WHITE CLOVER55
Trifolium repens L., family LeguminosaeWhite clover consists of three general types - large, primarily 'Lading'; intermediate; and small.
About 16,000 acres were devoted to production of 'Ladino' clover seed in California in 1969. Production of seed of the intermediate and small types came from about 10,000 acres, 4,000 acres of which were in Louisiana, and the remainder in Idaho and Oregon. 'Ladino' seed production was 305 lb/acre; intermediate and small types, 105 lb/acre in Louisiana; and 300 lb/acre in the Idaho-Oregon area (Henderson et al. 1969). California and Oregon are the leading States in production of 'Ladino' clover seed; Idaho leads in production of the other types.
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55 See "Clovers, General."Plant:
White clover is a low-growing, shallow-rooted legume that spreads by creeping stems that root at the nodes (fig. 193). By the end of the second year, the runners of a single plant have formed a dense mat 2 to 3 ft2 with a height of 3 to 24 inches depending upon types and cultivars (Eby 1941). White clover is a short-lived perennial in the Northern States, but in the South it is often used as a winter annual (Wheeler 1960). The crop may be seeded with grasses, but sometimes a pure stand is maintained. It is usually grazed by livestock until the grower is ready for a seed crop to be produced.
[gfx] FIGURE 193. - Individual 'Ladino' clover plant in bloom.
Inflorescence:
The globose, white flower head consists of 50 to 250 (average of 100) florets. Each floret may produce seven but averages about 2.5 seeds (Dunavan 1962, 1953, Dessureaux 1950, Green 1957, Vansell 1951). When a high number of ovules is present, high seed setting results if pollination is adequate (Dessureaux 1951). About 10 florets open daily on a head.
Within the floret, nectar is secreted on the inner side of the base of the staminal tube. The calyx is only 3 mm long so the nectar is easily reached by most nectar-collecting bees. The wing petals are fused with the keel on either side so that both move simultaneously when the keel petal is depressed by a bee visit. This pressure is sufficient to expose the staminal tube, and it touches the underside of the bee. After the bee departs, the staminal tube returns to its original position. When the bee goes to the next flower, the pollen is transferred to its stigma and crossing results. The stigma extends beyond the anthers so selfing is not possible (Knuth 1908*, pp. 284-298).
The intermediate and small types of white clover constitute probably the most important honey producing crop in the United States, and provide also a good source of pollen for the bees. Vansell (1951) and others have indicated that 'Ladino' clover is a poor nectar source and that most of the bee visitors to 'Ladino' flowers were collecting pollen. Oertel (1961) reported that on 'Louisiana' white clover some bees were collecting nectar, some were collecting pollen, and others collecting both. Johnson and Wear (1967) stated that boron caused an increase in the number of seeds of white clover per head. Possible reasons suggested for this increase included increased bee activity and increased number of flowers. Smith and Johnson (1969) observed no increased bee visitation to treated plants in bloom but concluded that boron is necessary for nectar production, which indirectly influences pollination and subsequent seed production.
Pollination Requirements:
Since Darwin's (1889*) original experiment, various workers have shown that white clover is largely to completely self-incompatible. Hollowell (1936) pointed out that this means that pollen must be transported from plant to plant rather than between florets on a plant; thus, the yield of seed depends on the number of flowers and the cross- pollination between plants. Dunavan (1952, 1953) obtained less than three seeds per head in cages where bees were excluded, but 90 seeds with bees present. Williams (1931) obtained 5.8 seeds per head from selfed plants. Palmer-Jones et al. (1962) got no seed set in cages that excluded bees. Weaver (1957a) harvested 12 lb/acre in cages with bees excluded and 82 lb/acre with bees present. Vansell (1951) likewise obtained no seeds from bagged 'Ladino' clover heads, but open heads visited by bees produced an average of 247.6 seeds each. Most of the pods contained 2 or 3 seeds. Martin (1930), Erith (1924), and Williams (1931) noted that self- pollination rarely takes place. Atwood (1941a, 1942) found that self- compatibility varied with plants. Atwood (1941b) associated this variation with cytological interference zones on the stigma and in the style.
Vansell (1951) stated that no 'Ladino' florets opened before 9:30 a.m. and few before 11 a.m. The length of time that florets are capable of being pollinated after they open has not been determined, although Wheeler and Hill (1957*) stated that the floret should be tripped the day it opens.
Florets that are not visited by bees will stay open and fresh looking for a week or longer, but when they are pollinated they wilt within a few hours (Weaver 1957a, b). The grower can determine the degree of white clover pollination by examining the flower head. When pollination is progressing satisfactorily, the head will have wilted florets at the base, buds toward the apex, and no more than a dozen fresh open florets in between.
Pollinators:
The honey bee is the most important pollinator of white clover. The plant is highly attractive to bees ('Ladino' much less so than the intermediate or small types), and bees are likely to be found visiting the flowers to some extent wherever the plants are grown (Atwood 1943).
Bohart (1960*) stated that wild bees are apparently a negligible factor in white clover pollination under commercial conditions; nevertheless, Osmia, Halictus, Tetralonia [Synhalonia], and Bombus are especially fond of white clover blossoms. He stated: "It is probable that there is no shortage of wild pollinators in small seed fields adjacent to good territory for wild bees." Pedersen et al. (1961) stated that bumble bees and many other wild bees were useful.
Honey bees can be moved to white clover fields when desired in whatever numbers desired for pollination (fig. 194). This permits greater dependability than is permitted with wild bees.
[gfx] FIGURE 194. - One of several rows of honey bee colonies distributed uniformly across a 'Ladino' clover seed field.
Pollination Recommendations and Practices:
Harrison et al. (1945) recommended that white clover seed fields should not be more than 2 miles from a beeyard and preferably less than 1 mile. Lancaster (1949) recommended one colony per acre of clover within 1.5 miles. Green (1956,1957) indicated that one colony per 15 to 20 acres was sufficient. Forster (1966) stated that clover within about a mile of a concentration of one colony per 8 acres received ample visits. Weaver (1957a) concluded that under ideal conditions one strong colony should be able to visit all the blossoms open on any day on slightly more than 3 acres of the best stand of clover. Hollowell (personal commun., 1971) stated that these recommendations were far too low. Hollowell (1936) recommended colonies of honey bees in the immediate vicinity of clover- seed producing fields, but later (1942) recommended that colonies be adjacent to the fields.
Oertel (1943) first recommended one or two colonies per acre, then later (1954) recommended not less than one strong colony per acre, but still later (1961) he considered one colony per 3 acres if there was no plant competition for the bees. Paddock (1946) concluded that for every 10 acres, five to ten colonies should be provided. Owen (1953), Lyle (1944), and Eckert (1959*), recommended one colony per acre. They defined a strong colony as one having not less than seven combs of brood and enough bees to cover at least 15 frames in a two-story hive. Wheeler and Hill (1957*), Osterli and Miller (1951), and Miller et al. (1952) recommended one to one and a half colonies per acre. Pedersen et al. (1961) recommended one or two strong colonies per acre. Scullen (1956*) stated that one colony per acre will supply about one bee per square yard but that two bees per square yard were needed, and, if there were more than 127 blooms per square yard, even more bees were needed. Smith (1953) recommended two to three colonies per acre. Smith et al. (1971) recommended one colony per acre. Bohart (1960*) concluded, "The question of the number of colonies per acre (or bees per square yard) for maximum white clover seed production has not been resolved, in spite of the fact that nectar and pollen collectors are apparently about equal in pollinating efficiency, and competition of other plants is not as severe as with many crops."
The best criteria for adequate pollination is either the appearance of the crop or the activity of the bees on it. Weaver's (1957b) statement that flower heads with a hand of withered florets around the base, a band of buds at the top, with a narrow band of open florets in between, affords a satisfactory guide, as does the need expressed by Scullen (1956*) for two or more trees per square yard of flowers. The number of colonies required to provide this population could conceivably vary with every field. The flower evaluation method can be made at any time of day. Bee counts must be made when weather conditions permit bees to fly.
LITERATURE CITED:
ATWOOD, S. S.
1941a. CONTROLLED SELF- AND CROSS-POLLINATION OF TRIFOLIUM REPENS. Amer. Soc. Agron. Jour. 33: 538-545.______ 1941b. CYTOLOGICAL BASIS FOR INCOMPATIBILITY IN TRIFOLIUM REPENS. Amer. Jour. Bot. 28: 551-557.
______ 1942. GENETICS OF PSEUDO-SELF-COMPATIBILITY AND ITS RELATION TO CROSS-INCOMPATIBILITY IN TRIFOLIUM REPENS. Jour. Agr. Res. 64: 699-709.
______ 1943. ``NATURAL CROSSING', OF WHITE CLOVER BY BEES. Amer. soc. Agron. Jour. 35: 862-870.
DESSUREAUX, L.
1950. VARIATION IN THE SEED SETTING ABILITY OF LADINO WHITE CLOVER. Sci. Agr. 30: 507-517.______ 1951. OVULE FORMATION AS A FACTOR INFLUENCING SEED-SETTING OF LADINO WHITE CLOVER. Sci. Agr. 31: 373-382.
DUNAVAN D.
1952. INSECT POLLINATION OF LADINO CLOVER IN SOUTH CAROLINA. Jour. Econ. Ent. 45: 124-125.______ 1953. INSECT POLLINATION OF LADINO CLOVER IN SOUTH CAROLINA. Amer. Bee Jour. 93: 468-469, 487.
EBY, C.
1941. LADINO CLOVER. N.J. Agr. Expt. stat cir. 408, 7 pp.ERITH A. G.
1924. WHITE CLOVER (TRIFOLIUM REPENS L.), A MONOGRAPH. 150 pp. Duckworth Co., London.FORSTER, I. W.
1966. POLLINATION OF WHITE CLOVER. New Zeal. Jour. Agr. 113(2): 50-51, 53.GREEN, H. B. 956.
1956. SOME FACTORS AFFECTING POLLINATION OF WHITE DUTCH CLOVER. Jour. Econ. Ent. 49: 685-688.______ 1957. WHITE CLOVER POLLINATION WITH LOW HONEY BEE POPULATION. Jour. Econ. Ent. 50: 318-320.
HARRISON, C. M., KELTY, R. H., and BLUMER c.
1945. HONEYBEES AND LEGUME SEED PRODUCTION. Mich. Agr. Expt. Sta. Quart. Bul. 28(2): 1 - 5.HENDERSON, W. W., SWEDBERG, J. H., and PERKINS, N. V.
1969. CALIFORNIA SEEDS - LADINO CLOVER SEED FORECAST. Calif. Crop and Livestock Rptg. Serv. U.S. Dept. Agr., Statis. Rptg. Serv., and Calif. Dept. Agr., Bur. Agr. Statis., n.p.HOLLOWELL, E. A.
1936. WHITE CLOVER. U.S. Dept. Agr. Leaflet 119, 8 pp.______ 1942. LADINO WHITE CLOVER FOR THE NORTHEASTERN STATES. U.S. Dept. Agr. Farmers' Bul. 1910, 10 pp.
JOHNSON, W. C., and WEAR, J. I.
1967. EFFECT OF BORON ON WHITE CLOVER (TRIFOLIUM REPENS L.) SEED PRODUCTION. Agron Jour. 59: 205-206.LANCASTER, R. R.
1949. CLOVERS FOR TEXAS PASTURES. Tex. Agr. Ext. Serv. B-168, 24 pp.LYLE, C.
1944. BEES PROMOTE CLOVER SEED PRODUCTION. Miss. Farm Res. 7(12): 1, 4.MARTIN, J. N.
1930. THE SEED PRODUCTION OF CLOVER AND ALFALFA AS RELATED TO BEES. In Pammel, L H., and King, C. M., Honey Plants of Iowa, Iowa Geol. survey Bul. 7, pp. 1075-1080.MILLER, M. D., JONES, L. G., OSTERLI, V. P., and others.
1952. SEED PRODUCTION OF LADINO CLOVER. Calif. Agr. Ext. Serv. Cir. 182, 30 pp.OERTEL, E.
1943. WHITE CLOVER SEED AND HONEYBEES. PROGRESS THROUGH AGRICULTURAL RESEARCH. La. Agr. Expt. Sta. Ann. Rpt., pp. 135-136.______ 1954. THERE'S NOTHING LIKE HONEYBEES FOR [WHITE] CLOVER. South. Seedsman 17: 22, 72-73.
______ 1961. HONEY BEES IN PRODUCTION OF WHITE CLOVER SEED IN THE SOUTHERN STATES. Amer. Bee Jour. 101: 96-99.
OSTERLI, V. P., and MILLER, M. D.
1951. LADINO CLOVER SEED PRODUCTION IN CALIFORNIA. Crops and Soils 4(1): 18-20.OWEN, C. R.
1953. LOUISIANA S-1 WHITE CLOVER. La. Agr. Expt. Sta. Bul. 479, 15 pp.PADDOCK, F. B.
1946. LET'S PUT THE BEES IN YOUR BUSINESS. Successful Farming 44(5): 28-29, 46-48.PALMER-JONES, T., FORSTER, I. W., and JEFFERY, G. L.
1962. OBSERVATIONS ON THE ROLE OF THE HONEY BEE AND BUMBLE BEE AS POLLINATORS OF WHITE CLOVER (TRIFOLIUM REPENS LINN.) IN THE TIMARU DISTRICT AND MACKENZIE COUNTRY. New Zeal. Jour. Agr. Res. 5: 318-325.PEDERSEN, M. W., JONES, L. G., and ROGERS, T. H.
1961. PRODUCING SEEDS OF THE LEGUMES. U.S. Dept. Agr. Yearbook 1961: 171-181.SMITH, H., PANEKIW, P., KREUTZER. G., and others.
1971. HONEY BEE POLLINATION IN MANITOBA. Manitoba Dept. Agr. Pub. 525, 16 pp.SMITH M. V.
1953. LEGUME POLLINATION IN ONTARIO. Ontario Dept. Agr. Cir. 139, 7 pp., rev.SMITH R. H., and JOHNSON, W. C.
1969. EFFECT OF BORON ON WHITE CLOVER NECTAR PRODUCTION. Crop Sci. 9: 75.VANSELL, G. H.
1951. HONEY BEE ACTIVITY ON LADINO CLOVER FLORETS. Jour. Econ. Ent. 44: 103.WEAVER, N.
1957a. POLLINATION OF WHITE CLOVER. Texas Agr. Expt. Sta. Prog. Rpt. 1926, 4 pp.______ 1957b. THE POLLINATION OF WHITE CLOVER. Amer. Bee Jour. 97: 317-318.
WHEELER, W. A.
1950. FORAGE AND PASTURE CROPS. 752 pp. D. Van Nostrand Co., Inc., New York.WILLIAMS R. D.
1931. SELF- AND CROSS-STERILITY IN WHITE CLOVER. Welsh Plant Breed. Sta., Ser. H(12): 209-216.
