LIMA BEANS
Phaseolus lunatus L., family LeguminosaeIn 1970, 70,630 acres of lima beans were grown for processing. The crop was valued at $14.5 million. USDA Agricultural Statistics no longer reports the fresh market acreage.
Plant:
The majority of the acreage is devoted to the bush type of lima beans, an annual with a somewhat woody stem and determinate type of growth, about 2 feet high. The vining, climbing, or pole type may grow to 10 feet and has indeterminate flowering habits, so that fruit is continually produced as long as climatic conditions favor plant growth. With determinate types, most of the inflorescences develop about the same time, which results in a more or less uniform set of fruit. In fact, satisfactory yields are dependent upon obtaining a "capacity set" of pods (fig. 124) during the first 2 weeks of the blossoming period (Hawthorn and Pollard 1954*). Lima beans require a long growing season, but without excessively high temperatures, such as is found along the coast of southern California and in Delaware.
[gfx] FIGURE 124. - Lima bean pods.
Inflorescence:
The white or cream-colored, legume-type flower of the lima bean is borne at the end of a pedicel on a 2- to 4-inch-long raceme. Usually, only a small percentage of the flowers on a raceme set. Various reasons for this failure have been given, including high temperature and low humidity (Cordner 1933), improper soil moisture (Lambeth 1950), and inadequate pollination (Amos 1943). In the flower itself, the keel is elongated into a spirally twisting beak. The style, which follows the spirals of the keel, is also twisted. It is bearded below the stigma (fig. 125). Knuth (1908*, pp. 339 - 340) stated that the stigma, and a portion of the spirally twisted style with pollen adhering to the brush of hairs, projects from the tip of the keel petal when this is depressed and returns again when the pressure is removed. The anthers surround the style and shed their pollen upon it, but the stigma is never dusted before it is exserted. If the stigma is pollinated by the insect visitor before it is touched by its own pollen, cross-pollination can result.
Anthesis occurs between 7 and 8 a.m. The flower never closes, but the corolla is shed after a few days. Nectar is secreted at the base of the corolla and is the source of a fine quality honey. Bees also visit the plant for its pollen. Nectar secretion seems to be greatest when plants first come into bloom, and it remains intense for about a week - then tapers off.
[gfx] FIGURE 125. - Longitudinal section of 'Murphy' lima bean, x 7. Inset shows tip of keel and stigma protruding, enlarged.
Pollination Requirements:
Magruder and Wester (1942) caged plants and concluded, without taking data, that set of pods on most families under the cloth was as good as, if not better than, on uncovered plants. However, Amos (1943) caged plots to exclude bees, and compared production with plots that were shaded, but otherwise left open to bee visitation. He reported about a 30 percent increase in yield due to the presence of bees. He stated that 30 colonies were within 1 mile of the test plots, but the acreage of beans in bloom was not given. Because the observations were made in an area of commercial lima bean production, there could have been hundreds of acres of beans and the honey bee colony per acre ratio could have been quite low. The increase was in numbers of pods, beans per pod, and total weight of beans. He gave no indication as to the pollinator density in the field.
Wester and Jorgensen (1951) found hybrid vigor in all lima bean crosses tested, with production exceeding the best parent in all cases. They stated that a high percentage of crossing was needed. Others have noted that this occurs naturally in some areas now (Magruder and Wester 1940, Barrons 1939, Welch and Grimball 1951, Magruder 1948).
Allard (1954) caged plants with and without bees to obtain a measurement of bee activity in terms of hybrid beans produced. He obtained 2.38 percent hybrids from caged plants visited by bees, and 1.06 percent in cages from which bees were excluded. In open plots dusted with DDT, he obtained 0.21 percent hybrids; but in other plots not dusted, he obtained 1.48 percent hybrids. These experiences and observations indicate that the lima bean, like other beans, is capable of self- pollination but cross-pollination can and does occur. The amount of crossing and its value seem to depend upon the number and species of insect pollinators present or the degree of insect visitation to the crop.
Boswell (1961) stated that the lima bean does not benefit from the intervention of insects; however, other works are not in complete agreement.
Pollinators:
Allard (1954) gave thrips credit for the cross-pollination he obtained. In the light of other research on lima beans, as well as on thrips as pollinators, his data are quite open to question. Incidentally, Mackie and Smith (1935) also gave thrips credit for cross-pollinating beans. Jones and Rosa (1928*) noted that honey bees, bumble bees, and other insects visit the flowers and cause cross-pollination.
Vansell and Reinhardt (1948) compared production from caged and open plots and also from areas of high and low general bee activity throughout the flowering period. They noted that 34.4 percent of the flowers set in the area where bee activity was high and continuous, but only 5 to 22 percent set where insecticides were applied. Because of the insecticide applications, most of the colonies were moved away during part of the flowering period, resulting in low pollinator activity. In fact, they recorded one bee per yard of row before the evacuation of the colonies began, but only one bee per 33 yards of row afterwards. Yet even with this low bee activity, they reported a greater yield in both number and weight of beans from open than from the caged plants. Wester and Jorgensen (1950) stated that bumble bees and honey bees were responsible for most of the lima bean crossing in the field. Anderson (1959) reported that lima bean plants caged with bees set more beans during early blooming period, and the beans were larger than in cages where bees were excluded. He reported that bees visited lima beans in abundance.
Pollination Recommendations and Practices:
Despite the rather promising results on the value of ample insect pollination on the increased production of lima beans by Amos (1943) and Vansell and Reinhardt (1948) and the intriguing study by Drayner (1956) on the value of cross-pollination to increased production of subsequent crops, there has been no follow-up. Beekeepers move their bees to lima bean fields to obtain honey crops, and some growers encourage placement of apiaries in the vicinity of their crops, because they feel that the bees "help." The number of pollinators supplied to crops in this manner is probably not sufficient for maximum activity on the blossoms. The use of bees as pollinators of lima beans is not recommended by the States in which these crops are grown, nor are there data to indicate the appropriate pollinator population desired for maximum production. Studies leading to such a recommendation are needed. In the interim, the meager data available would indicate that growers would materially benefit if they arranged for placement of numerous colonies in and adjacent to their lima bean fields at flowering time and took steps to protect these pollinators from harmful pesticides
LITERATURE CITED:
ALLARD, R. W.
1954. NATURAL HYBRIDIZATION IN LIMA BEANS IN CALIFORNIA. Amer. Soc. Hort. Sci. Proc. 64: 410-416.AMOS J. M.
1943. A MEASUREMENT OF THE VALUE OF BEES IN THE POLLINATION OF LIMA BEANS. Amer. Bee Jour. 83: 240 - 241.ANDERSON, E. J.
1959. TWO PART POLLINATION PROGRAM CARRIED OUT ON UNIVERSITY FARMS. Penn. Beekeeper 34(3): 4 - 8.BARRONS, K. C.
1939. NATURAL CROSSING IN BEANS AT DIFFERENT DEGREES OF ISOLATION. Amer. Soc. Hort. Sci. Proc. 36: 637-640.BOSWELL, V. R.
1961. FLOWERING HABITS AND PRODUCTION OF SEEDS. U.S. Dept. Agr. Yearbook 1961: 57 - 64.CORDNER, H. B.
1933. EXTERNAL AND INTERNAL FACTORS AFFECTING BLOSSOM DROP AND SET OF PODS IN LIMA BEANS. Amer. Soc. Hort. Sci. Proc. 39: 571 - 576.DRAYNER, J. M.
1956. REGULATION OF OUTBREEDING IN FIELD BEANS. Nature 177: 489-490.LAMBETH, V. N.
1950. SOME FACTORS INFLUENCING POD SET AND YIELD OF THE LIMA BEAN. Mo. Agr. Expt. Sta. Res. Bul. 466, 60 pp.MACKIE, W. W., and SMITH, F. L.
1935. EVIDENCE OF FIELD HYBRIDIZATION IN BEANS. Amer. Soc. Agron. Jour. 27: 903-909.MAGRUDER, R.
1948. NATURAL CROSSING OF LIMA BEANS IN SOUTHERN CALIFORNIA IN 1946. Amer. Soc. Hort. Sci. Proc. 51: 471-474.______and WESTER, R. E.
1940. NATURAL CROSSING IN LIMA BEANS IN MARYLAND. Amer. Soc. Hort. Sci. Proc. 37: 731-736.______and WESTER, R. E.
1942. PREVENTION OF FIELD HYBRIDIZATION IN THE LIMA BEAN. Amer. Soc. Hort. Sci. Proc. 60: 413-414.VANSELL, G. H., and REINHARDT, J. F.
1948. DO HONEY BEES HELP POLLINATE BABY LIMA BEANS? Gleanings Bee Cult. 76: 678-679.WELCH, J, E., and GRIMBALL, E. L.
1951. NATURAL CROSSING IN LIMA BEANS IN S. CAROLINA. Amer. Soc. Hort. Sci. Proc. 58: 254 - 256.WESTER, R. E., and JORGENSEN, H.
1950. EMASCULATION UNNECESSARY IN HYBRIDIZING LIMA BEANS. Amer. Soc. Hort. Sci. Proc. 55: 384 - 390.____ and JORGENSEN, H.
1951. HYBRID VIGOR IN lIMA BEANS. Amer. Soc. Hort. Sci. Proc. 57: 305-309.
