The Source of Quintozene Residues in Ginseng
Quintozene, sometimes referred to as PCNB (for pentachloronitrobenzene), is a commonly applied fungicidal treatment for control of a garden rot that affects many plants during cool, wet months. It has been widely used to protect ginseng crops; until recently, those involved in marketing the crops and producing finished products were unaware of its use. Beginning in 1998, tests conducted in the U.S. showed that some imported ginseng roots had detectable residues of this fungicide. While quintozene is permitted for American ginseng cultivation in Canada, it is not registered for use in American ginseng cultivation in the U.S.
The U.S. Environmental Protection Agency (EPA) currently describes quintozene as a potential health hazard, given its widespread use on a multitude of crops, which leads to potential for cumulative exposure. While the amounts detected in the ginseng roots did not lead to a product recall because both government officials and industry leaders agreed that the amounts posed no health threat, steps have been taken to remove quintozene from the supply of imported ginseng.
Plant Products Company Limited (Ontario, Canada) is the supplier of the fungicide "Plant-Prod 0-0-6 with 15% quintozene." A passage from their promotional literature states:
Plant-Prod 0-0-6 delivers effective control of Rhizoctonia [a fungus responsible for stem rot and root rot] for ginseng, in a granular form. Plant-Prod 0-0-6 is easy to apply through any field fertilizer applicator, and has very little dust. The proven performance of quintozene combined with a uniform granule offers ginseng growers the best in-season protection for ginseng gardens.
The literature further states:
Weather conditions this season will leave gardens at risk of Rhizoctonia infections over the cooler months. At the present, growers have only one active ingredient to use for Rhizoctonia control. Quintozene is registered for use on ginseng in Canada.
Quintozene is also recommended by the company for treatment of stem rot on African violet, begonia, carnation, chrysanthemum, poinsettia, snapdragon, and similar bedding plants. Quintozene is approved in the U.S. and other countries for several food crops, being commonly applied to beans, peas, peanuts, cruciferous vegetables, corn, garlic, onions, lettuce, peppers, potatoes, tomatoes, mushrooms, and cucumbers. The residues on these foods are generally low, usually well under 1 ppm, except for mushrooms (up to 10 ppm). Quintozene is also used on non-edible plants, including cotton, decorative garden plants, and grass (e.g., on golf greens).
The usual method of using quintozene for ginseng farms in Canada is to apply a high-volume spray (with 9 kg quintozene per hectare, diluted in about 4,000 liters of water) only once per year, when the ginseng rootlets are transplanted to the new bed from which they will be harvested. To avoid having residues on the herb material that is sold, it must not be applied within two years of harvesting the crop (a requirement for ginseng cultivators in Canada).
This fungicide is used worldwide and has been a staple of ginseng cultivation in the Orient for the past thirty years, ever since ginseng cultivation became a major international business. Large scale production of Oriental ginseng cultivation first developed in Korea (1). From a stable cultivation area of about 1,000-1,500 hectares during the 1960s, the growth area increased to nearly 8,000 hectares (over 3,000 acres) in a burst of development from 1970-1975. In 1975, Korea exported $42 million dollars worth of ginseng. The need for quintozene under these circumstances becomes obvious: ginseng crops can readily be destroyed by fungal infections. About half of the Korean ginseng yield was destroyed by root rots in 1965 and again in 1977, leading to widespread adoption of the fungicide.
Rhizoctonia thrives in cold, wet weather, which is characteristic of the fall through spring months in most ginseng cultivation areas (primarily located in the northern, inland areas). When crops are no longer grown on the infected soil, the level of Rhizoctonia slowly declines, still feeding off remnants of the old crop and on any grasses that may grow on the soil. The land must remain essentially barren for a decade or more before the soil can once again be used for growing a crop susceptible to this organism; unless, of course, the organism is destroyed and continually controlled by fungicides such as quintozene.
Rhizoctonia is one of the most important soil pathogens worldwide. The International Society of Plant Pathology has established a Rhizoctonia Committee to encourage progress in understanding the organism and the plant diseases it causes, and to find ways to control it. Rhizoctonia causes numerous diseases including damping-off, seedling stem canker, tuber and root rots, and leaf blight and rots on vegetables and fruit. The main species is Rhizoctonia solani, named for its attack against potatoes (Solanum tuberosum). The problem of Rhizoctonia growth in ginseng fields has been studied in detail (see Appendix 1).
Although Rhizoctonia is frequently mentioned in this article, ginseng is also susceptible to other fungal infections, such as Phytophthora and Alternaria, causes of leaf blight, which can be controlled by using other fungicides. For example, the fungicide Rovral (iprodione) is approved for use in the U.S. in treating Alternaria blight, one of the diseases that attacks American ginseng grown in the East Coast area; hexachlorobenzene (HCB, chemically similar to quintozene) is approved for treatment of Phytophthora in some U.S. crops, such as alfalfa. Other important ginseng fungal pathogens are Cylindrocarpon destructans, which can rot the ginseng roots at any age, and various species of Fusarium and Pythium that cause pre-emergence damping off and post-emergence seedling root rot. Quintozene is used to treat these root fungi.
Americans were alerted to the presence of quintozene residues on ginseng when an herb supply company (Hauser Chemical Research Incorporated, Boulder, Colorado, a conglomerate of Botanicals International Extracts, Inc., ZetaPharm, Inc., Hauser Laboratories, and Shuster Laboratories) sent a sample of ginseng for testing to PharmaPrint (a California laboratory). PharmaPrint detected quintozene and alerted the U.S. FDA. The event soon showed up in news reports, such as a CNN item dated May 21, 1998, titled: "Company says Ginseng Batch Contaminated."
After this story appeared, www.ConsumerLab.com, a laboratory that does testing of natural health care products and provides results on the internet (there is a subscriber fee), performed tests on ginseng products. They reported that:
In April and May 2000, ConsumerLab.com purchased a total of 22 brands of Asian and American ginseng products....Seventeen of these products were Asian (labeled as Panax ginseng, Asian ginseng, Chinese ginseng, or Korean ginseng), four were American ginseng [Panax quinquefolium], and one was a mixture of Asian, American, and Siberian ginseng. One of the American ginseng products made of root powder was immediately eliminated from further testing....The remaining twenty-one products were tested....Eight products contained unacceptable levels of both quintozene and hexachlorobenzene [HCB]. Two of these products had levels of these pesticides more than twenty times the allowed amount. None of the products tested surpassed the limit for the pesticide lindane....Among the eight Korean ginseng products contaminated with pesticides three also had low ginsenoside levels and two others had high lead levels.
The report ended up focusing attention on Korean ginseng in terms of pesticide contamination, as well as other problems. However, some American companies began testing their ginseng products and it was soon found that quintozene contamination, though at low levels, occurred in some samples of Chinese ginseng as well (the ginseng tested earlier by Pharmaprint was reported to be from China). Other fungicide residues, such as HCB, and some pesticide residues have also been detected in ginseng roots from China and Korea.
Although only tiny amounts of quintozene remain on ginseng after it is harvested, some ginseng samples had been found to have more than 20 ppm of quintozene (ConsumerLab.com had used a passing standard of 1 ppm for quintozene; 0.1 ppm for hexachlorobenzene). The amount of quintozene ingested by a consumer is quite small because of the small amount of herb material usually recommended.
The U.S. FDA has set as the standard that ginseng be quintozene free, defined as having less than 0.01 ppm, the current limit of detection. Canadian ginseng growers usually have to avoid using this product if they intend to sell their ginseng crops to American herb manufacturers. Despite the widespread use of quintozene on ginseng crops in the Orient, most roots tested do not show any significant levels because the farmers acted responsibly and ceased using it long enough prior to harvest so that any residues are miniscule. However, the new U.S. standard, along with refined testing methods, makes it difficult to attain a quintozene-free ginseng product without completely avoiding the use of quintozene during ginseng cultivation.
The problem of rot developing at ginseng farms is a major one that threatens the entire harvest. When a forest area is first cleared for ginseng cultivation, there is little danger of the problem. However, after one crop of ginseng has been harvested, the area is usually contaminated with Rhizoctonia and other pathogenic fungal mycelia. A high risk of crop failure is present for any further cultivation on the same land, at least if fungicides are not used. One obvious method of avoiding this problem-constantly finding new forest land for ginseng crops and then moving on-is impractical and undesirable, as it involves forest destruction and instability for the workers. In China, clearing new forest land is now restricted, so ginseng farmers are not permitted to remove trees to make new beds that have very low levels of potentially pathogenic fungi.
Non-chemical controls are the most important area of investigation. First and foremost, ginseng farms must be established in areas where the soil conditions are correct and where weather conditions are frequently favorable (for avoiding stem and root rots). It is not suitable to simply turn any piece of available farmland into a ginseng farm, as is suggested when individuals and agencies promote ginseng farming as a good means of developing a successful cash crop. Proper ginseng cultivation is very labor intensive, involving considerable manipulation of the soil. In addition, seeds need to be treated to eliminate Rhizoctonia, any added soil must be heat sterilized, and all tools must be kept cleansed. Irrigation water must not carry the disease organism from one area to the next. Ginseng cultivation should not be viewed the same as cultivation of other crops, due to the unique requirements for long-term growth (typically 5-6 years) in conditions that can easily favor root rot.
Second, the soil is to be made alkaline to prevent growth of pathogenic fungi, using soil amendments of calcium carbonate, such as from oyster shell powder or ground bones. Pamela Dixon, in her book Ginseng (2), relays that in Korea the finest fertilizer came from old Korean houses made of clay. The walls, weathered over many decades, were pulverized and scattered over the beds; thus providing an alkaline material. Nitrogen-based fertilizers need to be minimized or avoided, as these stimulate the growth of Rhizoctonia. A fertilizer called yakto was traditionally used in Korea, made by fermenting foliage of broad-leaved trees, with a small amount of grass, cotton seed cake, soybean cake, and defatted rice bran; tree ashes or chimney soot were also added (these serve as alkalinizing agents). Testing of various soil amendments to control root rots was carried out by the College of Agriculture at Seoul National University. From an original group of 9 possible amendments, three looked promising: crab shell, cow bone, and pig feces. These soil amendments increased the amount of various non-pathogenic soil fungi, resulting in significant reductions in the pathogenic populations. By using these natural soil amendments, it was possible to reduce the frequency of, but not eliminate, root rot in ginseng plants (3).
Third, soil drainage must be checked regularly and adjusted to assure that the soil is not retaining too much moisture, as this also encourages the growth of the organism. The usual method of ginseng cultivation involves moving the nursery roots to a new and much larger bed after the first two or three years of growth, thus helping to avoid development of fungal rots by providing fresh soil (sterilized by heat and prepared to have good drainage) and a larger growing area to avoid crowding.
Fourth, ginseng plots must be relatively small, so that a huge investment is not threatened by the presence of a patch of rot. Otherwise, the cultivator will be forced to turn to fungicide chemicals to assure that the whole crop isn't lost. There are numerous other details that a ginseng cultivator must give attention to in order to have his crop be successful, but the attempt to make a large patch successful is fraught with risks.
There may be some natural antifungal agents that can be applied to the soil to prevent Rhizoctonia and other fungal growth; suggestions have included extracts of chamomile and clove. However, unlike quintozene, such natural antifungals are rapidly biodegraded and need to be applied repeatedly to have a good effect.
Following is the story of an American ginseng cultivator, A.R. Harding, who grew his plants long before quintozene was developed and before Rhizoctonia was found to be the culprit most frequently damaging the plants (4):
The writer began the cultivation of ginseng in 1899, or 14 years ago. I have had a very wide range for observations along the line of cultivation, propagation, and marketing of this valuable root. Besides visiting hundreds of gardens, I have had separate beds of wild roots in my garden arranged side by side, each bed containing roots from one state only....
It is the history of nearly all wild plants that when brought under cultivation they develop a weakness and liability to disease. Ginseng has been no exception. This has been brought about, in part, by a change of environment, but of all the causes that have brought disease to the ginseng plant, I think the greatest single element has been too high feeding. Naturally, this plant grew among the roots of trees and other large and strong plants. These sapped the fertility from the soil and ginseng was fed sparingly and made a very slow growth. Taking the plant from this condition, and giving it rich garden soil with nothing to steal the fertility from the soil, and then covering the beds every fall with from one to three inches of manure, proved too much and so enfeebled the constitution. For a time it looked as if the plant would succumb to disease, but for two to three years now the growers have been getting the upper hand again and I believe soon everything will be moving along smooth again....
Its home is in the forest among the trees and many tall and vigorous plants. This is not an acquired habit or one of recent origin....Let us look at some of the conditions under which this habit compels ginseng to live and grow. First, in shade, not absolute, but in the main it is shielded from the direct rays of the sun. It has, however, light and air; the shade, you will bear in mind, is very high up, sometimes not less than 75-100 feet from the plants. The shade is not all at one level, some trees are tall and some shorter, some branches a hundred feet high, others close to the ground. This, you see, gives good air circulation as well as shade far better than if all the shade were on one level.…
Ginseng is rarely found wild in damp places or where stagnant water is near, although it is sometimes found very close to running water. While the pond lily may flourish in stagnant water, it is not the habit of ginseng to use such water, and if forced to is made sick by so doing. So, we have another hereditary habit of locating on well drained land. Ginseng grew in small plots and was not huddled together with acres of its own kind to breed disease and epidemics. The soil, made mellow and porous by the roots of larger plants, gives us a hint of the needs in that direction.
Still another habit that some of our best growers have been determined to overlook is the fact that the natural home of this plant is not among evergreens, but among the maples and beech and basswood trees. These rarely predominate on very sandy soil, so I infer that the habit of this plant is to seek a heavier soil than sand.
In this nearly century old presentation, we are provided with several key factors in assuring ginseng's health in cultivation that still apply today if one wishes to avoid using fungicides: small plots, not overly fertilized, well-drained soil, shading that is not all at one level so as to assure proper air flow and lighting. The damage to ginseng, now known to be frequently caused by Rhizoctonia and other soil fungi, is summed up by Harding in this comment:
The young plant is very weak and of remarkably slow growth. It thrives only in virgin soil, and is very choosey in its selection of a place to grow. Remove the soil to another place or cultivate it in any way and it loses its charm for producing this most fastidious plant.
As to a successful ginseng farm, Harding relays this report from another ginseng cultivator:
We have at present, writes a grower, in our ginseng patch about 3,500 plants and will this year get quite a lot of excellent seed. Our ginseng garden is on a flat or bench on a north hillside near the top that was never cleared. The soil is sandy loam and in exposure and quality naturally adapted to the growth of this plant. The natural growth of the timber is walnut, both black and white, oak, red bud, dogwood, sugar maple, linden, poplar, and some other varieties. We cultivate by letting the leaves from the trees drop down upon the bed in the fall as mulch and then in the early spring we burn the leaves off the bed. Our plants seem to like this treatment very well.
By contrast, ginseng farms in the Orient are typically on flat cleared land, with thatched shading at a constant level, and with many tens of thousands of ginseng plants. The reason ginseng is usually not cultivated two times consecutively on the same land is not, as traditionally stated, that the plants drain the soil of nutrients, but that fungal pathogens becomes prevalent in the soil and prevent young ginseng from growing. For the same reason, other root crops are also not to be planted where ginseng once grew. Therefore, it is not too surprising that the farmers in the Orient have had to turn to use of quintozene and other fungicides.
In North America, there was a rush to develop profitable ginseng farms in the late 19th Century, but in 1904 hundreds of ginseng farms were wiped out by Alternaria blight (a similar blight halted the development of ginseng farms in New York in 1910). Farmers were first forced to grow ginseng under more natural conditions, but later most growers turned to the use of fungicides that allowed large-scale farming, as is now done in Canada. Today, Canada produces 2,300 tons of ginseng roots per year from nearly 6,000 acres of cultivated land, mainly in Ontario and British Columbia. More than 60% of the root material (about 1,400 tons) is exported, with a value of about 42 million Canadian dollars. The United States produces somewhat less ginseng, about 1,000 tons of cultivated ginseng is exported each year.
In China, some ginseng farmers have also turned to relying on woods-grown ginseng to avoid use of fungicides (5). The plants are started at the farm in soil that has been carefully heat sterilized, but after 2-3 years, the rootlets are transplanted into the forest under Tilia amurensis (linden) trees. This method helps avoid the use of fungicides, but also greatly reduces the ginseng yield, producing more costly roots.
The following is a summary of the problem of Rhizoctonia described by Dr. Richard D. Reeleder, of Agriculture and Agri-Food Canada:
Rhizoctonia solani is a soil-borne fungus that occurs worldwide. The fungus causes a variety of symptoms on a variety of crops, including seed decay, damping-off, crown rot, bud rot, and stem cankers. Different strains of the fungus exist, each with different preferences for host, optimum temperature, etc. Although there is a great deal of information about Rhizoctonia on other crops, very little information exists about Rhizoctonia diseases on ginseng.
Rhizoctonia disease on ginseng often appears early in the growing season. The fungus commonly causes damping-off in the seedling year. Crown rot can also be caused by Rhizoctonia and appears to be most severe in 2- and 3-year-old gardens. When ginseng seed is infected, or when the fungus in the soil invades the germinating seed, the plant can be killed before emergence. Conditions such as cold wet soils, which slow plant germination and growth, prolong the time that seedlings are susceptible to this type of damping-off. Damping-off can also occur after the seedlings have emerged from the soil. The fungus attacks the stem at the soil level, causing the seedling to collapse. Because a number of different disease organisms can cause damping-off symptoms on ginseng, the presence of Rhizoctonia can be confirmed by using a microscope to examine diseased tissue for characteristic strands (mycelium) of the fungus. The hyphae are septate with right-angled branching. Spores are rarely produced.
The bud in the crown of the root apparently becomes infected sometime during late fall or early spring. If the bud is infected at this time there is little chance that the plant will recover and initiate a new bud. The diseased area appears rusty-orange in color, and eventually the entire crown is infected. Infected plants do not emerge in the spring. Rhizoctonia usually overwinters as mycelium or sclerotia [hardened masses of mycelia that are resistant to fungicides] in the soil or on infected roots. The disease may invade and infect ginseng seed in the seed-box and be carried into new gardens on the seed. The fungus is present in most soils, and once established, remains there indefinitely. The fungus spreads with rain, irrigation or flood water, and with tools or anything else that carries contaminated soil.
In general, Rhizoctonia diseases are more severe in moderately wet soils rather than soils that are waterlogged or dry. Thus the mulched, raised beds used for ginseng production are ideal for disease development. Infection of young plants is most severe when plant growth is slow due to adverse environmental conditions. Growth of the fungus is favoured in soils high in nitrogen. The optimum temperature for most strains of Rhizoctonia is between 15 and l8ºC, although some strains are active at higher temperatures. No information exists on the optimum conditions for infection of ginseng. Infection of the bud at the crown of the root appears to take place in late fall or early spring. However, further research is required to study when and how Rhizoctonia infects ginseng.
Management practices are important for control of Rhizoctonia because disease-resistant ginseng cultivars are not available. Fumigation with appropriate products can reduce soil populations of Rhizoctonia and other soil-borne organisms. At seeding time, be careful not to contaminate fumigated soil with unfumigated soil. Use only clean, healthy seed from a reputable source. Avoid over-crowding plants caused by high seeding rates and avoid excessive nitrogen applications. Restrict movement of contaminated soil and surface water between ginseng gardens. In the spring, keep shades back as long as possible before plant emergence. This will help the soil to warm up and dry out, and allow seedlings to emerge more quickly. Rhizoctonia diseases of several crops can be managed through the use of fungicides. Where fungicides are registered for control of Rhizoctonia on ginseng, refer to the product labels for details.
Figure 2: Rows of ginseng plants in full fruit, just prior to harvest after 4-6 years of growth (Korea).
Figure 3: Ginseng harvest at small farm made from a clearing in the woods (China).
Figure 4: Forest-grown ginseng; the low plants are ginseng after about three years of growth (U.S.).