Brassica spp., family Cruciferae
Three species of mustard are grown commercially for their seed from which an excellent oil and the condiment, table mustard, is produced. They are (1) B. hirta Moench (B. alba (L.) Rabenh.), white or yellow mustard; (2) B. juncea Coss, Indian (oriental and brown types), Chinese, leaf, and trowse mustards and rai; and (3) B. nigra (L.) Koch, black mustard. (Also see "Cole Crops," p. 164, and "Rape," p. 315.)
Mustard is a minor crop in the United States, but in 1941, 124,000 acres were grown in Montana, with small amounts in North Dakota, Oregon, and Washington (Straw 1956). The crop in Canada is expanding with about 200,000 acres in 1970 versus 4 million acres of rape (Downey et al. 1970), and its importance is likely to increase in the United States. Black mustard is not grown in Canada, and the major acreage is devoted to yellow mustard.
Yields of 1,000 to 1,500 pounds of mustard seed per acre are obtained in Canada (Downey et al. 1970), which is more than the U.S. production of 468 to 714 pounds reported by Shaw (1956), the 451 to 524 pounds reported by Robinson (1964), or the 500 to 1,000 pounds of brown or 250 to 1,000 pounds of yellow mustard reported by Martin and Leonard (1949*).
Mustard and rape production is similar in many ways, however, each crop is a serious contaminant of the other. For that reason, the two crops should not be grown on the same farm and preferably not in the same area.
Young mustard plants are quite similar to many other Brassica plants; however, differences soon begin to appear. The rosette of broad basal succulent leaves, about 1 foot high, produces the upright flowering stem that reaches 1 1/2 to 10 feet and terminates with the inflorescence. The upper leaves are much smaller than the lower ones and may be deeply lobed or entire and more or less oval. The growing season is similar to that of wheat or slightly shorter. Like rape, mustard is a cool season crop, but is more drought tolerant than rape. The seeds do not shatter, so the seed crop can be harvested (combined) without undue loss. Mustard is usually seeded at the rate of 4 to 10 lb/acre, depending upon the type and cultivar (Downey et al. 1970).
When mustard and rape were compared, Downey et al. (1970) stated "In comparison to 'Echo' rapeseed, yellow mustard is a few days later in maturing, has yellow seed that is about twice the size, and shows more vigor in the seedling stage. Yellow mustard begins flowering at the same time but continues to flower longer. It is similar to 'Echo' in height, is more resistant to shattering, but slightly lower in yield." In general, the mustards are slightly taller and also have thinner leaves and smaller flowers than rape. B. nigra may grow to 10 feet or more in height, with four-sided pods less than 1 inch long. B. hirta and B. juncea grow only to 2 to 4 feet, with B. hirta having pods 3/4 inch to 1 1/2 inches long with strong constrictions between the seeds, whereas pods of B. juncea are longest, 1 1/2 to 2 1/2 inches.
The mustard inflorescence is an aggregate of yellow florets at the apex of the raceme, that give a field a deep golden appearance when fully open. The structure of the flower, as given under "Cole Crops," applies equally to the mustard flower. Free (1970*) indicated that the two outer nectaries were somewhat functional but Nieuwhof (1969) stated that they were inactive. Mustard is an excellent source of nectar and pollen for honey bees (Pellett 1947*).
According to Howard et al. (1915), the floret opens between 9 a.m. and noon, and remains open for 3 days. Usually, the stigma projects about 2 mm beyond the petals the afternoon preceding opening of the flower and is immediately receptive. Soon afterwards, however, the corolla begins to grow and reingulfs the stigma. Then the stamens lengthen so that the anthers are level with the stigma, but when the corolla opens, they turn half around. At this period, nectar secretion by the inner nectaries begins. Just before the flower closes, the anthers turn to their former position, and, if any degree of self-fertility exists, selfing can result.
Muller (1883*) stated that the position of the anthers in relation to the nectaries and stigma makes cross-fertilization likely but by no means inevitable on the visit of pollinating insects. The flower is so constructed that pollen from another flower is likely to be transported to it before its own pollen comes in contact with the stigma. Some of the self-pollen may contact the stigma without the aid of insects, but this contact can be abetted by the bees' visit to the flower. Sampson (1957) showed that compatibility varies with species, cultivar, and even the age of the plant.
Free and Spencer-Booth (1963) found that bees more than doubled seed production of B. alba. In B. juncea, production was increased only 14 percent, an amount that was not statistically significant in their test, but could be of great significance to the grower. Pritsch (1965) also obtained significantly greater yields of white mustard in cages with bees than in cages where bees were excluded. Olsson (1952) obtained a set of 64.7 percent of the flowers, with 2.46 seeds per pod, and 1.75 g per pod with bees excluded, but with bees present these values were increased to 95.3, 4.08, and 2.69, respectively, more than doubling total production. Koutensky (1959) also showed that the seed yield of white mustard was increased 66 percent by honey bee pollination. Howard et al. (1916) indicated that B. juncea was self-fertile but abetted by wind, Downey et al. (1970) stated that oriental and brown mustards (B. juncea) are generally self-pollinated, but yellow mustard (B. hirta) is a cross-pollinated crop. They further stated that wind and bees are both effective in pollination. Free (1970*), citing Akhter (1932) and Olsson (1960), indicated that B. nigra is largely self-sterile.
The above references indicate that yellow mustard is immensely benefited by bee pollination, but the value to oriental or brown mustard is minor, although the actual effect of supplemental pollination has not been too well tested.
Olsson (1955) found pollen on glass slides exposed 1, 5, 20, and 40 m from fields of rape, turnip rape, and white mustard and he deduced that wind was important in the pollination of these crops. Howard et al. (1916) also believed that wind contributed to pollination. However, mustard is basically an insect-pollinated type of crop, with ample pollen and nectar to attract pollinating insects. Honey bees in particular are attracted to it, and they were shown by Free and Spencer-Booth (1963) to be of great benefit to B. hirta and possibly to B. juncea. The data indicate that repeated visits would be beneficial, thus an ample supply of bees should be present. The number of bees per unit of mustard flowers has not been determined. The flowers are highly attractive to bees for both nectar and pollen so there is no problem in getting visitation if sufficient bees are in the area and the weather permits floral visitation.
Pollination Recommendations and Practices:
No colony recommendations have been made for mustard. Downey et al. (1970) stated, "It has not been found necessary to supply honey bees to produce good seed yields." How maximum production is obtained is not explained, because they indicated that most of the 200,000 acres devoted to mustard seed production is of B. hirta, and the data indicate that production of B. hirta provided with bees is double that where no bees are provided. This indicates that the provision of bee colonies to yellow mustard fields in adequate numbers, probably one to two colonies per acre, should be encouraged.
AKHTER, A. R.
1932. STUDIES IN INDIAN BRASSICAE. I. STERILITY AND SELECTIVE POLLEN TUBE GROWTH. Indian Jour. Agr. Sci. 2: 280-292.
DOWNEY, R. K., PAWLOWSKI, S. H., and McANSH, J.
1970. RAPESEED - CANADA'S "CINDERELLA" CROP. Ed 2. Rapeseed Assoc. of Canada Pub. 8, 40 pp.
FREE. J. B., and SPENCER-BOOTH, Y.
1963. THE POLLINATION OF MUSTARD BY HONEYBEES. Jour. Apic. Res. 2: 69 - 70.
HOWARD. A., HOWARD G. L. C., and KAHN. A. R.
1915. STUDIES IN INDIAN OILSEEDS. I. SAFFLOWER AND MUSTARD. Indian Dept. Agr. Mem. Bot. Ser. 7: 237-272.
HOWARD, G. L C., and KHAN, A. R.
1916. STUDIES IN INDIAN OIL SEEDS. I. SAFFLOWER AND MUSTARD. Indian Dept. Agr. Mem. Bot. Ser. 7: 214-272.
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1969. COLE CROPS. 353 pp. Leonard Hill, London.
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______ 1955. [WIND POLLINATION OF CRUCIFEROUS OIL PLANTS.] Sverig. Utsadesforen. Tidskr. 65(6): 418-422. [In Swedish, English summary.]
______ 1960. SELF-INCOMPATIBILITY AND OUTCROSSING IN RAPE AND WHITE MUSTARD. Hereditas 46: 241 252.
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ROBINSON, R. G.
1964. MUSTARD AND RAPE OILSEED CROPS FOR MINNESOTA. Minn. Agr. Ext. Serv. Bul. 311, 12 pp.
SAMPSON, D. R.
1957. THE GENETICS OF SELF- AND CROSS-INCOMPATIBILITY IN BRASSICA OLERACEA. Genetics 42: 252 - 263.
SHAW A. F.
1956. MUSTARD SEED PRODUCTION. Mont. Agr. Ext. Serv. Cir. 261; 6 pp.