presentation and noticed your recommendation
of “Shrimp Shell Meal” from Peaceful Valley.
I have looked at the Peaceful Valley website and did not find Shrimp Shell;
possibly did you mean Oyster Shell Meal?
Evidently Peaceful Valley has lost its shrimp shell meal source. Now they are carrying crab meal instead. http://www.groworganic.com/crab-shell-meal-3-4-0-40-lb.html
Please be aware: No, I certainly did not mean to say ground oyster shell. Ground oyster shell is emphatically NOT the same as shrimp shell meal. Oyster shell is is made of calcium. As I know from having lived on our family’s Pennsylvania farm during the Second World War, chopped oyster shell is fed to chickens to make eggshells stronger. Ground oyster shell can be used to increase calcium in soil and in most cases we do not need that here since our imported water is high in calcium, which is alkaline. (Unfortunately crab shells and shrimp shell also add calcium to soil and thus are alkaline so it’s best to use them sparingly and only in fast draining soil or soil mix, such as in a raised bed or sandy garden soil which is where nematodes are worst.)
As I said in my lecture, shells of all insects and arachnids are made of chitin. Shrimp shell meal is largely made of chitin. For technical reasons (given below) when you add the ground up shells to soil it increases the chitinase content of soil. Chitinase is an enzyme that attacks chitin and this is why adding crab or shrimp shell meal to soil results in death to insects and also to nematodes.
Here is what Peaceful Valley says about ground crab shell:
“Slow-release organic fertilizer from dungeness crab, a by product of shellfish processing, is air-dried at low heat and crushed for a uniform easy-to-apply amendment. Studies have found that chitin provides a source of carbon and nitrogen for microbial growth in soil. Beneficial chitin-feeding microbes multiply in the soil and consume the chitin in the shell meal until it is gone. At that stage they move on to consume any other high chitin sources that might be in the soil.”
Nematodes are high in chitin. I think and hope that in my lecture I said “Crab shell meal also works!” but I know I go fast and give out a huge amount of information. Sometimes the listener cannot absorb everything Iwant to tell them. Unfortunately, I believe crab shells have a higher calcium content than shrimp shells but I am not sure. If you Google: “Shrimp Shell Meal” you can find other sources for shrimp shell meal. Even when used sparingly it has done a good job controlling nematodes in my daughter Wendy’s raised beds. Earthworm castings are another way to add chitinase to soil and earthworm castings are not highly alkaline. When using any of these products be sure not to breath in the dust.
Here is a link to a product called “Shrimp Meal Fertilizer” but if you read the information given you will see it is actually made of shrimp shells, not the whole shrimp. http://www.amazon.com/Down-Earth-Shrimp-Meal-Fertilizer/dp/B0057K74F2. it looks like a good product and is available in smaller quantities.
Hope this helps!
Many thanks for your response. Yes, I saw that Amazon has Shrimp meal… but I cannot get this
until the beginning of February. Does this meal need be in the ground during the growing season
or is it just an “instant fix?
Neither shrimp nor crabmeal are an instant fix, as few things are. First they need to be worked into the soil according to package directions, usually prior to planting. Then they must break down thus accelerating microbial action which in turn will lead to the demise of nematodes. Things you could add now to the top of the soil surrounding plants that would help to stop or reduce nematode populations include manure, compost, mulch and earthworm castings. The continuing rains will help to wash organic nutrients into the soil and increase microbial action beneath the surface. Do not use synthetic fertilizers, such as sulfate of ammonia and urea because these work in the opposite direction. They kill beneficial microbial action in soil but do not kill nematodes.
It is also thought by some soil scientists that tilling, plowing or turning over the ground with a plow, rototiller, garden fork or spade, as is customary in agriculture and vegetable gardening, is destructive to the buildup of fungus organisms that act naturally to control nematodes. All fungi contain chitin. Highly organic, moist, undisturbed soil is filled with strings or threads of protective fungi as part of its natural structure. For the last couple of years I have been trying this “no dig” system as an experiment in my raised bed where I grow vegetables. After the end of season, I pull out spent plants, clean-up the ground and then simply spread the new soil amendments: ie: Compost, organic fertilizer, manure and earthworm castings on top. After thorough irrigation, I plant straight down through this top layer. I got this idea from Steve Goto who uses this method for planting tomatoes since he is unable to rotate his crops. This is another way of thinking since it involves putting soil amendments on top of the soil instead of mixing them into the top foot or 8-inches as is customary. Steve’s advice indicates you could try putting Shrimp Meal on top of the soil and see what happens. If you do this please let me know results.
That said, my schedule for Southern CA gardening advocates planting summer vegetables beginning on March first. I think most gardeners are on too late a schedule. (Garden timing is one of the main points put forth by my books.) The point is, if you don’t plan to send for Shrimp Shell Meal until February and you begin planting in March you would be digging and preparing your garden for planting in late February. Thus your timing would be just right.
Dear Pat. We had gorgeous veggies growing in our raised beds this summer in north county San Diego and our tomatoes were producing like gang busters. We then began to have problems that have been uncharted territory for us. Some of the tomatoes had wilting, with yellowing leaves starting at the bottom, going up one side of the plant before spreading, apparently common with Fusarium wilt. Others had wilting with green leaves turning brown. There have also been some strange tiny white, tiny black and tiny winged green insects that we haven’t encountered before. At first we couldn’t be certain if the issues were because of insects or disease, as nothing seemed text book. We have fogged with neem/sal suds and later tried Captain Jack’s but it didn’t stop the insects from returning, or stop the wilting. As of 8/4, our store bought “Champion” is the only remaining tomato that is still mostly unaffected. The others were germinated from seed, half being heirlooms. We have pulled some plants that lost most of their foliage. A soil drench of 50/50 hydrogen peroxide/water has seemed to help the plants not as far gone. Adding another twist, we discovered signs of nematodes when we pulled our chocolate cherry. I hadn’t checked the roots on the others previously pulled, but have since noticed root knots on our green beans. It seems like solarization is a good idea to address multiple issues at once, so beds will be cleared & covered 9/1. I am buying some organic crab meal and I have already ordered the French marigolds you recommended for next spring. My question is whether we should mix in the crab meal and some compost prior to solarization, or wait until after we pull the plastic? Your advice would be greatly appreciated! Thank you so much!
I am sorry my partner on this blog send me your question so late. Sounds as if you did the right thing to use soil solarization. It makes no difference if you add the crabmeal first or later. Add compost later.
I am UC MG certified moderator for statewide FAQ page.
Question above has come up.
After considerable search, I cant find any UC, UCANR references on subject so I suspect it isn’t viable control.
I ran across article you did on Marigolds and chitin and wondered if you had anything to contribute.
Thank You in advance.
A few years ago I added crabshell meal to my raised bed in which I grow vegetables. Crabshell meal contains chitin. I never needed to use it again. No more nematodes. Earthworm castings also contain chitin and chitinase which destroy the exoskeletons of insects.