Question of the Week
Answer: Historically, the horticultural literature and government production bulletins on watercress were geared to field production in flooded beds. However, hydroponic production—indoors or outdoors—has emerged as a modern production method. The following material is divided into two parts: 1) standard outdoor production methods and resources, and 2) greenhouse and hydroponic methods and resources. Please note that cultural and post-harvest practices regarding watercress will be similar for outdoor and greenhouse production systems.
Outdoor Watercress Production
Watercress, Nasturtium officinale (synonym Rorippa nasturtium-aquaticum), is an aquatic, succulent, leafy plant in the mustard family (Cruciferae). It is a perennial plant but can be grown as an annual. Watercress grows wild in clear streams flowing through limestone formations in many parts of the southern and eastern U.S. The plant thrives in full sunlight and cool water.
Fresh leaves of watercress are used as salad greens and as a garnish. The leaves can be steamed and eaten as a vegetable. Watercress is nutritious, being high in minerals, protein, and vitamins (1).
Production of Watercress
Watercress production methods were developed by market gardeners outside London, England, in the 1800s. A site with a stream flowing across it is the basic requirement for getting into production. Ditches are dug adjacent to the stream, either perpendicular or parallel to the flow of water. The ditches are oriented north and south, if possible, and connected in a "zig-zag" fashion on a gradual slope to allow for water flow. More elaborate systems include side-by-side beds with wooden or concrete dikes and walkways.
Before watercress is established, the soil in the bottom of the trenches should be prepared much the same as a regular vegetable garden by adding several inches of compost and then tilling it in and raking it smooth. The bottom of the ditches is then filled with a half-inch of gravel to provide an anchor for the plant roots. Some growers in the northeastern U.S. use oyster shells for this purpose (2).
Commercial plantings of watercress are either direct-seeded or established in seedbeds and then transplanted (3). The soil should be slightly moist, with no water flowing at the time of planting. Seeding rates vary, but an average is around 1 lb. per 6,300 sq. ft. As the seedlings develop, water is let into the bed, but not enough to cover them. Seedlings 2 to 3 inches tall are big enough to transplant. Cuttings from wild patches of watercress can be used to establish beds as well. Seedlings and cuttings are usually transplanted to about 6 inches apart each way. Beds planted with seedlings started in the spring or from early summer cuttings produce a crop by late summer or autumn.
The primary watercress harvest is between March and October when the leafy crop grows above the water. The tops of the plants are cut by the handful about 6 inches below the tips and then gathered into bunches. Under favorable growing conditions, regrowth of the tops allows harvest about a month apart. In the winter watercress grows under water. Watercress can be pulled for harvest with the roots intact during this period, thinning the stand in the process. The roots are cut off before marketing the bunches.
In the article "Nature's Hydroponic Harvest" from The New Farm, listed below, Ohio farmer Dave McCoy describes his system of extending the harvest season by using a plastic mini A-frame greenhouse that sets directly over the spring.
Watercress can also be propagated and grown on a small scale in moist soils, beds, or pots. For home consumption, Taylor's Guide to Vegetables and Herbs (4) suggests growing watercress directly in 5- to 7-gallon containers in moist, neutral pH soil of moderate to high fertility. Johnny's Selected Seed Catalog (5) gave similar suggestions.
Storage and Shelflife
Storage and shelf-life of watercress factor into the marketing and handling of this highly perishable salad green. According to the USDA:
The high perishability of watercress makes prompt handling and refrigeration imperative. The leaves of watercress wilt and become yellow and slimy when improperly handled. Watercress should be precooled promptly after harvest, either by hydrocooling or vacuum cooling, and stored at 32° F. with high humidity (95 to 100 percent). It is bunched and usually packed in alternative layers with flake ice. Watercress stored at 32° F. in waxed cartons with top ice holds up well for 2 to 3 weeks. A similar storage life is possible by using perforated polyethylene crate liners and package icing to minimize wilting. Naked bunches of watercress are highly perishable, even at 32° F., and may keep only 3 or 4 days. In watercress, a 15-percent weight loss will cause only a trace of wilting, and a 40-percent weight loss will cause moderate wilting (6).
In research conducted by the United States Department of Agriculture, watercress held up well at 32° F. and 95% relative humidity for up to 4 weeks in perforated polyethylene bags, but only 4 days in naked bunches. At 68° F. and 60%relative humidity watercress held up for only 2 days in polyethylene bags and 1 day in naked bunches. Using container storage and top ice, watercress held up well for 2 to 3 weeks (7).
Two major diseases affect watercress. Crook root is a waterborne fungus (Spongospora subterranea f. nasturtii) that causes swollen and curved roots, stunting, and breakage of the anchor roots. The addition of zinc to the water reportedly controls the problem. Turnip mosaic virus is spread by several types of aphids, and can be controlled through seed propagation and insect control.
Many areas where watercress can be grown fall under the federal definition of a "wetland" and are subject to stringent restrictions. It may be necessary to apply for a wetlands permit from the Army Corps of Engineers. A farmer who modifies a wetland without a permit could be liable for all restoration costs.
While farming practices in wetlands are not regulated per se, dredging and filling operations are, so essentially any earth moving requires a permit. There may be state and/or local regulations governing activities in wetlands, in addition to federal regulations. Even wetlands previously converted to agriculture may be subject to regulation if for any reason they have reverted to functional wetland characteristics. The Natural Resources Conservation Service can assist farmers with soil-moving recommendations and information.
Watercress, a 53-page British growing guide by C.P. Stevens (8), is a production guide on this crop. It was published in 1983 by Grower Books in London. A common way to find out-of-print books is to borrow a copy through Inter-Library Loan.
Commercial Growing of Watercress, a USDA Farmers' Bulletin published in 1968, describes the climate, water supply, location and construction of beds, establishment, bed management practices, yields, and pest problems involved in watercress production.
Another resource is a bibliography on watercress compiled by the Aquacultural Information Center at the National Agricultural Library. If you have a need for any of the articles listed in this bibliography, check with Inter-Library Loan.
Greenhouse and Hydroponic Watercress Production
Watercress has traditionally been raised in outdoor beds with running water, in regions where spring water is abundant. Little has been published on greenhouse and hydroponic production systems for watercress, but modern production systems routinely employ these methods.
One hydroponic method that seems especially well suited is float bed hydroponics. The fact sheet below from the University of Kentucky provides an introduction to float bed hydroponics of selected edible greens. In the photo, please note the small plastic cups that hold a rooting substrate, which are then placed in styrofoam boards.
Production and Yield of Selected Edible Greens in Hydroponic Ponds
(Float Beds) in a Greenhouse
Robert Anderson, University of Kentucky
Please note the float bed method is widely used to raise tobacco transplants. But, the principles and practices of float bed technology can be equally applied to hydroponic herbs and vegetables. The best places to find resources on float bed production methods are agricultural colleges in Georgia, North Carolina, Tennessee, and Kentucky.
HortTechnology published a review article on watercress in 2001, focusing on the phytochemical properties in watercress that give health benefits. Watercress contains antioxidants, vitamins, and minerals, as well as high concentrations of a chemopreventive specific to tobacco carcinogens. In the notes on culture, it suggests that watercress can be grown in standard hydroponic solutions in beds with running water.
Palaniswamy, Usha R., and Richard J. McAvoy. 2001. Watercress: A salad crop with chemopreventive potential. HortTechnology. Vol. 11, No. 4. (October-December) p. 622–626.
The Growing Edge magazine published an article on watercress in 2003, “What would you grow in water?...watercress.” It features a grower in New Zealand, Glenn Woolsey, who perfected a hydroponic system for watercress production. The production system has worked so well that Woolsey has franchised an additional 24 farms for the production of watercress, which they sell in large volumes to a burdgeoning specialty greens market.
Some details are provided in The Growing Edge article, but it is obviously incomplete. I suppose a grower could pay Woolsey a consulting fee to get specifications and expert advice, or discuss the purchase and establishment of a franchise. Woolsey uses framed beds with a waterproof liner. The article provides essential clues, such as the use of capillary mats, electrical conductivity of the solution, and so forth.
Smith, Rob. 2003. What would you grow in water?... watercress. The Growing Edge. Vol. 14, No. 3. (January-February) p. 81–87.
Acta Horticulturae is the science journal of International Society for Horticultural Science. It published a research article on greenhouse watercress production. Seeds were directly sown into substrates in pots. The substrates that performed well included various types of poorly decomposed peats and a mixture of clay pebbles and peat. The pots sat in basins of slow flowing water, with topdress fertilizers supplying fertility.
Habegger, Ruth, M. Kohl, and D. Fritz. 1989. A cultivation method for Nasturtium officinale (watercress) grown in greenhouse. Acta Horticulturae. Vol. 242. p. 291–295.
Acta Horticulturae has a Web site that can be searched for citations to articles. Two abstracts on watercress production in greenhouses are provided below.
Title : A cultivation method for Nasturtium officinale (watercress) grown in greenhouse.
Call Number : A:PS
Author : Habegger, R.; Kohl, M.; Fritz, D.;
Source : ACTA HORTICULTURAE, no.242:291-295, 1989.
Language : En, Abst. in En,
Keywords : NASTURTIUM OFFICINALE/ WATERCRESS/ INDIGENOUS
VEGETABLES/ GREENHOUSES/ CULTIVATION/ METHODS/ SOWING/
LIQUID FERTILIZERS/ STEMS/
Abstract : Pot experiments were carried out to compare (1) the suitability of different substrates, and (2) crop yields achieved by direct sowing into different sized pots (7, 8, 9 or 10 cm diameter). Since watercress in its natural habitat grows in slowly flowing water, one experiment was set up in a basin with water dammed to a depth of 3 cm flowing through the basin. During cultivation, a liquid fertilizer was applied as required. In another experiment, the pots were placed in
a flowing fertilizer solution dammed to a depth of 2 cm. The harvested crop was assessed for FW, plant length and degree of branching. The highest FW was recorded in plants grown in a substrate mixture of TKS 1 (poorly decomposed peat) + Humosoil (poorly + well decomposed peat); plants in this substrate were well branched and compact. The FW of direct-sown plants increased with pot size, but plants grown in large pots produced thicker stems and had higher nitrate levels than plants grown in smaller pots, and their quality was therefore poorer.
ISHS Acta Horticulturae 614: VI International Symposium on Protected
Cultivation in Mild Winter Climate: Product and Process Innovation
Title: Yield and Quality of Lettuce Grown in Floating System Using Different
Sowing Density and Plant Spatial Arrangements
Authors: M. Gonnella, F. Serio, G. Conversa, P. Santamaria
Keywords: leafy vegetables, ready-to-use products, nitrate, hydroponic
Baby leaf vegetables (rocket, lamb’s lettuce, headless lettuce, endive, escarole, water cress) are mostly requested for mixed salads. Small-size leafy vegetables can be profitably cultivated in a floating system to obtain fresh market products or ready-to-use salads that are arousing more and more interest in consumers. Among hydroponic methods, the floating system is the easiest and cheapest way to produce baby leaf vegetables when soil cultivation is not feasible any more.
When re-circulation of nutrient solution (NS) is used, this system shows high water and fertiliser efficiency and low environmental impact. In the present study two cultivars of lettuce (Lactuca sativa L. var. longifolia) were used: 'Ronda' and 'Amadeus'. The growing cycle was carried out in the greenhouse in March-April 2000.
The growing set-up consisted of benches containing the NS and the floating boards. Two plant densities were adopted: 316 and 620 plant/m2. The latter was obtained using two different plant spatial arrangements. After 40 days of growth, fresh leaf yield was on average near to 6 kg/m2. Leaf dry matter content was on average 5 g/100 g of fresh weight (f.w.) without any differences between treatments. Contents of inorganic anions and cations were determined both in leaves and roots. Nitrate (NO3) content was generally lower than 2,000 mg/kg of f.w. and was not influenced by the treatments. Water consumption was near to 80 L/m2 regardless of plant density, while WUE resulted on average 3.5 g of leaf dry matter produced per litre of water consumed.
1) Simon, James E., Alena F. Chadwick, and Lyle E. Craker. 1984. Herbs: An Indexed Bibliography, 1971-1980. Archon Books, Hamden, CT. 770 p.
2) Pierce, Lincoln C. 1987. Vegetables: Production, Characteristics, and Marketing. John Wiley and Sons, New York, NY. p. 249.
3) Anon. 1987. Growing watercress commercially. The New Farm. July-August. p. 39.
4) DeWolf, Gordon P., Jr. (ed.) 1987. Taylor's Guide to Vegetables and Herbs. Houghton Mifflin Company, Boston, MA. p. 328-329.
5) Johnny's Selected Seeds Catalog. 1996. Albion, ME. p. 32.
6) Hardenburg, Robert E., Alley E. Watada, and Chien Yi Wang. 1986. The Commercial Storage of Fruits, Vegetables, and Florist and Nursery Crops. USDA Agriculture Handbook No. 66. p. 72.
7) Hruschka, Howard W., and Chien Yi Wang. 1979. Storage and Shelf Life of Packaged Watercress, Parsley, and Mint. USDA/SEA Marketing Research Report No. 1102. 19 p.
8) Stevens, C.P. 1983. Watercress. ADAS/MAFF Reference Book 136. Grower Books, London, England. 53 p.
Resources on Standard Outdoor Production of Watercress:
McCoy, Dave. 1987. Nature's hydroponic harvest. The New Farm. July-August. p. 38-40.
Resh, Dr. Howard M. 1993. Outdoor hydroponic watercress production. p. 25-32. In: Proceedings of the 14th Annual Conference on Hydroponics. Growers Press, Inc., Princeton, B.C., Canada.
Shear, G.M. 1968. Commercial Growing of Watercress. USDA Farmer's Bulletin No. 2233. 12 p.
Young, Ann T., and Michelle E. Foster. 1990. Watercress. AIC Series No. 3. National Agricultural Library, Aquacultural Information Center, Beltsville, MD. 12 p.
Resources on Greenhouse and Hydroponic Production of Watercress:
Habegger, Ruth, M. Kohl, and D. Fritz. 1989. A cultivation method for Nasturtium officinale (watercress) grown in greenhouse. Acta Horticulturae. Vol. 242. p. 291–295. (Abstract)
Palaniswamy, Usha R. and Richard J. McAvoy. 2001. Watercress: A salad crop with chemopreventive potential. HortTechnology. Vol. 11, No. 4. (October-December) p. 622–626.
Production and Yield of Selected Edible Greens in Hydroponic Ponds (Float Beds) in a Greenhouse
Robert Anderson, University of Kentucky
Smith, Rob. 2003. What would you grow in water?... watercress. The Growing Edge. Vol. 14, No. 3. (January-February) p. 81–87.
Anon. 1967. Watercress Growing. Bulletin No. 136. Ministries of Agriculture, Fisheries, and Food (Great Britain), H.M.S.O., London, England. 35 p.
Anon. 1995. Decatur Michigan’s Flint Mengel builds upon watercress success. The Great Lakes Vegetable Growers News. May. p. 1, 44.
Belair, Lina. 1992. Watercress, An aquatic treasure. Minnesota Horticulturist. August–September. p. 20–21.
Hoare, A.H. 1924. Watercress and its cultivation. Journal of Ministry of Agriculture (Great Britain). Vol. 30. p. 1147-56.
McHugh, J., S. Fukuda, and K. Takeda. 1981. Watercress Production in Hawaii. Resource Publication 012-11/81. University of Hawaii.
Shear, G.M. 1949. Watercress growing. Virginia Agricultural Experiment Station. Virginia Polytechnic Institute. Blacksburg, VA. 15 p.
Spencer, D.M., and H.H. Glasscock. 1953. Crook root of watercress. Plant Pathology. Vol. 2. p. 19-21.
Answer: In summary, there are two materials that are allowed for rodent control in organic production. However, there are many acceptable methods of control. I have tried to answer your question by commenting on a few key sections of the National Organic Program Standards about pest control that I have pasted in below, and also by providing some general considerations for rodent control. In order to provide you with more specific control options, it is important to identify the problem as specifically as possible. An important first step in any pest management strategy is to seek understanding the life cycle, habits, and damage caused by the rodents that are problems for you.
Please read the Organic Standards carefully. Your certifier should provide you with a copy of the standards, and they can also be found online at www.ams.usda.gov/nop/NOP/standards/FullRegTextOnly.html.
You should also check with your certifier with any remaining questions. Of course, any material you plan to use must be included in your Organic System Plan and approved by your certifier. The standards provide several strategies to help you develop a systems-based approach to managing pests—including rodents—on your farm. Rodent management will be a continuing effort, and it is probably unrealistic to expect to fully eliminate the problem.
Predators: Some people have a great deal of success putting up nest boxes to attract owls to eat rodents. Depending on the wildlife that lives in your region, many types of predators may be able to help you, including snakes, owls, hawks, great blue herons, weasels, bobcats, coyotes, and domestic dogs and cats. More detail on design and placement is provided below.
Trapping, Habitat Reduction, and Physical Barriers: Many if not most organic farmers rely on trapping for some degree of control. Trapping can be very effective when used with persistence, skill, and appropriate type of traps (there are many kinds on the market). To be most effective, trapping must be done daily, especially at critical times in the cropping season and key seasons in the live cycle of the rodent. Many types of rodent problems may be minimized by making the farm and areas around farm buildings less hospitable to them, by removing shelter and potential food sources. Physical barriers to invasion or access to food, such as fences, wire baskets, or even trenches and irrigation.
Rodenticide Materials: National Organic Program standards for pest control (see below) list many methods of control, but only two allowed materials. Allowed pesticide materials should be used only when you have tried other methods and they are not sufficient. Any material, whether natural or synthetic, must be included in your Organic System Plan to be approved by your organic certifier. Natural materials, in general are allowed, but a few, such as arsenic and strychnine, are prohibited. Synthetic materials are generally prohibited, with a few specific exceptions that are allowed and included on the National List of allowed synthetics. For rodent control those are sulfur dioxide (smoke bombs), and Vitamin D3.
Vitamin D3 (Cholecalciferol) is listed as an allowed synthetic material for rodent pest control. Cholecalciferol-containing rodenticides produce hypercalcemia (6), making it an effective poison. Rodents generally die within two days following ingestion and do not appear to exhibit bait shyness. However, care should be used when placing this bait, particularly where dogs and young male cats are present, both of which are somewhat indiscriminate in their eating habits.
In the Generic Materials List published June 2004 by the Organic Materials Review Institute (OMRI), OMRI notes:
Vitamin D-3 cannot be the sole means of rodent control. Alternative methods for rodent control must be documented in the Organic System Plan. Growers must take precautions to prevent killing non-target animals.
There are several trade names of commercial rodenticides containing vitamin D-3 or cholecalciferol, such as: Quintox, True Grit Rampage, and Ortho Rat-B-Gone (6). Some of these rodenticides should be available from a local garden supply store or garden section of a hardware store. You will need to obtain a label from the manufacturer with a complete disclosure of the inert ingredients in the product, and ask your certifier whether these products are acceptable. Many products, although they contain an active ingredient that is allowed, also include “inert” ingredients that may or may not be acceptable for use in organic agriculture (to be allowed they must be on EPA list 4). Other sources of cholecalciferol include multivitamins containing Vitamin D, such as Viactiv (6), feed grade or dietary sources of vitamin D, and plants with calcinogenic properties (1). Cestrum diurnum (Day Jessamine) and Solanum malacoxylon plants are a source of cholecalciferol (6).
National Organic Program standards:
§ 205.206 Crop pest, weed, and disease management practice standard.
(a) The producer must use management practices to prevent crop pests, weeds, and diseases including but not limited to:
(1) Crop rotation and soil and crop nutrient management practices, as provided for in §§ 205.203 and 205.205;
(2) Sanitation measures to remove disease vectors, weed seeds, and habitat for pest organisms; and
(3) Cultural practices that enhance crop health, including selection of plant species and varieties with regard to suitability to site-specific conditions and resistance to prevalent pests, weeds, and diseases.
(b) Pest problems may be controlled through mechanical or physical methods including but not limited to:
(1) Augmentation or introduction of predators or parasites of the pest species;
(2) Development of habitat for natural enemies of pests;
(3) Nonsynthetic controls such as lures, traps, and repellents…
(e) When the practices provided for in paragraphs (a) through (d) of this section are insufficient to prevent or control crop pests, weeds, and diseases, a biological or botanical substance or a substance included on the National List of synthetic substances allowed for use in organic crop production may be applied to prevent, suppress, or control pests, weeds, or diseases: Provided, That, the conditions for using the substance are documented in the organic system plan.
§ 205.601 Synthetic substances allowed for use in organic crop production.
In accordance with restrictions specified in this section, the following synthetic substances may be used in organic crop production: Provided, that, use of such substances do not contribute to contamination of crops, soil, or water. Substances allowed by this section, except disinfectants and sanitizers in paragraph (a) and those substances in paragraphs (c), (j), (k), and (l) of this section, may only be used when the provisions set forth in Sec. 205.206(a) through (d) prove insufficient to prevent or control the target pest….(g) As rodenticides.
(1) Sulfur dioxide—underground rodent control only (smoke bombs).
(2) Vitamin D3.
§205.602 Nonsynthetic substances prohibited for use in organic crop production.
The following nonsynthetic substances may not be used in organic crop production…to treat a physiological disorder associated with calcium uptake.
(i) Tobacco dust (nicotine sulfate).
Control Options, Predators
Since chemical controls such as anti-coagulants are not preferred options, what’s needed is an increased population of predators including snakes such as gopher snakes, corn snakes, rat snakes, owls, hawks, great blue herons, weasels, bobcats, coyotes, and domestic dogs and cats.
Two of the species of rat snakes on the mainland US feed on rodents, such as mice, rats, and squirrels, are the corn snake, Elaphe guttata, and the rat snake, Elaphe obsoleta. However, please note that both species also feed on small birds, so that chicks and eggs might be at risk as well as rodents. Domestic cats are another option and will provide long-term control, although they will also prey on the songbirds on your farm.
More than 95 percent of the diet of barn owls usually consists of small mammals (mostly rodents). However, in some studies substantial bird remains have been found. According to Colvin (3) each adult barn owl may consume about one or two rodents per night; a nesting pair and their young can eat more than 1,000 rodents per year. Dietary studies from California and other states show that a barn owl consumes on average 50 to 60 grams of prey per day (0.11-0.13 pounds per day, 40-48 pounds per year). The actual species consumed depends on the species abundance and availability in the area. Barn owls will readily use man-made nest boxes. It’s clear that there is more than one way to build a barn owl box.
One model for a barn owl nesting box that is made from PVC is online at http://kaweahoaks.com/html/barn_owl_house.html.
Additional guidelines for owl housing (4):
Interior floor size (inches)
Interior height (inches)
Entrance Hole Diameter (inches)
Height to Mount Box (feet)
7 x 7
Forest clearings & edges
8 x 8
Farmland, orchards and woods
8 x 8
Boreal Forests and Bogs
14 x 14
Mature Bottomland Forest
12 x 36
6 x 7
Open Farmland, Marshes
1) National Organic Program, USDA, Organic Standards, Regulatory Text www.ams.usda.gov/nop/NOP/standards/FullRegTextOnly.html
2) An Overview of Cholecalciferol Toxicosis, The American Board of Veterinary Toxicology (ABVT), at: www.abvt.org/tow.htm
3) Colvin, B.A. Barn owls: Their secrets and habits. Illinois Audubon, No. 216 Spring. 1986.
5) Birds and Nature. Bird House Tables. Web site at: http://web.mountain.net/~shalaway/nests.html
6) Rodenticides. Source: Journal of Veterinary Medicine, archives, vol. 27, May, 1998. posted on IPM of Alaska, Solving Pest Problems Sensibly. Rocco Moschetti, P.O.Box 875006, Wasilla, Alaska 99687-5006 (907)745-SAFE (745-7233) email: email@example.com website: www.ipmofalaska.com/files/rodenticides.html
Answer: The National Organic Program Regulations state that organic producers must manage manure in a manner that does not contribute to the contamination of crops, soil, or water by plant nutrients, heavy metals, or pathogenic organisms and that optimizes recycling of nutrients. This statement implies that manure handling, storage, and application to fields are all important. Unless properly handled, manure can be a health issue for livestock and people. Accumulated manure can breed insects, generate high levels of ammonia gas, and spread diseases. The National regulations do not specify handling procedures, only that the system used cannot compromise the organic integrity.
The National Organic Program does not differentiate among livestock manure sources. However, the NOP regulations do require that livestock manure not contain any synthetic substances not included on the National List of synthetic substances allowed for use in organic crop production.
Manures from conventional systems are allowed in organic production, including manure from livestock grown in confinement and from those that have been fed GMO feeds. Manure sources containing excessive levels of pesticides, heavy metals, or other contaminants may be prohibited from use. Such contamination is most likely with manure obtained from industrial scale confinement systems, including slurry manure. Certifiers may require testing for these contaminants if there is reason to suspect a problem.
In conventional lagoon systems, stabilizing chemicals are frequently added. Be certain that the products used are an allowed stabilizer for organic management. Consult your certifier when in doubt.
Certified organic producers have strict guidelines to follow in handling and applying manure. The National Organic Program regulations require raw animal manure be incorporated into the soil not less than 120 days prior to the harvest of a product whose edible portion has direct contact with the soil surface or soil particles, and be incorporated into the soil not less than 90 days prior to harvest of a product whose edible portion does not have direct contact with the soil surface or soil particles.
Since mustards are a prime host, I will assume that brassicas, such as broccoli and cabbage are being attacked.
Harlequin bug (Murgantia histrionica), a member of the Stinkbug family
(illustration from http://ipm.ncsu.edu/AG295/html/harlequin_bug.htm)
This is a difficult pest to control due to its mobility and relatively wide host range. Ideally, several approaches based on the ecology of the stinkbug should be integrated to increase the environmental “pressure” on the pest. Harlequin bugs have evolved as crucifer-feeding specialists, so they have an affinity for plants in this family. Weedy hosts include wild mustard, shepherd's purse, peppergrass, bittercress, and watercress (1). Once the mustards become scarce, generally as a result of natural senescence, the bugs will move to squash, corn, beans, asparagus, okra, and tomatoes (1).
There are some possible weak links in its life cycle that might be taken advantage of. This pest will generally overwinter as an adult and then begin egg-laying a couple of weeks after it becomes active in the spring. In this context, it requires nitrogen for the egg-laying effort. Early-season crucifers, as they are forming seeds, are a good source of nitrogen at about the same time that the stinkbugs require nitrogen (2). It seems likely that if this nitrogen source were eliminated, harlequin bug egg production and egg viability would decrease. In California, one suggested strategy is to replace wild radish and crucifer populations that grow along roadsides and fields with native grasses. Native grasses are not attractive to stink bugs; they do not form their seeds until later in the growing season and are thus poor sources of nitrogen. Trap crops of flowering mustards have been suggested to manage harlequin bug populations. The obvious problem with this technique is finding effective and inexpensive ways to destroy the stinkbugs coming to the trap crop in a timely fashion so that they will not infest the actual brassica crop.
Another option is to increase predation of the harlequin bug. Recent research in California has found, surprisingly, that the “roly poly"—also known as the “pill bug,” due to its tendency to roll up into a pill-sized ball when disturbed—is an effective predator of harlequin bug eggs. Previously, it was thought that pill bugs fed only on decaying vegetation, but it turns out that they are nocturnal predators, climbing into plants at night in search of harlequin bug eggs and other stinkbug-family eggs. Mulching your crops with hay or woodchips may provide habitat for ground beetles and spiders that would feed on the eggs and stinkbug nymphs. Since mulching may provide overwintering sites for the stinkbug, the mulch should be removed or incorporated into the soil after the crop is harvested.
Increased predation should be accompanied by destruction of overwintering sites for the harlequin bug. Plant debris and leaf litter should be destroyed. However, it should be noted that this may be the same kind of habitat required by the predatory pill bug that feeds on stinkbug eggs. Your observations about where the harlequin stinkbugs are overwintering on your farm will guide future management efforts.
The varieties listed in the table below have some resistance to stinkbug damage and have been recommended by North Carolina State University for planting (1). Please keep in mind that the different conditions in your location relative to North Carolina may influence the plant’s development and its level of resistance.
Copenhagen Market 86, Headstart, Savoy Perfection Drumhead, Stein's Flat Dutch, and Early Jersey Wakefield
Green Glaze, Georgia (3)
Early Snowball X, Snowball Y
Red Devil, White Icicle, Cherry Belle, Champion, Red Prince, Globemaster
Row covers may be used to cover the brassicas and physically protect the plants from harlequin bug feeding, but must be placed before egg laying starts.
Liquid formulations of pyrethrum, sabadilla, and rotenone are organically acceptable botanical insecticides that are effective against the harlequin bug, but they can also harm beneficial insects.
Finally, you may wish to experiment with the particle film barrier Surround™, a processed formulation of kaolin clay. Registered for use on brassicas and most other vegetable crops, it has proved effective against leafhoppers and sharpshooters, and may have some efficacy against stinkbugs. It may act to deter feeding and egg-laying behavior once the insect has landed on the plant, as well as disguise the plant from being discovered in the first place. It is probably best for early season use, as the particle film would be difficult to wash off if applied before harvest. Contact John Mosko (see below) for additional information or material for variety trials.
101 Wood Avenue
P.O. Box 770
Iselin, NJ 08830-0770
Dufour, R. 2000. Farmscaping to enhance biological control. ATTRA publication. 39 p.
1. North Carolina State University IPM Web page. INSECT and related PESTS of VEGETABLES, Harlequin Stink Bug. http://ipm.ncsu.edu/AG295/html/harlequin_bug.htm
2. Ehler, L. 2000. Farmscape Ecology of Stinkbugs in Northern California. Entomological Society of America.
3. Harris, P., Jarratt, J.H., Killebrew, F., Byrd, Jr., J.D., and R. Snyder. Publication 2036. Mississipi State University Extension Service. http://msucares.com/pubs/publications/p2036.htm