I’ve been planting the odd Marigold and Chrysanthemum for a while now. Not only do they have pretty foliage and have very nice flowers, but the Bunnies use them as natural flea control. (Mums have pyrethrins in them). Since I can’t catch the bunnies to give them a ‘flea bath’, at least I can let them do the medicating themselves…
At any rate, the question of “nematodes” came up on another thread. I’ve never had to deal with them here, but it looks like (especially in the South) they are a common issue.
Well, while knocking around looking at other flowering plants (poppies) I ran into the factoid that Marigolds can be used as a form of Nematode control. I already knew you could use Tobacco as a pesticide (both as a ‘trap crop’ for leaf miners, who lay their eggs on those big attractive leaves, only to have the nicotine assure they will never hatch; and as ‘tobacco tea’ spray) and that dried Chrysanthemum could be used as a dry powered insecticide. But along the way I ran into the point that Marigolds can be used for nematode control. Well, as at least one of the readers here is building raised beds due to nematodes, I thought that maybe having an alternate flower crop might be easier… and prettier too!
So here are some links along with some minor excerpts:
Root-knot Nematodes: Biocontrol with French Marigold
Root-knot nematodes (Meloidogyne spp.) can be effectively managed in home gardens without pesticides. One alternative to using nematicides is to intercrop and rotate vegetables with marigolds. Most cultivars of African marigold (Tagetes erecta) and French marigold (Tagetes patula) are effective in reducing the most common root-knot populations—Meloidogyne incognita and M. javanica (Table 1)
The roots of these attractive flowering plants contain chemicals that kill nematodes. As a method of biocontrol, growing marigolds is not only pleasing to the eye but economical and environmentally sound as well. One drawback, however, is that the benefits are not realized until the following year. Also, the treatment frequently needs to be repeated with marigolds and vegetables grown in alternate years.
Be careful when you buy marigolds to help control nematodes. Not all marigolds sold as bedding plants are effective against nematodes. Tagetes signata cv. Tangerine Gem, for example, will not control root knot.
To use marigolds to manage root-knot nematodes, follow these steps.
Collect a soil sample from the root zone of a living, but apparently unhealthy, plant. Include roots in the sample. Submit this sample to the Nematode Assay Section of the NCDA&CS Agronomic Division to verify that root knot is the problem. It is also a good idea to send a soil sample to the Soil Testing Section for lime and fertilizer recommendations.
At the end of the growing season, remove as many roots as possible from the soil by pulling, plowing or tilling. Doing so will reduce the number of safe places where nematodes can survive during the winter.
In winter, till the soil several times to expose nematodes to the sun and weather.
Apply lime according to soil test recommendations.
In spring, plant half of the garden with marigolds and half with root-knot-resistant vegetable cultivars. Plantings in blocks or strips are easy to manage (Figure 1). Strips may comprise one or several rows of vegetables. Contact your county Cooperative Extension agent for Plant Pathology Note 6, which lists nematode-resistant vegetable varieties. Table 2 indicates the amount of marigold seeds or plants needed based on area.
Use a marigold variety known to be Tagetes erecta or T. patula.
Space marigold plants, or thin seedlings, so they are 7 inches apart (Figure 2).
Fertilize according to soil test recommendations. Nutrient imbalances can make nematode problems worse.
Early in the growing season, cultivate between marigolds regularly to keep weeds under control.
Before the first frost, remove as many seed-bearing flower heads as possible. Then, you will have seed for next year’s marigold patches, and fewer volunteer marigolds will sprout among your vegetables.
In the fall before crop residue destruction, take another soil sample for nematode assay from the marigold area, if you want to monitor effectiveness.
Till the remaining marigolds into the soil.
The following spring, repeat the process with this exception: plant marigolds where you planted vegetables the previous year and vice versa.
If you know you have nematodes, looks to me like you can skip all the “assay” parts. Also, as I like Marigolds, I could easily see just having them be the “default” planted all around the borders all the time (to prevent migration in) and having them in all the interior ‘unplanted’ areas as well. Then just have them growing in any garden blocks not actively being “farmed” at the moment, and always alternated in from time to time. Seems like you could have a very colorful and productive garden “right quick”…
This guy has a different thesis (that the marigolds don’t kill the nematodes, just trap them). He does give a list of some of the crops that are sensitive to nematodes, so you know what to use with care. Personally, I’d go with the .edu guys, but here’s this guy’s take on things:
The truth about marigolds
Published: Saturday, May 03, 2008, 5:53 AM Updated: Sunday, May 04, 2008, 8:13 PM
By Dan Gill, Times-Picayune garden columnist
A good example is the marigold, frequently recommended as a companion plant for vegetables to prevent insect and nematode damage. As is often the case, a kernel of truth has been applied too broadly in spreading this advice.
There are no real benefits in repelling insects. In fact, marigolds have their own pest problems. Spider mites are particularly attracted to marigolds, and they are also a leading pest for tomatoes and other vegetables. Populations of spider mites can build up on marigolds and then move on to vegetable plants.
Planting marigolds near vegetables for nematode control, however, contains that kernel of truth: Marigolds can help control some of the most damaging nematodes that attack garden vegetables.
Parasitic nematodes (many other nematodes are harmless or even beneficial) are small, microscopic worms that attack the roots of many vegetables, reducing both yield and quality. Tomatoes are a favorite host, and most tomato cultivars we grow these days have been bred to be resistant to nematodes. Many gardens show the adverse effects of these pests by mid-summer.
The marigold is one of the few plants that produces substances detrimental to nematodes, according to Charles Overstreet, extension nematologist with the LSU AgCenter. He adds that asparagus, pangola grass, neem and castor beans also produce substances toxic to at least one or more kinds of nematodes.
Unlike these plants, which are natural nematicides, marigolds act as a trap crop. The nematodes enter the plants and are killed because they can’t set up successful feeding sites.
Although marigolds control several types of nematodes, their greatest effect seems to be on root-knot and lesion nematodes, Overstreet says. The Southern root-knot nematode is Louisiana’s biggest nematode pest.
Most marigolds, with the exception of the Signet types, appear to be effective against the Southern root-knot nematode. The French marigolds (Tagetes patula) are more effective than the African types (Tagetes erecta). You occasionally will find seed offered in catalogs for marigolds selected especially for nematode control.
How and when you plant the marigolds makes a difference in nematode control. Planting them simply as companion plants next to crops that are susceptible to root-knot nematodes doesn’t seem to work. The root-knot nematode can still develop on susceptible plants.
Instead, it’s best to plant marigolds as a cover crop in the rows or areas where you want to reduce the nematode problem. Early summer crops such as tomatoes, snap beans, cucumbers, squash, onions, garlic and strawberries are often pulled up in June or July, when they finish production. Marigolds can then be planted in their place.
Other techniques that will help reduce nematode problems include working generous amounts of organic matter into the soil (this encourages natural predators that attack nematodes), using nematode-resistant cultivars when available, solarization (covering the soil of an empty bed with clear plastic to heat the soil to a temperature that kills the nematodes) and using products for nematode control that contain chitin (the primary component of crawfish and shrimp shells).
So have yourself a mess of crawfish and shrimp scampi and put the ground up shells into the garden!
I’d be careful with that Castor Bean advice. Yeah, the ricin in them will kill just about any animal. But that’s the problem. A kid swallows a couple of beans and you can have a dead kid. Even the foliage is deadly.
Now planting Asparagus, that has potential!
These guys have a very extensive write up on nematodes, along with some great pictures. I note that they are less keen on the ‘turning over the soil’ idea:
The food-web’s stability is challenged by the yearly turning of the soil, which reduces the numbers of organisms that displace or prey on plant-parasitic nematodes, while bringing more nematodes to the surface from deeper soil. If the same host crop is planted year after year, plant-parasitic nematodes may increase to damaging levels. Root-feeding nematodes are very opportunistic, and are among the first organisms to invade after a disturbance. (Dropkin, 1980; Ingham, 1996)
Keeping these facts in mind, it is important to actively manage soil biology using minimum-tillage practices, compost, animal manures, green manures, cover crops, and crop rotations. These practices help promote the growth of beneficial organisms while suppressing plant parasites. Certain organisms that are associated with well-managed crop soils—e.g., Rhizobacteria and mycorrhizae—may induce systemic host resistance to nematodes and to some foliar diseases. (Barker and Koenning, 1998) For further information see the ATTRA publications Sustainable Management of Soil-borne Plant Diseases and Conservation Tillage.Soil amendments for nematode control
Some sources of organic matter known to be nematode-suppressive include oilcakes, sawdust, sugarcane bagasse, bone meal, horn meal, compost, and certain green manures.
Most nematode species can be significantly reduced by tilling in chitinous materials such as crushed shells of crustaceans (shrimp, crab, etc.). This is effective because several species of fungi that “feed” on chitin also attack chitin-containing nematode eggs and nematodes. Increasing the amount of chitin in the soil will also increase the population of these fungi. A shrimp-shell-based fertilizer called Eco Poly 21™ Micro shrimp fertilizer is available from Peaceful Valley Farm Supply. At 2002 catalog prices, it would cost between $87 and $216 to treat an acre with this product (the suggested application rate is 20 to 50 lbs. per acre). Clandosan™, a nematicide made of crab shells and agricultural-grade urea, can be used as a pre-plant treatment (it should not be used on plants because the amount of urea in it can “burn” or kill them). (Fiola and Lalancettle, 2000)
So, add a load of compost, make sure there is some fungus food and some mushroom / fungus active, put in some sawdust or animal meals… and eat more shrimp! Get friendly with your local seafood restaurant and collect those left over crab shells! And, in a blatant example of ‘selection bias’ I’ll take the ‘low till’ over the “shovel that garden twice a season” advice any day! ;-)
This is a particularly rich page for “ideas”. They have a whole section on “rotations” of which I can only quote a bit. The most interesting part to me was the use of Sorghum and Cruciferous vegetables as alternative nematode controls. Heck, I can make an entire vegetable garden out of the Cruciferous plants! (They use the new term Brassicas, that I usually avoid, as it makes me think of Brass Monkeys… yeah, it’s just a ‘how it is filed’ connection…but you have a very frost and cold hardy group of plants… with “brass” in the name… )
Even better is a rotation from a broadleaf to a grass. Asparagus, corn, onions, garlic, small grains, Cahaba white vetch, and Nova vetch are good rotation crops for reducing root-knot nematode populations. Crotalaria, velvet bean, and grasses like rye are usually resistant to root-knot nematodes. (Wang, et al., 2004; Yepsen, 1984; Peet, 1996) Rotations like these will not only help prevent nematode populations from reaching economic levels, they will also help control plant diseases and insect pests.
Allelochemicals are plant-produced compounds (other than food compounds) that affect the behavior of other organisms in the plant’s environment. For example, sudangrass (and sorghum) contain a chemical, dhurrin, that degrades into hydrogen cyanide, which is a powerful nematicide. (Luna, 1993; Forge, et al, 1995; Wider and Abawi, 2000) Some cover crops have exhibited nematode-suppressive characteristics equivalent to aldicarb, a synthetic chemical pesticide. (Grossman, 1990)
Farmers in Alabama have added sesame into rotation with cotton, peanuts, and soybeans. Nematode levels are reduced and yields significantly increased among those crops in fields previously planted in sesame. Sesame yields averaged 1500 lbs per acre, well above the world average of 500 to 600 lbs per acre. (Anon, 1997a) Research shows that sesame may be an effective rotation crop to control peanut root knot nematode (Meloidogyne arenaria) and southern root knot nematode (Meloidogyne incognita). Sesame rotation is not effective, however, for the Javanese root knot nematode (Meloidogyne javanica). (Starr and Black, 1995) Commercial nematode control products derived from sesame include Dragonfire™ (oil), Ontrol™ (seed meal)—both manufactured by Poulenger USA—and Nemastop™ (ground up sesame plant) from Natural Organic Products.
In South Texas, soybean varieties were shown as possible alternatives to grain sorghum in cotton cropping sequences. Eighteen soybean varieties of maturity group 5, 6, 7, and 8 were tested in Rotylenchulus reniformis-infested soil, either nonfumigated or fumigated with 1,3- dichloropropene. Reproductive rates of R. reniformis were compared in the first year. Both experiments were planted with cotton in the second year to measure the rotational effects of soybean on cotton yield compared with grain sorghum and fallow. The high-yielding soybean cultivars with potential to suppress reniform nematode were “HY574,” “Padre,” “DP7375RR,” and “NK83-30.” (Westphal and Scott, 2005)
A 2000-2002 Maryland study evaluated crop rotations and other cultural practices to manage southern root-knot nematodes and lesion nematodes. Researchers grew nematode-susceptible potatoes and cucumbers, and compared the effect of several summer rotations on nematode problems. A summer rotation of sorghum sudangrass (Sorghum bicolor x Sorghum arundinaceum var. sudanense) reduced the root knot nematode population as effectively as the control treatment (soyabean cultivar with no known root-knot resistance and one nematicide application). Poultry litter/tillage (Year 1) and fallow (Year 2) were equally effective in managing the lesion nematode population. To maintain the effect, the rotations had to be included annually. Either summer or early-autumn sampling dates were more effective than midspring to identify threshold levels of the pests. (Kratochvil et al., 2004)
So it looks like a ‘rotation’ with the odd ‘chicken shit then fallow’, with an occasional run through a nice Sorghum (the bicolor is great to look at, and you can make sugar syrup from some types) would also help. That point about the foliage breaking down in the soil to make cyanide is a nice touch too ;-)
Allelopathic cover crops
Some plants produce allelochemicals that function as nematode-antagonistic compounds, such as polythienyls, glucosinolates, cyanogenic glycosides, alkaloids, lipids, terpenoids, steroids, triterpenoids, and phenolics, among compounds from these plants—e.g., castor bean, chrysanthemum, partridge pea, velvetbean, sesame, jackbean, crotalaria, sorghum-sudan, indigo, tephrosia—are exuded during the growing season or released during green manure decomposition. Sunn hemp, a tropical legume, and sorghum-sudan, a prolific grass plant grown for its biomass, are popular nematode-suppressive cover crops that produce the allelochemicals known as monocrotaline and dhurrin, respectively. (Chitwood, 2002; Grossman, 1988; Hackney and Dickerson, 1975; Quarles, 1993; Wang et al., 2002; Williams and Williams, 1990a, 1990b, 1993)
Personally, I’d go with the sorghum or sesame…
Rape or mustard plantings in rotation with strawberries have checked the increase of some nematodes. (Brown and Morra, 1997)
Rapeseed and sudangrass green manures grown prior to potatoes at Prosser, Washington, provided between 72 and 86 percent control of the root-knot nematode in that crop. (Stark, 1995) In the same study, on-farm research in western Idaho showed that rapeseed green manures decreased soil populations of rootlesion nematodes to a greater extent than did sudangrass green manures. Fall sudangrass should be plowed down after it is stressed (i.e., the first frost, stopping irrigation). Winter rapeseed and canola should be incorporated in very early spring. (Cardwell and Ingham, 1996)
So it also looks like a simple winter ‘cover crop’ of mustard or canola/rapeseed can kill the buggers too. As I’m rather fond of some kinds of mustard greens and have sometimes thought of growing my own seed mustard, that would not be much of an imposition at all…
The best rotation to control the Columbia root-knot nematode in potatoes involves planting a summer non-host crop, followed by a winter cover crop (rapeseed) incorporated as a green manure. Non-host crops include supersweet corn (Crisp and Sweet 710/711), pepper, lima bean, turnip, cowpea, muskmelon, watermelon, squash, rapeseed, canola, mustard, and sudangrass (Trudan 8, Sordan 79). (Ingham, 1990)
For root lesion nematode control on potatoes, researchers found that forage pearl millet (Canadian Hybrid 101) and marigold (Crakerjack) as rotation crops with potatoes resulted in fewer root lesion nematodes and increased potato yields than rotation with rye. (Ball-Coelho et al., 2003)
Now here we have the choice of a corn rotation, or peppers, lima beans, turnips, melons, squash…. My God, you could make a whole garden just out of those things!. Now, each nematode type hits different plants to a different degree, but still… It looks like with a little care you can have a patch that gets the Chicken Scratch and fallow, then corn, then a nematode susceptible crop, then marigolds, with a winter mustard, repeat. (or any of dozens of other rotations).
I found that “pearl millet” particularly interesting as Millet is a very low water crop and one of the few cereals that can be grown as a perennial and is generally VERY hardy to all sorts of things. I’ve thought of ‘giving it a go’ just to see if I can have a non-irrigated grain here in California (where we don’t “do” rain for 1/2 the year…)
So, nematodes getting your tomatoes and potatoes? The Marigold looks like it can help:
Tomatoes planted two weeks after African marigolds (Tagetes erecta) were disked into the soil showed a 99 percent reduction in root-lesion nematode damage compared to a tomato-tomato or fallow-tomato rotation. (Grossman, 1999) The French marigold cultivar “Single Gold” provided 99 percent control of nematodes in Dutch tests. (Ogden, 1997) Burpee Seed Co. has carried a French marigold variety known as “Nema-gone.” The most effective marigold cultivars are those that germinate quickly, grow vigorously, and have deep root penetration. Cover crops exhibit tremendous variability in their susceptibility to or suppression of the four major types of plant-parasitic nematodes. For example, cover crops that suppress root-knot nematodes may be susceptible to sting nematodes. It is important to identify the nematode species in the field—and know what their plant hosts and antagonists are—before planning a cover-cropping strategy.
Though they do note that it may depend on what kind of nematodes you have…
That article goes on into such processes as soil heating and application of various beneficial bacteria. Well worth the time to read it if you have a serious nematode issue…
This article, in comparison, says almost nothing; but it does have some really nice pictures of a row of marigolds being grown as a ‘cover crop’. I never realized they could grow that high!
Our research on cover crops has focussed on the use of marigolds (Tagetes spp.) to control root-knot nematodes (Meloidogyne spp.). In greenhouse experiments marigold varieties were identified with high efficacy in nematode control. Subsequent field tests showed that selected marigold varieties, grown prior to a susceptible crop, lowered nematode populations and increased yields similar to soil fumIgation.
It does point out the need to pay attention to which plant works best on what nematode… so if one strategy doesn’t work (or stops working after a while), ‘mix it up’ with a different cover crop strategy.
If you have a nematode problem, it looks like a “keep changing the plantings” strategy works. It’s about “population control” and starving the little suckers during part of their life cycle. Knowing what they can’t eat, or live on, and what eats them (the chitin eating fungus…) helps too.
The especially good news is that many of the things they can’t stand are crops I’d love to eat. From corn and millet to Sorghum and a mess ‘o Mustard Greens. Even Collards, as a cruciferous vegetable, ought to do well.
So it looks to me like you need to do a bit of thinking about when and where to put things like tomatoes and potatoes; but if you let the land run to Marigolds while doing that thinking it ought to work out just fine…