Flowers are in a branching panicle with female (pistillate) flowers at the top and male (staminate) flowers on the lower portion. Cross pollination usually occurs since female flowers emerge first and become receptive and are pollinated before male flowers shed pollen on the same panicle. Sometimes the transition florets, which are located between the pistillate and staminate florets on the panicle, have both stigmas and anthers (pollen), and can therefore be self-pollinated. Two weeks after fertilization the wild rice seeds are visible, and after four weeks, it is ready for harvest. This seed is a caryopsis that is similar to the grain of cereals. The caryopsis has an impermeable pericarp, large endosperm, and small embryo. The grains with the palea and lemma (hulls) removed, range from 8 to 16 mm in length, and from 1.5 to 4.5 mm in diameter (Fig. 4). Immature seeds are green, but turn a purple-black color as they reach maturity. Seeds on any tiller will mature at different times, and on secondary tillers they mature later than on main tillers.
Seeds of Z. palustris will not germinate for at least three months after reaching maturity, even if environmental conditions are satisfactory for growth. An afterripening period is required in water at freezing or near-freezing temperatures (3°C) before the embryo breaks dormancy and develops into a new seedling. This seed dormancy is caused by the impermeable pericarp that is covered by a layer of wax, and by an imbalance of endogenous chemical growth promoters and inhibitors (Albrecht et al. 1979). In the spring, seeds will start to germinate when the water temperature reaches about 7°C. Freshly harvested seeds can be made to germinate by carefully scraping off the pericarp directly above the embryo. Nondormancy has been found in seeds from plants of Z. aquatica that grows in Florida.
Businessmen and botanists have thought about cultivating this plant for over 100 years (Steeves 1952). Early European explorers collected seed for planting in Europe but these failed probably because the seed was not handled properly to remain viable. In 1828, Timothy Flint in Geography and History wondered why so little attention has been paid to wild rice. In 1852, Joseph Bowron suggested wild rice be seeded for agricultural purposes. In 1853, Oliver Kelly, founder of the National Grange, made the same proposal. Mechanical harvesting of private lands in Canada started in 1917, by H.B. Williams and Z. Durand (Trevor 1939).
Since about 1950, wild rice has been in the process of becoming a domesticated crop in the United States and is now being grown commercially in both the United States and Canada (Oelke et al. 1982; Stevenson 1988). Prior to that time, natural stands were the only source of the grain, and supplies were limited and varied greatly from year to year. With the advent and growth of commercial production, supplies of wild rice have increased tremendously over the last 25 years. Natural stands continue to be harvested, but the proportion of total supplies derived from natural stands has steadily declined. In some areas, including the entire state of Minnesota, natural stands of wild rice, by law, must be harvested only by traditional canoe-and-flail method, whereas in some parts of Canada, mechanized harvest is permitted. Included in Table 1 are annual harvest estimates from natural stands in Minnesota since 1963. Of all the wild rice harvested by hand, Minnesota is likely to account for more than half in any given year.
In Canada, commercial production of wild rice takes place predominantly in lakes leased from the various provincial governments (Winchell and Dahl 1984). Lease provisions vary by province, but generally lease holders are permitted to seed the lakes and, in some cases, to control water levels, and are granted exclusive harvesting rights. Much of the wild rice acreage in these leased lakes is harvested with the use of airboats (Stevenson 1988). Shown in Table 1 are annual harvest estimates from lakes and rivers in four Canadian provinces since 1963.
In the United States, wild rice is being produced commercially as a "domesticated" field crop in diked, flooded fields. Minnesota and California account for most of the hectarage (8,000 and 4,000 ha, respectively, in 1992) with additional amounts in Idaho, Wisconsin, and Oregon. Table 2 shows production totals from cultivated fields in Minnesota and California since 1968.
Growing wild rice as a field crop was first attempted near Merrifield, Minnesota in 1950-1952 (Oelke et al. 1984). James and Gerald Godward diked a 0.5 ha area, planted it with seed collected from a nearby lake, and flooded the field. The field was drained before harvest and the crop was harvested by hand. An additional 16 ha were planted by them in 1953 and harvested with a small pull-type combine. They had good crops the first few years, but leaf blight (Bipolaris oryzae B. de Haan) caused serious losses thereafter. However, they continued their pioneering efforts, and today one of their sons has nearly 1,000 acres in wild rice production.
Initially, the only seed available for planting in fields was of shattering types found in natural stands. These early fields were harvested several times over a 2-to 3-week grain-ripening period with specially designed, multiple-pass harvesters (Fig. 5). In 1963, Dr. Paul Yagyu and Mr. Erwin Brooks with the University of Minnesota, Department of Agronomy and Plant Genetics, discovered plants in a grower's field that retained their seed longer than the rest of the plants (Oelke et al. 1984). From these few plants, they and other breeders developed cultivars with more resistance to shattering than types growing in lakes and rivers. Today, most of the wild rice being grown in fields are more shattering resistant. Yields of unprocessed grain from shattering types grown in fields typically ranged from 168 to 224 kg/ha, whereas, with shattering resistant cultivars, yields have been reported as high as 1,680 kg/ha in Minnesota and twice that amount in California.
The development of more shattering resistant cultivars of wild rice was largely responsible for a tremendous expansion in field production that occurred in the late 1960s and early 1970s. Practically all the expansion at that time was taking place in Minnesota where area increased from 354 ha in 1968 to 7,090 ha in 1973 (Oelke et al. 1982). The finding of improved shattering resistance was the development that eventually made possible the shift to more efficient harvest with grain combines (Fig. 6). The improved harvest efficiency from the use of combines, together with greater harvested yields from shattering resistant cultivars, were major contributing factors to expanded field production at that time.
Other factors that were important in the development of wild rice as a field crop were: the contracting of production by Uncle Bens, Inc., and the formation of Manomin Development Corporation for development of seed, growing, and marketing of wild rice in 1967; the formation of a Wild Rice Growers Association and the initiation of a research program on processing at the University of Wisconsin-Madison in 1970; and the initiation of a research program at the University of Minnesota on breeding, production, diseases, insects, soil fertility, machinery, and processing in 1972. In 1974, a Minnesota Paddy and Wild Rice Research and Promotion Council was formed after growers voted to contribute a specified fee for each pound of processed grain produced for promotion and research of the crop. In the early 1970s, growing wild rice as a field crop began in California and by 1987, the added production had a significant impact on supply and price. In 1982, an International Wild Rice Association was formed which now includes all producers, processors and marketers in the United States and Canada.
Marketing and processing of wild rice was significantly aided by the formation of two cooperatives in Minnesota (Winchell and Dahl 1984). In 1971, the first successful cooperative was United Wild Rice, Inc. (United). They constructed facilities and staffed the program with a professional manager and sales force. A second cooperative, Minnesota Wild Rice Growers (MRG) was formed in 1974. In 1983, a third cooperative was organized under the name of the Independent Wild Rice Producers Association. Later in 1987, a marketing and product development company, New Frontier Foods, Inc. was formed by some growers. In 1986, Busch Agricultural Resources purchased the processing facilities and marketing operations from United Wild Rice thus involving another large marketer in the industry. The marketing of the cultivated crop was significantly aided by the long-time harvest and marketing of the grain from natural stands. The name of the product was already established in the gourmet markets, thus the cultivated crop could exploit the gourmet nature of the grain.
Even though wild rice is grown now on hectarage in several states it is continuing to undergo domestication in that wild rice still possesses several traits of a wild species such as some seed shattering, seed dormancy, tiller asynchrony, and variable seed size (Hayes et al. 1989). However, these traits are under genetic control and given the heritability of these traits, deliberate selection should accelerate the domestication process.
The crop is grown similarly to rice (Oryza), thus relatively flat areas are needed where a flood can be maintained for most of the season (Fig. 7). It will grow well on organic or inorganic soils if the proper nutrients are applied. Since the plant is relatively tall, its nitrogen requirements are lower than for rice. In addition, it will grow well in cooler and deeper water than rice, thus requiring fewer weed control chemicals compared to rice.
Wild rice seed needs to be stored for 90 days in cold (3°C) water before dormancy is released. Seed storage is an added cost in the Sacramento Valley of California compared to Minnesota. Wild rice seed loses viability, especially after dormancy release, when it is allowed to dry below 25% moisture content. Dormant seed, however, can withstand drying below 25% moisture but needs to be stored in cold (3°C) water for 90 days to release dormancy (Oelke and McClellan 1992). In contrast to rice seed, wild rice seed when planted 5 to 8 cm into the soil before flooding can still grow while rice seed cannot when covered for more than a few days by both soil and water. In Minnesota, new fields are seeded with 45 kg/ha of seed (35% moisture) while in California a seeding rate of 112 kg/ha is common. A higher seeding rate is used in California because plants don't tiller as much as in Minnesota and also a higher plant population can be utilized since no leaf diseases are prevalent.
In Minnesota and Wisconsin fields are prepared, fertilized, and seeded in the fall and flooded to a depth of about 30 cm in the spring. In California, these operations are done in the spring except in some of the higher elevations where production practices are similar to those in Minnesota.
In Minnesota, once a field is seeded to wild rice it will reseed itself due to seed shattering even when planted to cultivars with some shattering resistance. Thus, fields are generally kept in production for 3 to 4 years. It is also difficult to change a field to a new cultivar due to seed dormancy, causing volunteers the following year. Cultivars without seed dormancy are needed to allow more rapid adoption of new, improved cultivars. The plant density the second and following years is also too high making it necessary to reduce the plant population by airboats equipped with a series of V-shaped knives set 15 to 20 cm apart on a toolbar attached to the rear of the boat. The boat travels at a speed of 55 km/h with the knives riding on the soil surface, and removing about 70% of the plants. The plant density desired is 40 plants/m2.
In Minnesota and California, fields are drained about 3 weeks before harvest with combines. Combines are often adapted with half or full tracks for ease of harvesting in moist soils. The grain is harvested at 30% moisture since seed shattering occurs if allowed to dry more on the plant. The moist grain is immediately transported to processing plants and not dried or stored on the farm like other cereals. At the processing plant the grain is cured, parched, hulled, and graded (Fig. 8).
Brown spot (formerly called Helminthosporium brown spot) is the most serious disease affecting wild rice that is grown in fields in Minnesota but, is not a problem in California. This disease is caused by Bipolaris oryzae Luttrell (Helminthosporium oryzae B. de Haan) and B. sorokiniana Luttrell (H. sativum P.K. and B.). These fungi are considered to cause brown spot since both are found on infected plants and cause similar symptoms. Every cultivar of wild rice, at each stage of development, is susceptible to brown spot. This disease is most severe when day temperatures range from 25° to 35°C and nights are 20°C or warmer. High relative humidity (greater than 89%), and the continuous presence of free water on leaf surfaces for 11 to 16 h, also favor infection. All parts of the plant are susceptible to infection. The brown, oval leaf spots usually have yellow margins and are about the size of sesame seeds. These spots are uniform and evenly distributed over the leaf surface. Severe infections cause weakened and broken stems, damaged florets, and a reduced quantity and quality of grain. Yield reductions can vary from insignificant to 100%. Sanitation and a fungicide are needed for control.
Stem rot is the second most common disease in field-grown wild rice. Two fungi, a Sclerotium sp. and Helminthosporium sigmoidium Cav., may cause this disease. These fungi produce dark structures called sclerotia in culms, leaf sheaths, and stems. Small, oval, purple lesions develop initially on stems or leaves at the water surface. Extensive lodging may result after the fields are drained prior to harvest, since the infected stems become necrotic, dry, and brittle. Control of stem rot is achieved most effectively by appropriate sanitation and cultural practices. Plant residue must be removed or tilled into the soil, only clean seed should be used, and resistant crops or fallow should be in the rotation. There is no fungicide available for effective control.
Stem smut is caused by the fungus Entyloma lineatum (Cke.) Davis. Economic losses from this disease have not been a problem in cultivated fields.
Ergot is rarely found in cultivated fields of Minnesota, but can be a serious problem in natural stands. This disease is caused by the fungus Claviceps zizaniae Fyles, which is a different species than the one causing ergot in cereal grains. Wind-borne ascospores infect flowers and hard, dark sclerotia eventually develop in place of the grain. No specific control is recommended, but poisonous ergot bodies should be removed from harvested grain by flotation, or by screening.
Bacterial leaf streak and wheat-streak mosaic virus have been found in cultivated wild rice in Minnesota. Bacterial leaf streak is caused by Pseudomonas syringae. The wheat streak mosaic virus-wild rice is the only one known to infect wild rice. Economic losses for grain yield, if any by these diseases, have not been determined. No control measures are known.
The rice worm (Apamea apamiformis Guenee), which s the larval stage of the noctuid moth, is the most serious insect pest of wild rice in the Upper Midwest but not a problem in California. Significant yield losses have been caused by this insect. Its life cycle is coordinated closely with the growth and development of wild rice. Adult moths begin to emerge at about the same time as flowering begins in wild rice during late June or early July. Nectar from milkweed flowers serves as the primary food source for adult moths through August. Eggs are deposited in wild rice flowers over a period of 4 to 6 weeks. Larvae hatch and develop through several instars or stages, and feed as they grow. Yield potential is reduced by the initial feeding activity on the glumes of the spikelet and subsequent feeding on kernels. Rice worms bore into stems of wild rice or migrate to plants that border the production area as their growth and development nears completion. Rice worms overwinter inside the stems in the seventh instar. After a final molt and some additional feeding in the spring, the larvae usually pupate in early June, and develop into the adult moth. Research in Minnesota found that one larva per plant reduces yield by 10%. Control of the rice worm has been effective with several insecticides; yet only malathion at one pound of active ingredient per acre (1.1 kg/ha) is approved for use in Minnesota.
A number of midges use the flooded paddies for larval development. Eggs are laid in the moist soil and hatch when the fields are flooded. One of the midges, Cricotopus spp., has caused severe damage to first-year fields in Minnesota and California. The mosquito-like adults are so small that most growers will not see them. Algal growth is associated with paddies showing high midge numbers. A slow emergence of seedlings results in greater damage by midges since it allows more time for feeding activity. The larvae feed on leaf edges and cause frayed leaf edges with subsequent curling of leaves. The leaf curling and webbing that midges produce will interfere with seedling emergence above the water. As a result, the damaged seedlings fail to reach the floating-leaf stage and the stand is thinned severely. Midge control with malathion is often necessary in first-year fields. In the following years control is not usually necessary since there is no economic loss. This is not the result of a lack of midges, which actually increase in number, but due to higher plant numbers so the damage goes unnoticed.
Rice stalk borers (Chilo plejadellus Zincken), rice water weevils (Lissorhoptrus spp.), rice leafminer (Hydrellia spp.), rice stem maggot (Eribolus longulus Loew), and other insects will feed on wild rice plants. Research in Minnesota did not reveal any economic injury from these insects.
Crayfish (Orconectes virilis Hagen) are carried into paddies by flood waters where they forage and may cut back the seedlings. Once crayfish are established in a field, they persist and can increase in number. They survive in production fields by burrowing into moist soil between periods of paddy flooding. Severe stand reductions have occurred in some fields in Minnesota. No chemicals are cleared for their control.
Blackbirds are a major pest in both Minnesota and California. These birds use the paddy dikes as nesting sites and are present in large numbers in the growing areas. Birds begin feeding on wild rice when the kernels are in the milk stage. Control measures should start when blackbirds are first observed in the area.
Wild rice fields are also ideal sites for resting, foraging, nesting, and raising broods of migratory and resident water birds. Four species of ducks (mallard, pintail, blue-wing teal, and green-wing teal) and more than 35 species of shorebirds and wading birds inhabit wild rice paddies. Economic damage from waterfowl is rarely observed. Paddies are excellent areas for duck production.
Raccoon, mink, and skunk search for food on the dikes and in ditches. Deer and moose occasionally cause some damage in the fields, but it usually has no economic importance. Muskrats can cause problems by feeding on seedlings and mature plants and by burrowing holes in the sides of dikes. However, since muskrats are not permanent inhabitants due to the annual drainage of the paddies for he harvest, they do not pose a threat to the dikes.
The common broadleaf water weeds of the Upper Midwest are a more serious problem than aquatic grassy weeds. Common waterplantain (Alisma trivale Pursh), an aquatic perennial weed, is the most troublesome weed in wild rice fields. Early control of waterplantain is critical since competition with wild rice is greatest after 8 weeks of growth. First-year seedlings of waterplantain are usually too small and late in appearance to compete with wild rice. Water management is the major control measure.
'K2' has a medium height, early to medium maturity, and medium to high yield. Developed by Kosbau Brothers in 1972.
'M3' has a medium height, medium to late maturity, high yield, and variable plant and panicle type. Developed by Manomin Development Co. in 1974.
'Meter' has a shorter height, very early maturity, low to medium yield, and large seed size. Reduced foliage in the canopy compared to other varieties. Released by the Minnesota Agricultural Experiment Station in 1985.
'Netum' has a medium height, early maturity, and low to medium yield. Released by the Minnesota Agricultural Experiment Station in 1978.
'Voyager' has a short to medium height, early maturity, and medium to high yield. Should equal or exceed K2 in yield and mature a few days earlier. Released by the Minnesota Agricultural Experiment Station in 1983.
In California, cultivars developed by NorCal Seeds are the predominant ones grown.
Fig. 1. The traditional hulling method "jigging" of dried hand harvested grain from lakes.
|Fig. 2. Distribution of wild rice in North America. Adapted from USDA, Technical Bulletin 634.|
|Fig. 3. Z. palustris plant at flowering.|
|Fig. 4. Z. palustris grains with (top) and without lemma and palea (bottom).|
Fig. 5. Multiple pass harvester used to harvest shattering types.
Fig. 6. Harvesting cultivars which have same shattering resistance.
Fig. 7. Flooded wild rice fields in northern Minnesota.
Fig. 8. Equipment used to turn and water wild rice grain daily during curing at the processing plant.