SUNFLOWER
Helianthus annuus L., family CompositaeThere are two types of annual sunflower, oilseed and nonoil. Oilseed sunflower is a source of high-quality seed oil, which is used in cooking, salads, paints, and as an industrial lubricant. Seed from the nonoil type is used as a bird feed or roasted and marketed as a confectionery product. Until 1972, most of the sunflower acreage in the United States was of the nonoil type.
Minnesota and North Dakota are the major producing States. The crop is being tried in many other States to a limited extent. The oil from cultivars grown in Minnesota contains more of the desirable linoleic acid than the oil from the same cultivars grown in Central or Southern United States.
Other major sunflower producing countries are Russia (11 to 12 million acres), Argentina (3 million acres), and Romania (11/2 million acres). There were 850,000 acres in the United States in 1972 (Robinson 1973).
Plant:
The sunflower is a widely adapted plant. It will grow in the arid Southwest, yet at some stages of growth it will tolerate light frosts. It is native to North America and is the only important annual crop to evolve and be domesticated within the confines of the United states. Little heed was given it, however, until it was transported to Europe and returned, via Canada, as an important oilseed crop. Not until 1947 did oilseed production develop in the United States, in Minnesota. Most of our cultivars originated in Russia, or they have been developed from Russian cultivars. However, Kinman and Earle (1964) showed that some of the best American cultivars outyielded the best Russian cultivars in tests with comparative linoleic acid values.
When handled as a row crop, most growers prefer row widths of 20 to 36 inches with 15,000 to 30,000 plants per acre. The exact plant population most desirable depends upon the type grown, rainfall, temperature, and soil fertility. Average production is about 1,100 pounds seed per acre (Anonymous 1969), although much higher production has been reported by individuals (Killinger 1968, Noetzel43, Trotter and Giran 1970, Weibel etal. 1950).
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43 NOETZEL, D. M. 1968 INSECT POLLINATION RESULTS ON SUNFLOWERS. Pp. 108 - 112. Dept. Ent., N. Dak. State Univ., Fargo. 1968. [Mimeographed.]Inflorescence:
The sunflower stalk has a main or primary flower head and may have one to several secondary heads (fig. 179). All commercial cultivars are composed of almost 100 percent single-headed plants. The main head may have from 1,000 to 4,000 individual florets, depending upon the cultivar and size of the head. A secondary head may have from 500 to 1,500 florets. The outer or ray florets with the showy yellow petals are sterile, having neither stamens nor pistil (fig. 180). The less conspicuous florets making up most of the head are hermaphrodite, but protandrous, and many are self-incompatible. They are normally open 2 or more days. The first day, the anthers release their pollen in the anther tube, which is partly exserted from the corolla. The pollen is collected freely by bees, along with the nectar at the flower base. The second day, the stigma pushes up through any pollen mass remaining, then its two lobes open outward, receptive to pollen but out of reach of its own pollen (Putt 1940).
The opening of all the florets of a single head takes 5 to 10 days. If pollination occurs, the floret withers shortly; otherwise it may "wait" as long as 2 weeks for fertilization. Seed setting on such florets, however, is greatly reduced even with cross-pollination (Avetisyan 1965, pp. 209- 248). A typical head in bloom will have dried florets toward the outside, then a ring of florets with receptive stigmas, a ring of florets shedding pollen, and, finally, unopened florets toward the center. Radaeva (1954) stated that within 3 days after the first flower head begins to open 83 percent of the remaining heads also begin to open.
Both the pollen and the nectar of sunflower are quite attractive to bees throughout the day (Bitkolov 1961, Free 1964). Nectar is secreted at the base of the floret, primarily during the pollen-producing stage of flowering but to some degree while the stigmas are receptive. Extrafloral nectaries in the bracts and on the upper leaves of the plant are sometimes visited by honey bees, particularly in the afternoon (Free 1964).
Sunflowers are considered by beekeepers to be a fair source of pleasant-flavored, yellow-colored honey (Anonymous 1969, Burmistrov 1965). Furgala (1954a) reported that a colony on scales gained 104 pounds in 15 days while on sunflowers, which he considered an indication that the area was underpopulated for adequate sunflower pollination. Baculinschi (1957) calculated the nectar crop at about 20 lb/acre for the entire flowering period. This is roughly equal to nectar production of cantaloupe, as calculated by McGregor and Todd (1952*). Guynn and Jaycox (1973) reported a yield of 80 pounds of honey per colony when 15 colonies were placed at the center of a 45-acre field of sunflowers.
[gfx] FIGURE 179. - Sunflower head, showing the brilliant yellow but sterile ray flowers around the outside, and the fertile florets in different stages of development in the center.
FIGURE 180. - Longitudinal section of sunflower head, x 1/2, with individual florets. A, Ray floret, x 5; B, disk florets in different stages of developement, x 5.
Pollination Requirements:
If pollen from a floret is transferred to the receptive stigma of another flower on the same head and the flowers are self-compatible, seed will set. However, most cultivars are self-incompatible (Free and Simpson 1964), in which case the pollen must come from another plant. When selfing (within the head) occurs, seed setting is usually low (Barrett 1954, Cardon 1922, Kalton 1951), the seeds are undersized, and the oil content and germination are reduced. Selfed seed also sprout more slowly, and production from them is lower than from plants derived from crossed seed. Putt and Heiser (1966) described two types of genetic male sterility in sunflowers.
Putt (1966) observed strong hybrid vigor in sunflowers; 2,291 lb/acre with 33 percent oil in his crosses as compared to 1,156 lb/acre of seed with oil content of 30 percent in his inbreds. Some "hybrid" seed has been produced by use of either a self-incompatible line or one producing little viable pollen, which is pollinated by a line that is a copious producer of viable pollen (Robinson et al. 1961). Genetic male sterility is also used to produce commercial F1 hybrid seed, but full exploitation of the hybrid vigor possible in sunflower will come when cytoplasmic male sterile female parents can be crossed with male parents that will restore fertility to this hybrid (Kinman 1970).
Sources of cytoplasmic male sterility (Leclercq 1970) and fertility restoration (Kinman 1970) have recently been discovered, and preliminary tests indicate that the yields of the Fl hybrids produced by this method are comparable to yields of the best hybrids produced by other means.
When Pritsch (1965) compared seed set in cages with and without bees, his results were inconclusive. However, others have shown a strong beneficial effect from insect pollination. Sanduleac (1960) compared seed production from four pollination treatments: (1) Isolated under gauze; (2) isolated under gauze and hand pollinated four times; (3) open to insect pollination; and (4) open to insect pollination and hand pollinated four times. His production was always greatest on open plots, with no increase derived from the extra hand pollination. His pollinator population, however, was not indicated. Avetisyan (1965) said that for best seed production each floret should be visited 8 to 10 times. Habura (1957) also obtained a higher set of seed from cross-pollinated flowers than from selfed flowers. Pinthus (1959) stated that a higher percentage of selfed seed was produced under lower temperatures at flowering. He showed that although 50 to 60 percent of the seed of bagged flowers developed between October 15 and November 30, only 0.4 to 5.0 percent developed between June 10 and September 25, during the normal period of seed production. Luttso (1956) also compared set of seed on 10 heads exposed to three treatments. His results in grams of seed produced were: Caged without bees, 315 g; exposed to bees, 995 g; and exposed to bees in addition to supplemental pollination of the heads with a soft mitten, 1,000 g. He showed that the labor of 1 man-day per acre was about equal to the bee pollination services. Schelotto and Pereyras (1971) He showed that sunflower seed yield in Argentina was increased five to six times, and the oil content of the seed was increased 25 percent in plots exposed to honey bee colonies as compared to plots isolated from insects during flowering.
Furgala (1970) reviewed the effects of insect pollination on seed production and urged that more research be conducted. The evidence is strong, however, that insect pollination is needed for commercial production of sunflower seed. Posey (1969) compiled 133 pages of literature citations on sunflowers from January 1960 to June 1967. Only 24 of these references concerned sunflower pollination, and only two of the 24 were published in the English language. This indicates the lack of interest in the pollination of this crop outside Russia.
Pollinators:
Honey bees are the primary pollinating agents of sunflowers almost wherever they are grown (Cardon 1922, Cirnu 1960, Fomina 1961, Glukhov 1955, Overseas Food Corporation 1950, Pritsch 1965, Radaeva 1954). If there is a shortage of honey bees in the sunflower fields, a small seed crop is harvested.
In some localities, bumble bees and sundry other wild bees visit sunflowers (Cockerell 1914). Arnason (1966) indicated that in many instances these bees are adequate, but all other researchers have shown that the bulk of the pollination in commercial sunflower production is by honey bees. Radaeva (1954) showed that honey bees are much more effective than wild insects. The evidence indicates that if sufficient flower heads are available for bees to collect honey surplus to the needs of the colony, the ratio of bees per flower is inadequate for maximum seed production.
The exact number of bees needed for maximum pollination has not been determined. Measurements of bee activity have included bees per flower head, bees per unit of row, bees per acre, and colonies per acre. These have been correlated to some degree with seed production. For example, Noetzel44 placed one colony per acre at the ends of different sunflower fields in North Dakota. He counted the bees per head and obtained seed production data at different distances from the apiary. He obtained an overall increase of 20 percent due to the bees alone, but beyond 400 feet from the apiaries he got no measurable increase in yield.
Noetzel's production ranged from 1,350 to 4,962 lb/acre within 50 feet of the apiary as compared to the range of from 734 to 2,249 lb/acre at 1,300 feet from the apiary. Robinson et al. (1961) harvested 1,231 to 1,653 lb/acre from their plots in Minnesota but gave no indication of the pollinator population in the plots. Bees were not provided to the plots, but apparently they were abundant in the vicinity. Furgala (1954b) reported that three to five colonies per acre significantly increased yield. Furgala (1954a) reported that a field produced 1,300 lb/acre near the apiary, 900 lb/acre at a distance of 400 feet, and 800 lb/acre at 1,000 feet, whereas the field not supplied with bees produced about 700 lb/acre at all sites.
Alex (1957) obtained only 311 pounds per acre in cages without bees, 602 pounds from cages with honey bees present, and 931 pounds from open plots freely visited by bees, differences that were significant at the 5 percent level of confidence. All were relatively low yields, partly due to drought conditions. Blackman (1951) stated that a shortage of bees can be a limiting factor in maximum seed production. Glukhov (1955) showed the following correlation between honey bee visits and production of seed:
[gfx] fix table:
Number of honey bee kilograms of seed visits per floret from a million florets 1.0 53 1.4 76 3.4 133 6.0 210 10.0 210
This gives support to the recommendation of Avetisyan (1965) that each floret should receive 8 to 10 bee visits.
Kushnir (1960) obtained 1,696 g/8 m2 plot at 400 m from the apiary, 1,373 g at 2,000 m, and 266 g from isolated plots. He had shown earlier, however, that weight of seed was not the entire story. For example, he (Kushnir 1957) showed that 100 bee-pollinated seed weighed 9.27 g and had 86.9 percent germination, whereas 100 selfed seed weighed only 2.98 g with only 9.2 percent germination. In shape, the selfed heads were uneven. Later, he (Kushnir 1958) found in another test that the kernels from 100 seeds from bee-pollinated flowers weighed 5.7 g, whereas kernels from 100 selfed seed weighed only 0.5 g.
Kurennoi (1957) likewise found that seed production 400 m from the apiary with 5.1 bees per flower was 1.81 tons /ha (1,465 lb/acre); at 2,000 m, production with 2.9 bees per flower was 1.77 tons/ha (1,384 lb/acre).
Kovalev and Ul'yanichev (1961) studied the effect of bee pollination on 12,000 ha of sunflower. They found that better pollination accounted for an overall 14.5 percent increase in yield of seed.
Cirnu (1960) stated that bee pollination increased production of seed 10 to 30 percent; Cirnu and Sanduleac (1965) reported that use of one colony per hectare on 5,582 ha increased seed production 21 to 27 percent, with bees brought in when 5 percent of the plants were in bloom.
Ponomareva (1958) conducted large-scale experiments with bees during 1950-56 on 66 sunflower farms in various Russian zones. When one colony per hectare was placed by the fields, the bees worked "sufficiently well at pollination and honey-gathering within a radius of 500 m of the apiary." Beyond that distance, seed production dropped rapidly. Overall, the fields that were supplied with bees produced 79 percent more seed than fields not supplied with bees. In 22 districts, where one-half colony per hectare was used, production was 890 kg/ha of seed; whereas, in 19 districts, where one colony per hectare was used, seed production was 1,270 kg/ha - an average increase of more than 42 percent. The number of colonies necessary for maximum production was not determined.
Lecomte (1962) counted 108 bees on 100 sunflower heads in the morning and 100 to 115 per 100 heads of cv. 'B-65-40' in the afternoon, and calculated the bee population in the field at 100,000 per hectare. This would indicate about one bee per head and 100,000 heads per hectare. If these heads contained 1,000 to 4,000 florets each and required 10 days to open, there would be an average of 10 to 40 million new florets per day.
Avetisyan (1965) calculated that only 2 million florets per hectare were available daily, and that each floret should be visited eight times; therefore, 16,000,000 bee visits per hectare per day are required. He further calculated that a foraging bee will visit 1,080 florets per day; therefore, 15,000 foragers could pollinate 1 ha. He reasoned that a colony with 6 kg of honey bees would supply enough foragers to adequately pollinate 2 ha of sunflower, providing the bees have nothing else to work on. This population is far below the 100,000 bees, or one bee per sunflower head, observed by Lecomte, and would seem to be an inadequate forager population for highest seed production.
Avetisyan (1965) based his recommendation on the assumption that there was nothing else for the bees to visit except sunflower, that each forager visits sunflower, and that the number of florets is the same each day. Actually, there are almost always competing plants, the number of florets is greater than the average during the peak of flowering, and many colonies do not contain 6 kg of bees. Allowances should be made for such differences when recommendations are issued. This need for allowances is supported by Benedek et al. (1972) who studied the relation of colony numbers, density of bees on the sunflowers, and seed production. They concluded that seed production is dependent upon density of honey bees on the flowers, but that many factors override the effect of colony concentration around the sunflower field and seed production.
To prevent the sharp decline in production with distance from the apiary, the Russians recommended "converging or saturation pollination" or the distribution of the apiaries in such a way that equal distribution of bees throughout the field is obtained. This is basically the method advocated by Todd and Crawford (1962) of distributing the bees every tenth of a mile in each direction in the field, a method utilized in most alfalfa fields today in Western United States.
Khalifman (1959) stated that heavy honey bee visits to sunflowers not only increased seed set but also limited the damage by the sunflower moth (Homoeosoma nebulella Denis & Schiffermuller), a delayed effect called hysteresis. Martin (1968) considered H. electellum (Hurst) the most serious pest of sunflower in South Carolina. Teetes and Randolph (1970) stated that the period of greatest sunflower moth oviposition was the third to sixth day after the sunflower head began to bloom. This is when the pollinating agents should also be at their peak; however, the use of insecticides highly toxic to honey bees is recommended for this same period. Both control of this harmful moth and the use of insect pollinators are necessary for production of sunflower seed. Unless the programs are so arranged that both are successful, seed production is doomed to failure.
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44 See footnote 43, p. 345Pollination Recommendations and Practices:
All research on sunflower pollination indicates that honey bees are the primary pollinating agents, and that colonies should be provided to the field (Barbier and Abid 1966), and that they should be protected from harmful pesticides while they are in the field. The bees should be ready for the pollination task at the onset of flowering. The total flowering period is usually about 20 days, but 83 percent of the heads begin to open within 3 days after the first head opens. Evidence also indicates that the highest bee population and the highest production occur within a few hundred feet of the apiary. If adequate pollination throughout the field is provided, there should be no significant gradient of seed set in relation to apiary location.
The term "saturation pollination," meaning the patterned distribution of groups of colonies, sometimes used on other crops to provide adequate coverage throughout the entire field, is equally applicable and needed in sunflower production. Cirnu (1960) recommended two colonies per hectare, the bees to be moved in at 3 to 5 percent of bloom. Later, Cirnu and Sanduleac (1965) recommended one colony per hectare. Furgala (1954b) recommended one colony per acre, the colonies placed in rows 300 to 400 yards apart. Smith et al. (1971f recommended one-half colony per acre. The evidence is plain that, if the grower wants maximum seed production, he should not skimp on the use of bees.
The number of colonies per acre alone is not too meaningful. Distribution of colonies to give thorough coverage of all blooms is highly important, and strength and other conditions of the colony are equally important. The criterion the grower should use is the bee visits per floret or bees per head throughout his field. The presence of one bee per head throughout the day should provide adequate visitation, but additional research is needed to determine the exact bee population needed for maximum production of sunflower seed.
LITERATURE CITED:
ANONYMOUS.
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1957. POLLINATION OF SOME OILSEED CROPS BY HONEY BEES. Tex. Agr. Expt. Sta. Prog. Rpt. 1960, 5 pp.ARNASON, A. P.
1966. RECENT STUDIES IN CANADA OF CROP POLLINATION BY INSECTS. In 2d Internatl. Symposium on Pollination, London. Bee World 1964: (supp.) 107-124.AVETISYAN, G. A.
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1957. [NECTAR PRODUCTION ON SUNFLOWERS IN THE STEEPE REGION.] Apicultura 30: 9-10. [ In Romanian. ] AA-305 /60.BARBIER, E. [C.], and ABID, M.
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1972. THE NUMBER OF COL0NIES AND THE DENSITY OF HONEYBEES IN SUNFLOWER FIELDS IN RELATION TO THE POLLINATION OF THE CROP. Zeitschr. f. Angew. Ent. 71: 385-389.BITKOLOV, R. S.
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FURGALA, B .
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______ 1960. [ECONOMIC ESTIMATION OF SUNFLOWER POLLINATION WITH THE HELP OF BEES AND BY HAND.] Pchelovodstovo 37(1): 22-25. [In Russian.] AA-445/63
LECLERCQ, P.
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______and HEISER, C. B., JR.
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