Lima beans are native to Central America. Their culture is at least 7000 years old. They were grown by Native American tribes before European Settlers reached the Americas in both the southwestern and east coast regions (Mackie 1943). They were commonly intercropped by native Americans with corn. Today, 40,000 ac of lima beans for processing are grown in Delaware (4249 h +ac), Wisconsin/Illinois/Minnesota and on the NW Pacific Coast (2,226 h in CA, plus in OR & WA). There has been a steady decline in production the last 30 years (by almost 1/2 the hectares in DE alone). The crop was valued at $107 million in 1996. USDA Agricultural Statistics no longer report fresh market acreage - it is not an uncommon garden planting and pole lima's are regionally popular in the south.
The majority of the acreage is devoted to the bush type of lima beans, a perennial cultivated as an annual with a somewhat woody stem and determinate type of growth, about 0.5m high. There is both a large seeded (Fordhook) and a smaller size - they are sometimes called bush baby or butter beans. A third, the vining, climbing, or pole type may grow to 3m and has indeterminate flowering habits, so that fruit is continually produced as long as climatic conditions favor plant growth. For commercial purposes, these categories are recognized: 1. fresh frozen limas (Fordhook), 2. baby frozen limas and 3. dry (grain) limas (Wootten, 1995).
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 (60-110 days), but without excessively high temperatures, such as is found in the coastal environment of the Pacific Coast, particularly southern California, and in Delaware. Harvesting is usually destruct-type when plants have 10% dry pods. Pods are stripped from vines and opened to yield seeds. The beans are processed by freezing or canning relatively rapidly. Most of the commercial plantings are done under processor contract.
The white or cream-colored, legume-type flower of the lima bean is borne at the end of a pedicel on a 5 to 10cm (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 (Lamberth 1950), and inadequate pollination (Amos 1943). Recently, Wootten (1995) found that yield differences between Delaware (east coast) and California (west coast) growing regions were due in part to reflowering at original flower cluster position yielding mature seeds at a higher rate on the west coast and therefore nearly double the yield (4000 kg/h vs 2000 kg/h in DE). 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 exerted. If the stigma is pollinated by the insect visitor before it is touched by its own pollen, cross-pollination can result.
Anthesis occurs between 07:00 and 08:00 h. 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. Nectar secretion seems to be greatest when plants first come into bloom, and it remains intense for about a week - then tapers off. Bees also visit the plant for its pollen.
Magruder and Wester (1940) stated insects were "crucial" to lima bean production but then later (1942), after studies of caged plants, they concluded, without data presentation, that pods set in cages was as good as on uncovered plants. Lamberth (1950) supporting this conclusion. However, when Amos (1943) caged plots to exclude bees, and compared production with plots that were shaded, but otherwise left open to bee visitation, he found about a 30 percent increase in yield due to the presence of bees. The increase was in numbers of pods, beans per pod, and total weight of beans. Amos gave no indication as to the pollinator density in the field.
He stated that 30 colonies were within 1 mile of the test plots, but the acreage of beans in bloom was not given and 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.
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 bee colonies were moved away during part of the flowering period, resulting in low pollinator activity. They recorded one bee per yard of row before colony removal began, but only one bee per 33 yards of row afterwards - even with this low bee activity, there was a greater yield in both number and weight of beans from open than from the caged plants. Caron (1985) found fruit set higher in cages with small nuc colonies of honey bees but differences (no bees, cages with honey bees and open plots) were not statistically different.
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 (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 related to hybrid bean production. 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 in lima bean, like other beans, both self- and 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. Allard (1954) credited thrips for the cross-pollination he obtained in his studies. 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 and cross-pollinate flowers.
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. Hight (1979) found measurable populations of bees (leafcutter, bumble and carpenter bees), syrphid flies, Polistes wasps, skippers and minute pirate bugs visiting lima bean flowers but was not able to evaluate their usefulness as pollinators.
Pollination Recommendations and Practices
Studies by Amos (1943), Vansell and Reinhardt (1948) and Caron (1985) failed to demonstrate an economically feasible increase in production of lima beans when honey bee are utilized for cross pollination. Beekeepers move their bees to lima bean fields to obtain honey crops, and some growers encourage placement of apiaries in the vicinity of their crop, because they feel that the bees "help" (Abrams 1948). 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. The 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 by use of IPM practices (Dively and Caron, 1974).
Abrams, G. 1948. Migratory Bee Culture in MD. MD Agric. Exp. Sta. Bull. A48. 21 pp.
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.
Caron, D. M. 1985. Lima Beans. Glean Bee Cult. 113 (8): 438-439.
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.
Dively, G. and D. M. Caron. 1974. Sweet Corn and Lima Bean Pest Management. Amer. Bee Jour. 114 (6): 213-221.
Drayner, J. M. 1956. Regulation of Outbreeding in Field Beans. Nature 177: 489-490.
Hight, S. 1979. Pollination of Lima Beans. MS Thesis, Univ. of Maryland.
Lambeth, V. N. 1950. Some Factors Influencing Pod Set and Yield of the Lima Bean. Mo. Agr. Expt. Sta. Res. Bull. 466, 60 pp.
Mackie, W. W. 1943. Origin, dispersal, and variability of the lima bean, Phaseolus lunatus. Hilgardia 15:1-29.
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.
Wootten, Tracy. 1995. The effects of heat stress on retention and abscission
of lima bean reproductive structures. MS Thesis, Univ. of Delaware. 197
Revision of INSECT POLLINATION OF CULTIVATED CROPS (McGregor, 1976) by Dewey M. Caron, Univ. of Delaware, July 1999.