From the October 2001 issue of Oregon Tilth
Garden Symphlans Infest Willamette Valley Soils:

Oregon Tilth Growers Share Strategies

Imagine a critter that thrives in the best organic tilth and emerges cyclically as one of the most devastating crop problems in our midst. Furthermore, imagine this beastie not only consistently resists all tried control measures but that most of the information we have about it is anecdotal and highly contradictory.
Meet the garden symphylan (Scutigerella immaculata), sometimes called the garden centipede, a small, delicate, soil-inhabiting arthropod, of the class symphyla, which are related to members of the class insecta.

“Symphs” are not classified as insects because insects have three body parts (head, thorax and abdomen) while symphs have many—a head, a trunk and, with mature specimens, 14 segments and eight to 12 pairs of legs. The class symphyla are extremely common inhabitants of soil in all parts of the world. (“Symphs” and “symphlans,” in common and agricultural context always refer to the garden symphlan, and not to all symphlans.) No in-depth systematic work has been done in Oregon into species distributions. Some can consume more than 20 times their own weight in vegetable matter in 24 hours. They are translucent to milky white, and range in size from barely visible to the average eye, to the length of a long eyelash. They move like quicksilver, crawling across an outstretched palm in about five seconds. They are “decomposers” that feed on decaying organic matter and on the roots of a very wide range of living crops and other plants, including weeds. (Many members of the class symphla are strictly decomposers, but garden symplans feed on living plant material (likely preferentially), making them omnivores and not decomposers.

Symphs lay clusters of white eggs about 12 inches deep in the soil. According to research done by Ralph Berry at Oregon State University (OSU), “Total development time from egg to adult is about 160 days at 50 degrees, 87 days at 68 degrees and 53 days at 77 degrees. The number of generations per year has not been determined because of the overlapping development of the various stages in the field. Since it requires about three months to complete development from egg to adult, there is at least one generation each year and ample time for two complete broods. “Although symphs’ reproductive capacity appears closely related to the prevalence of living plant matter, they can survive long periods on organic matter. Laboratory experiments have shown they can live up to five years in a petri dish, with no live plant material added. Very little is known about the way they move through the soil. Too fragile to burrow their own tunnels, they appear to crawl through the soil in the trails of other soil dwellers. Research has shown they can move laterally up to 30 centimeters a day but appear not to move long distances over short periods.

Evidence may yet show that symphs are integral to soil health. Indeed, some research suggests that symphs are far more common in the soil than we imagine. Typically though, symphs are noticed only when their numbers explode within an agricultural cropland, when they pass a population threshold of sorts and turn their attention to the roots of germinating seeds and young transplants, interfering with the plants’ ability to take up water and nutrients. They also cause indirect damage by pitting roots, opening them to secondary infections by other soil pathogens. Often it’s only when faced with stunted and dying crops, that growers become alerted to the presence of symphs. OSU researchers have said when there are more than seven or eight symphs in a shovel of soil, they’ve crossed a threshold into “crop pest.”

Causes of problematic symph infestations are, for the most part, unknown. “I think that it is significant that they inhabit good soil,” says biodynamicist Dennis Klocek, “This makes them problematic for organic farmers who do manage to get some tilth in the soil they are working.” It’s a view echoed by Amigo Cantisano of Organic Ag Advisors: “I’ve come to think of it as an ‘OFD,’ organic farm disease, as I get so many inquiries about them from organic growers and only very rarely from conventional growers, which leads me to believe that the high rates of raw to partially decomposed organic matter additions by organic growers is the main stimulant to these pests.”

Some growers believe imported manure carries the symph. Many think poultry manure is a common symph spreader. But, “Actually, the anecdotal evidence I’ve heard is that symphs prefer horse manure,” says Garth Kahl, a grower and certifier for Oregon Tilth. “The reason is that they prefer coarse, un-broken down organic matter, and horse manure seems to have a lot of it. If there is any link with poultry waste it would be because of the rice hulls normally found in this material and not the poultry manure, which has very little undigested organic matter.” But when symphs first became an issue in Midwestern farmlands, growers there put it down to the removal of manure from fields.
In truth, we have few certainties to go on says, Jon Umble, a graduate student at Oregon State University who may know more about symphs than any other two-legged. “So much is not known about what is going with symphs in agroecosystems,” he says. “As to the historical trend, it’s hard to say what’s going on since not many records are kept on symph damage (in organic systems). We know symphs have been a major problem in Oregon since the early ‘30s.” But as with many agricultural pests, the detailed ecological work of the ‘30s and ‘40s fades into pesticide trials in the ‘50s and ‘60s. “The use of pesticides has been effective to some degree in conventional systems, but many conventional growers have perennial problems with symphs also,” says Umble. “In California, symphs were also a huge problem in the ‘30s, and have only really been recognized as a major pest again in organic systems in the past 10-15 years. Many growers and extension agents who haven’t seen symph damage may misdiagnose what is going on in the system.”

Conflicting opinion typifies the symph issue. Mark van Horn, manager of the Student Experimental Farm at UC Davis and a participant in a recent Organic Farming Research Foundation’s (OFRF) symph study, has been working to monitor and control symphylans since 1998. At the 2001 Eco-Farm conference, he co-hosted an open forum on symphs. A room packed full of growers was asked to volunteer what they had tried, what had worked and hadn’t. “The most interesting result of that for me was that every single thing that someone tried ‘with success’ someone else in the room had tried ‘without success.’ Given the complexity of symph movement and population dynamics, I’m not surprised.”

He continues, “I’m a firm advocate of listening to farmers and gardeners--that’s primarily how we decided on the treatments in our studies. However, with symphylans, my experience has been that anecdotal evidence has not led to reliably predictable approaches.” Indeed, it’s almost a truism that studies outlining field tests with symph controls tend to conclude along the lines of, “No treatments reduced symphylan populations by an agronomically significant amount.”

Micro-patterns of symph infestation resist easy analysis. They are difficult and time-consuming to sample. “Symph patches” tend to be circular and cover areas of a few feet to a number of acres. The damage they inflict is consistent across different plant types where a variety of crops are planted in close proximity. They appear to have a very wide host range. Although some evidence suggests symphs are found more often in systems with high organic matter levels that have been farmed or gardened for a number of years, high symph levels have also been seen in land taken directly out of non-irrigated and irrigated pasture. In other words, symphs seem to appear in high numbers in relatively undisturbed soil systems, too.

The seeming random changes in patterns of symphylan infestation make field studies very difficult. “I have seen fairly dramatic shifts in the location of these hotspots, from season to season,” says Umble, “And are we looking at the movement of populations, or fluctuations of populations in place? We don’t know.”

Symph populations may also move up to 1.5 meters vertically in the soil in an annual cycle. They molt throughout their lives. Just prior to molting, they leave root systems and go into a non-feeding stage deep in the soil. Although the seasonality of this cycle is generally consistent, significant annual variation may occur. For example, in some locations with hot summers, surface symphylan numbers are typically high in the late spring but decrease dramatically as feeding cycles, lack of moisture and rising summer temperatures force them toward cooler soil. However the timing of this decrease can vary by several weeks from one year to the next. Even so, research has shown that it is not possible to predict precisely when the symphylans will leave the soil surface for deeper layers.

Some growers play to symphs’ vertical migration patterns with muscular control strategies. As one farmer put it, “We wait until they’re close to the surface, then rototill the shit out of them.” Before planting strawberries, Carl Berg of Berg’s Berries tries a similar tactic. “We will rototill the upper few inches two to three times over the course of a few weeks in an effort to kill as many as we can.” Amigo Cantisano says, “Two to three tillings a week for three to four weeks makes a big dent,” and Jon Umble: “I hate to say it, but tilling does seem to be one of the few tactics that shows some success.”

Then again, Mark van Horn suggests that the elevator ride of symphs through the soil ensures that the relative success of most control measures is extremely difficult to measure, particularly over the long term. “In general, the numbers of symphs feeding near the surface fluctuates dramatically each year. Depending on the timing of an attempted ‘control’ strategy, these fluctuations can make our attempts appear successful or unsuccessful, regardless of their actual impact.” The inability of conventional growers to poison symphylans, very delicate critters, out of their fields, suggests symphs may actually flee to safer depths whenever a surface threat proves particularly dangerous, only to re-emerge later. As the OFRF study concluded, “Aggressive soil tillage when there are symphylans near the soil surface may sometimes reduce their numbers by either directly killing some of them and/or by hastening their movement deeper into the soil. However, because symphylans can move rapidly, individuals from below the tillage zone can quickly recolonize the surface, which may limit the effectiveness of tillage.” Umble adds, “The fact that symphs can ‘retreat’ to the deeper soil horizons better than some predators means tillage may be more damaging to predator populations than to the symphs.”

Pat Patterson of the OSU Extension Service in Eugene suggests that summer watering is a large part of the problem associated with accelerated symph reproduction. Umble adds though that symphs can be a problem in very dry soils also, “A sudden problem with symphs in Washington east of the Cascades in the ‘50s was largely attributed to the increased use of irrigation. In general, most of the conditions that are good for plants are good for symphylans. But I’ve seen them in some pretty dry soils, close to the surface. And growing dry-farm (non-irrigated) tomatoes has not appeared to reduce symphylan damage on organic farms in California.”

Umble believes crop rotation may be an important factor in increasing and decreasing symph numbers, saying “Personally, I believe that there is a lot more to the relationship between symphs and their host plants, which is why I have focused my research here. But we are only just at the beginning stages of looking at symphs in a rotational sense, and we don’t have many specifics to speak of. Numbers have already been shown to change following different cover-crops but not significantly enough.”

At this juncture, our understanding of symph eating habits is rather haphazard. One agricultural consultant tells me, “I’ve never seen a problem around tomatoes, not even monocrop commercial growers. It’s the solonaceous plants in general. Scratch the root of a tomato; its exudates are highly aromatic and keep the symphs off. You’ll see symphs around them, but the plants are okay. Corn, I saw an entire corn crop destroyed by symphs a couple of years ago.” The same day another grower tells me, “Corn’s too vigorous for the symphs to get to. Look at the root size. But last year’s tomato crop got nailed.” Jim Leap’s work at the University of Santa Cruz suggests that susceptibility within plant families can differ widely. His experience around solonaceae is that tomatoes, peppers and eggplants can all get hit hard but that potatoes don’t (which conflicts with Seattle Tilth statements.)

Umble believes a plant’s susceptibility may have a great deal to do with its relative immunity to high symph populations and is looking closely at plant vigor as a factor in choosing crops for symph patches. Several observers recommend using transplants that are healthy and well-rooted before transplanting and, where possible, planting early in the spring before the population moves up through the soil and in late summer when the critters move deep again.
“I think there’s got to be some way to manage symphs with bio-control, in conjunction with some other sound agronomic practices,” says Van Horn, “but we don’t have a lead on that.” In the meantime, growers forge ahead on their own. Jim Leap of the UC Santa Cruz farm site says, “Our work suggests symphylan suppression after a potato crop. We still don’t know why, but it works.” Mark Wheeler of Pacific Botanicals experiments with California poppy rotations. At Full Circle Farm in Eugene, beans appear to be a tried and tested response to symph infestation. At Dancing Tree Farms, among other tactics, growers Kris Dicus and Daniel Cameron are experimenting with their own bio-control tea regimen (see box). At Wintergreen Farm, currently home to an OSU symph survey, Jack Gray took a page from Jon Umble, who he saw sampling symphs on his land by using potatoes as bait. On a symph patch, “We laid down a screen, covered it with a half inch of potato mash, covered that to keep the light out, then pulled the mash up two days later. Though we found all sorts of predators, we didn’t see any noticeable number of symphs.” Whether or not the symphs got gobbled, we don’t know - as we go to press, Gray is about to sample for symph populations in the soil. Wintergreen experiments with other approaches, too.

Although confusion reigns, at least one thing seems clear: The symph story holds deep lessons for the organics community that go well beyond our current understandings of agricultural ecology and our relationship to it. Indeed, events may yet show that the unfolding symph mystery resists any “generic” answer, with solutions turning out to be largely predicated upon place and the creative potential of each individual farm ecology and farmer--not a bad thing necessarily.
Detractor and Balance Teas for symph patches

Dancing Tree Farms

In a five-gallon bucket, mix a detraction tea concentrate of a half pound of chrysanthemum flowers, a half pound of marigold flowers, one pound of comfrey leaves, a half pound of nettle leaves, three ounces of chamomile flowers and a quarter pound of willow tips. Let the concentrate sit for 10 days, stirring it periodically. Then add and stir with 45 gallons of water. Make several applications over the course of seven days, at dusk.

On day eight, apply biodynamic preparation 501 at dawn and 500 at dusk.

On day nine, begin applying a balance tea. To prepare the concentrate: mix two gallons of kombucha tea, three ounces of valerian, one pound of comfrey, one pound of leaf mold and a half pound of nettle leaves in a five gallon bucket. Let sit for ten days, stirring periodically. Then add and stir with 45 gallons of water. Make several applications over seven days, at dusk.

Tactics commonly used to reduce garden symphylan damage in organic farming systems

Some management strategies aim to reduce symphylan damage indirectly through tactics such as growing less susceptible plants, improving plant nutrition or manipulating planting dates. Other strategies aim to directly reduce symphylan numbers. Many tactics may produce some reduction in numbers, but no single tactic has been shown to decrease symphylans to agronomically acceptable levels. Sampling for symphylans is vital to successfully evaluating reduction tactics; indirect measures (such as plant health) may be extremely variable. Citations for all studies may be obtained by request from Jon Umble:

Tactic Proposed
Success (in studies)
1. Manipulation of pH Decrease symphs Yes None. Symphylans are able to survive through a wide range of pH
2. Diatomaceious earth Decrease symphs Yes None
3. Shrimp shells Decrease symphs Yes None
4. Brassica residues Decrease symphs Yes None
5. Compost/manure Decrease symphs Yes None. Commonly believed to increase numbers, likely improves habitat, possibly a food source, although symphylans are believed to need living plant material to reproduce
Planting manipulation
1. Crop susceptibility Increase plant tolerance Yes Some. Although symphylan numbers may reach levels high enough to kill plantings of many crops, at some infestation levels crops may vary greatly in their susceptibility. This is probably largely related to vigor. Symphylan numbers that kill direct seeded spinach may not even cause observable damage in crops such as corn and potatoes. It is important to note that though some plants may have a low susceptibility to symphylans, they may provide a good food source for population growth (not necessarily a tactic to lower numbers).
2. Stage of growth Increase plant tolerance No N/A. Along with different crops varying in their susceptibility (above), within a single crop (and variety) plant age (eg. direct seeded vs. large transplants) may be a significant factor in reducing observable symphylan damage.
3. Planting date Plant around feeding cycles No N/A. Some growers have tried to plant either before or after times of intense symphylan feeding (believed to be in mid to late June in Oregon). Surface feeding may also be decreased for a limited period just after an intense tillage event. Incomplete understanding of symphylan feeding cycles and inflexibility in planting dates makes this tactic difficult to implement.
4. Crop rotation Decrease symphs Yes Some. Although symphylans may be long-lived and sustained by feeding on organic matter and microbes in the soil, population fluctuations appear to be related to different food sources provided to them. Symphylan numbers have been shown to be greater after cover crops of mustard (Marteginia) than after cover crops of spring barley (Micah) or winter cereal rye (Wheeler) or spring oats (Monida). In the laboratory symphylan numbers have been shown to increase by two to three times in just 2 months when provided with fresh roots of carrots and lettuce leaves, compared to little to no increase in numbers when just soil or manure were provided. Preliminary evidence from ongoing research suggests that growing a crop of potatoes may sometimes reduce symphylan numbers to low enough levels to grow fairly susceptible crops in the following season.
1. Reducing tillage Increase predators Yes Some. Predatory mites, beetles, spiders and centipedes are all probably important symphylan predators. Efforts to increase predators have been somewhat successful, but increases in symphylans were also observed.
2. Increasing tillage Decrease symphs Yes Some. Tillage may physically crush symphylans as well as destroying their runways. Some growers try to till when symphylans are in the surface-soil to maximize effectiveness. Intensity of tillage is likely a key factor.
Pathogens (also see tillage/predators above)
1. Nematodes Decrease symphs Yes None
2. Fungi Decrease symphs Yes Yes. Decreases of symphylan numbers in the laboratory were achieved with a strain of pathogenic fungi in the late 1960ís. No work has been done in the field and no available products have been tested on symphylans.
Management of non-harvested crops/residues
1. Incorporation timing Remove food source No N/A. Some growers have observed that leaving non-harvested crops, such as beets and carrots in (or on) the soil during the winter appears to increase symphylan numbers to high levels the following spring. This observed increase may occur from providing the symphylans with a high-quality food source for development and reproduction.
Organic pesticides
1. Neem Decrease and deter symphs Yes Some. Reduction of numbers in a lab study, not tested in the field. Pesticides may kill symphylans and/or protect roots at sensitive stages. Pesticides are a key-tactic in many conventional symphylan management strategies.
1. Flooding Decrease symphs Yes Some. Flooding has been used historically in California with some success, not viable tactic in most Oregon farming systems. In the Willamette valley symphylans can be problematic in seasonally saturated soils.
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