Grain legumes are important dietary constituents worldwide
even though their overall production lags far behind that of the
cereals. Yields per unit area are generally less than one-half
those of the major cereal grains. There are several reasons why
grain legume yields in general and those of lentil (Lens culinaris
Medik.) in particular have lagged behind: relegation of these
crops to poorer soils, minimal research efforts until very recently,
and various abiotic and biological limitations. The biological
constraints relate to the large amounts of energy needed to absorb
large concentrations of protein, and sometimes oil, into seeds
in contrast to the energy required by cereals, which primarily
store carbohydrates. Also, photorespiration consumes about 30
percent of the products of photosynthesis, and the symbiotic relation
between the Rhizobium microsymbiont and its legume host
reduces production potential by about 10 percent, as the plant
diverts carbohydrates to nodulated roots for use during dinitrogen
fixation (Evans 1980, Hymowitz
1987).
Energy requirements are critical for legumes because of their
indeterminate growth and progressive flowering and seed-setting
habits, compared with the synchronous flowering of cereals (Evans 1980). In addition, grain
legumes are often grown in marginal arid areas where they seldom
receive fertilizer, irrigation, or pest control chemicals. Indeed,
they are often not planted or given agronomic care until cereal
crops have been well established (Summerfield
1981b.)
Research and breeding efforts devoted to legume crops are small
compared to those devoted to cereals. For example, the number
of accessions in germplasm collections of major cereals is up
to one order of magnitude larger than those of legumes. There
is great discrepancy, too, in the number of breeders working with
legumes compared to the cereals. For example, there are at least
10 times as many maize breeders as there are soybean breeders
in the United States (Hymowitz
1987). Despite these imbalances in resources, remarkable progress
in applied legume science and legume breeding has been made in
recent years, especially in tropical regions, due primarily to
the work of the system of international agricultural research
centers (the CEIAR). The International Center for Agricultural
Research in the Dry Areas (ICARDA),
in Syria, is the unit within CEIAR with a world mandate for lentil
improvement. It is widely expected that plant breeding efforts
at ICARDA and in national programs elsewhere will lead to substantially
increased lentil yields.
Cereal production worldwide exceeds that of grain legumes by
at least 30 times; cereals occupy about 10 times more land and,
on average, are 3 times as productive (table
1). Lentils contribute about 4.6 and 2.5 percent, respectively,
to the supply of edible pulse crops worldwide and in the United
States (Food
and Agricultural Organization 1991).
A description of the lentil crop, together with methods of
production, available cultivars, and crop improvement efforts,
are reviewed herein.
Lentils have been grown commercially in the Palouse
region of eastern Washington and northern Idaho since 1937
(Youngman 1967). The Palouse
includes the region of loess rolling hills with elevations up
to 900 m (3,000 ft) and spanning 46–48 °N latitude. The
higher elevations of the Palouse are located in an area of northern
Idaho known as the Camas Prairie. Although the number of farms
have decreased in recent years, the areas sown to lentils have
increased. These increases reflect the rising demands from foreign
markets, as well as those of an expanding domestic market. In
1990, lentil exports from the United States increased by 15 percent
and had a value of $31.7 million; the corresponding domestic market
value was then $6.8 million (USA
Dry Pea and Lentil Council 1991).
Although yellow cotyledon lentils are widely grown in the Palouse
for the domestic market and for export, there is increasing interest
in seed types more common elsewhere. The smaller seeded "Persian"
type with red cotyledons, popular in many areas of the Middle
East, has generated considerable interest among American producers.
National pulse production areas are similar in climate, weather,
and cultural practices. Lentil production is also under way on
limited hectarage in areas such as northwestern Montana and eastern
North and South Dakota. Continued expansion into these areas will
depend on the attitudes of producers, the availability of farming
machinery and equipment appropriate for the crop, and, ultimately,
the relative profitability and certainty of return compared with
alternative crops.
Lentils are most often grown in rotation with cereals. Farmers
consider lentils an important factor in their rotations for several
reasons: (1) soil erosion is reduced when a lentil crop replaces
summer fallow; (2) less severe disease infestations occur in any
following cereal crop because lentils are not an alternative host
for certain cereal pathogens; (3) the rotation provides better
control of grassy weeds compared with cropping systems containing
only cereals; and (4) lentils fix dinitrogen when effectively
nodulated, thus reducing the demand for nitrogen fertilizers and
the depletion of inorganic nitrogen from soil.
Optimum lentil production depends on carefully considered and
prudently selected combinations of cropland, seedbed preparation,
pest control, and timeliness and method of harvest. Lentils are
commonly sold in volatile markets, making informed and astute
marketing strategies an important feature in overall profitability
(Smith 1980). Lentil exports
vary in direct relation to crop production. Production is heavily
dependent on environmental conditions, as the lentil crop is acutely
sensitive to the vagaries of weather and climate.
The International Scene
American producers who are familiar with the crop and who are
accustomed to yields more than double those achieved in many other
countries may be surprised to learn that until recently there
were no global, regional, or even national studies of trends in
lentil production or the reasons underlying those trends. The
first appraisals of the international status and the future potential
of the crop were in a report by Watson
(1979) and in a review of the role of cooperatives in marketing
pulse crops in the United States by Smith
(1980). World lentil production increased 53 percent during
the 1980's until 1990, due to increases in total area sown to
the crop and in overall yield per unit area (Food
and Agricultural Organization 1991). India and Turkey are
by far the world's largest producers (table
3). All the major lentil-producing countries, except Canada
and the United States, are also major consumers.
Lentils can tolerate extreme environmental conditions of minimal
rainfall and hot temperatures, although sensitivity to these stresses,
particularly during flowering and fruit set, can have serious
effects on yield. The crop is able to tolerate drought better
than waterlogged soil. Worldwide, a large proportion of the lentil
crop is grown in semiarid regions without the benefit of irrigation.
In most of those regions where lentils are important, agriculture
depends on water conserved in the soil after fall and winter rains.
Lentils tolerate cool temperatures and can be sown in autumn in
some of the warmer regions. They are, however, intolerant of the
extremely cold, dry winters in some regions. There is considerable
work being done in the United States and Turkey, and by ICARDA
in Syria to improve winter hardiness of the crop.
Lentil cultivation in traditional areas, including northern
Africa, the Middle East, Ethiopia, and the Indian subcontinent,
range from fully mechanized to fully traditional. Planting dates
are from November to December and usually follow cereal planting.
Soils are generally plowed in summer and cover-cropped until planting
time, although planting on untilled land is also practiced, especially
by subsistence farmers or on fields that are not machine accessible.
Planting rate varies from 40 to 90 kg/ha, depending on whether
the seed is broadcast or planted in rows. If planted in rows,
the spacing varies widely (from 20 cm to 2 m). Often, lentils
are planted in pairs of rows, with 20 cm separating each row and
80 cm separating adjacent pairs. This spacing allows cultivation
between rows to eliminate weeds. Mechanized planting with cereal
drills is becoming more common and inter–row spacings of
40–50 cm are usually used. In traditional production systems,
herbicides are not used; hand weeding is often practiced, with
the weeds then used as animal feed.
Lentil harvest is most often accomplished by hand pulling and
piling the plants in the field for drying. The piles are then
collected and taken to a central threshing facility. Threshing
is usually done by animals and animal-drawn disks, which continually
pass over the piles of plants until the seeds are separated from
the pods. The threshed material is winnowed to separate the seeds
from the straw and other plant debris. The residues from winnowing
are valued as feed for livestock and often command a price equal
to or greater than that of the seeds (Erskine, personal communication
1992). Most of the seed crop harvest is consumed locally, but
the excess is sometimes exported. These traditional methods of
lentil production and harvest are slowly giving way to mechanized
culture, including seed drills, rollers, herbicide applications,
mowing machines, stationary threshers, and in some cases, combines.
Taxonomic and Historical Perspectives
After a confused and complex taxonomic history, lentils were
eventually placed in the genus Lens Miller. The cultivated
form is Lens culinaris Medik. spp. culinaris. It is within
the order Rosales, suborder Rosineae, family Fabaceae, subfamily
Papilionaceae, and tribe Vicieae. Four wild subspecies are recognized
in the genus Lens: L. orientalis, L. nigricans, L. ervoides,
and L. odemensis. Archeological evidence, together with
morphological and cytogenetic comparisons, suggest that L.
culinaris was derived from L. orientalis (Zohary
1972, Ladizinsky 1993).
Ladizinsky (1979a)
indicated that pod indehiscence of cultivated lentil is governed
by a single recessive gene. It is probable that the domestication
of lentils was, to a large extent, the result of selection of
an indehiscent pod mutant from L. orientalis by early agriculturalists
(Ladizinsky 1979b). Lentils
were probably one of the primary domesticates (as were wheat and
barley) on which Neolithic agriculture was founded in the Near
East about 8,500 years ago. By the Bronze Age, they had been disseminated
throughout the Mediterranean region, Asia, and Europe. Lentils
were introduced into the United States in 1916, near Farmington,
Washington (Youngman 1967).
The commercial production of U.S. lentils today can probably be
traced to that introduction of a single landrace. Although generations
of farmers and processors have certainly selected better adapted
cultivars from that original landrace (for example, by saving
seeds for subsequent crops from particularly productive fields
or by planting seeds that were sorted for size), the principal
goal for modern breeders is to have larger and more stable yields.
Lentil Description
Lentils are slender, semierect annuals, usually between 30
and 45 cm (12–18 inches) tall. Individual plants may vary
from single stems to vigorous, bushy forms in dense or sparse
stands. The pinnate leaves are relatively small compared with
the trifoliolates of soybean and Phaseolus beans and may
contain as many as 14 sessile, ovate, elliptic, obvate, or lanceolate
leaflets, each about 1–4 cm (0.5–1.5 inches) long. Each
leaf is subtended by two small stipules and may or may not terminate
in a tendril.
Reproductive nodes generally bear single flowers, sometimes
two or three and, rarely, four flowered racemes on short peduncles.
The typical butterfly-like (papilionaceous) flowers are small,
from 4 to 8 mm (less than ½ inch) long, and white, pale purple,
or purple black. Flowering in lentils proceeds acropetally, so
lower nodes may bear pods close to maturity while younger nodes
continue to initiate flowers. The flowers are self-pollinated,
with cross-pollination vectored by thrips or other small insects
but not by wind or honeybees. Outcrossings due to small insects
are estimated to be less than 0.8 percent (Wilson
and Law 1972). Pollination occurs before the flower opens.
After opening, the corolla fades within 3 days, and the fruits
or pods are visible 3–4 days later. The oblong pods are flattened,
smooth, 1–2 cm ( ½ – ¾ inch) long, and usually
contain 1 or 2, but rarely 3, seeds. Lentil seeds are often divided
into two types, as originally described by Barulina
(1930) as follows (fig. 1):
Macrosperma—found mainly in the Mediterranean
region and the New World, have large seeds [6–9 mm (less
than ½ inch) in diameter], normally yellow cotyledons, and
little or no pigmentation in the flowers or vegetative structures.
Lentil seeds are lens shaped and weigh about 2–8 g per
100 ( 1/8 – ¼ oz per 100). Testa
colors range from pale tan to brown and black, with purple and
black mottles or speckles common to some cultivars (Duke
1981). The seeds are rich in protein with concentrations averaging
26 percent. However, as is often the case in grain legumes, there
is a shortage of tryptophan and the sulfur-containing amino acids,
methionine, and cystine (Adsule
et al. 1989).
The protein in lentils contains significant concentrations
of lycine, a limiting amino acid in cereals. Cereals are relatively
rich in tryptophan and the sulfur-containing amino acids. Therefore,
when cereals and lentils are consumed together in a balanced diet,
they provide adequate amounts of essential amino acids in the
human diet. Seed composition varies with genotype and seed maturity
and is influenced by soil nutrient availability (Summerfield
1981a, Summerfield and
Muehlbauer 1982). These differences are known to affect the
cooking time of mature seeds. Improvement in protein quantity
or quality is unlikely to be an important breeding objective.
Increased quantities of protein from grain legume crops, including
lentils, is most likely to result from breeding efforts directed
toward increased economic yield and stability of yield between
sites and years, rather than from breeding for increased protein
content within lines (Boulter
1977). Lentil seeds are more susceptible to mechanical damage
than field peas, faba beans, and chickpeas. However, germination
is hypogeal (cotyledons remain below the ground), which helps
prevent environmental damage to seedlings. In the event of shoot
damage, new lateral branches can initiate from nodes below ground.
Lentils are nodulated following infection by Rhizobium leguminosarum,
the same species that nodulates pea and faba bean. Nodules are
elongate and seldom exceed 5 mm ( ¼ inch) in length (Summerfield 1981a). Yield
responses to artificial inoculation may or may not be favorable
depending on soil type, availability of inorganic nitrogen, and
previous crops. Further information concerning the genetics, breeding
methods, and hybridization of lentils can be found in Muehlbauer
et al. (1980), Muehlbauer
and Slinkard (1981), Ladizinsky
et al. (1985), and Muehlbauer
et al. (1985, 1988).
Lentil Culture
Land Requirements
Lentils are grown in sandy loam soils, alluviums, black cotton
soils, or in much heavier soils. They may be grown in moderately
alkaline or saline soils; nutrient deficiencies (for example,
phosphate) are common. However, researchers are still unsure of
the precise nutrient requirements of a lentil crop. A general
consensus suggests that molybdenum, sulfur, and phosphorus are
critical elements for good yields. Interactions with the available
water supply also have a large effect on the need and use of minerals
by the plant (Summerfield
1981a).
Knowledge of dinitrogen fixation in lentil is based largely
on systematic work done since 1978. Although Rhizobium leguminosarum
is often indigenous to the areas where lentils are grown, crops
inoculated with specific strains have sometimes been more productive,
depending on the host cultivars. Various studies of dinitrogen
fixation by lentil have indicated values ranging from 35 to 115
kg/ha (31–103 lb/acre). Values at the lower end of this range
would lead to an average lentil crop that depletes soil nitrogen.
Other work indicates that for well-nodulated crops, the fertilizer
needs of a subsequent cereal can be reduced if the preceding crop
is lentils rather than nonlegumes.
Palouse lentil crops are usually sown in the spring in a 2-year
rotation alternating with winter wheat or in a 3-year rotation
alternating with winter wheat or barley. Lentils are commonly
followed by winter wheat because the moisture they remove from
the soil is usually fully replenished by fall and winter rains.
Lentil crops in the Palouse yield best when grown on well-drained
soils on south- and east-facing slopes. Dry seedbeds should be
avoided, as should those areas which remain waterlogged until
late in the season.
Seed Quality and Seed Treatment
For optimum stands and yields, growers must use good-quality
seed. They should use seed that is certified for minimum standards
of germination (greater than 90 percent), free of weed seed and
foreign matter, and treated with seed protectants. In the Palouse,
foundation seed of varieties can be obtained directly from the
Washington State Crop Improvement Association1
or the University of Idaho Foundation
Seed Program.2 Registered and certified seed may
be obtained from seed companies or the processors of the commodity.
The names and addresses may be obtained from the USA Dry Pea and
Lentil Industry Office (see appendix
for address).
Seed treatments with appropriate fungicides, such as captan
or metalaxyl, will prevent damping-off and ensure good stands.
Treatment of the seed with an insecticide such as lindane is beneficial
for the control of wireworms and seedcorn maggots. Molybdenum
is often applied along with the other seed dressings. If lentils
are to be sown in regions outside the Palouse, Rhyzobium leguminosarum
must be placed with the seed to ensure good root nodulation and
dinitrogen fixation.
Seedbed Preparation
Fields intended for lentils are usually chisel plowed in the
fall to aid water infiltration, control erosion, and maximize
the retention of crop residues. Tillage along the contours of
hills improves moisture infiltration and prevents excessive runoff
and soil erosion (Papendick
and Miller 1977). In the spring, when soils are sufficiently
dry, fields should be cultivated and firmed with a spring-tooth
harrow or a rod weeder. Deep tillage leads to excessive loss of
moisture and should be avoided. A well-prepared seedbed will have
some crop residues on the surface, which improves water infiltration
and reduces the erosive effects of rainfall. Excessive residues
interfere with placing seeds at a uniform depth. Soil temperatures
increase quickly when fields are well prepared, resulting in rapid
germination, good emergence, and improved seedling growth.
Seeding
Lentils are often planted in early spring with double disk
drills, the same equipment used to seed cereals. Experience in
the Palouse is typical of that elsewhere: Yield advantages due
to early planting can be substantial, provided seeds are not "mudded
in" by attempting to plant when the soil is too wet (Entenman and Youngman 1968).
Studies indicate that a seeding depth of 4–5 cm (1.5–2
inches) is optimal for germination and growth, even though deeper
plantings may have better access to soil moisture and improved
protection from frost. Despite some success with deeper plantings,
plant emergence may be poor due to soil compaction from farm machinery
or heavy rains. Lentil seeds can germinate in the light or the
dark and in constant or diurnally fluctuating temperature regimes.
However, rates of germination, emergence, and seedling growth
are markedly affected by temperature. Optimum values for germination
and growth vary with cultivar, age, and size of seeds. Smaller
seeded cultivars germinate more rapidly than larger ones at temperatures
between 15 °C and 25 °C (60–77 °F) (Saint-Clair
1972).
The successive stages of canopy formation (stem elongation,
leaf initiation, leaf expansion, and branching) have different
optimal thermal regimes, which obviously affect the rates at which
these processes occur. This may explain a common observation by
farmers that lentil seedlings, once emerged, often grow slowly,
if at all, for several days or even weeks (for example, successive
stages of vegetative development have warmer temperature optima).
Many studies show that lentil yields are remarkably stable
over a wide range of population densities. The plants are able
to fill available space by initiating lateral branches and, thus,
can compensate for poor emergence and thin stands. Recommended
seeding rates for Palouse farmers are 67–79 kg/ha (60–70
lb/acre) for the most commonly grown cultivar 'Brewer' (Morrison
and Muehlbauer 1986). Elsewhere, seeding rates vary from 15
kg/ha (13 lb/acre) in northern India to 115 kg/ha (103 lb/acre)
for irrigated crops in Egypt (Hawtin
et al. 1980). It is always important to use seeds of good
quality and a seeding rate large enough to ensure good stands
in case the crop should suffer adverse environmental conditions,
resulting in poor emergence and disrupted seedling distribution.
Optimum plant density has been estimated at 90 plants/m2
(8.3 plants/ft2)(Muehlbauer
1973).
It is important to select plant populations appropriate for
dryland farming systems. Smaller seeded cultivars are considered
to be more tolerant of drought than the larger seeded ones because
they often mature more rapidly, thus avoiding extreme water stress.
The development of drought-tolerant cultivars deserves to be given
priority in lentil research. Without a doubt, the success of lentils
as an internationally important crop depends greatly upon the
production of economically attractive and reliable yields when
the water supply is limited.
Lentil Cultivars
The few lentil cultivars released before the 1980's were generally
selections from germplasm collections and not from hybridization
programs (Hawtin et al. 1980).
Today, national and international lentil improvement programs
provide much-improved resources for hybridization and selection.
Each of these programs acknowledges the importance of collecting,
introducing, exchanging, and maintaining germplasm to provide
the widest range of genetic diversity in breeding programs. Thus,
with greater attention worldwide and with ongoing nationally and
regionally supported programs, improved cultivars with larger
yield potential are increasingly available. Here are cultivars
currently used by growers in the Palouse—
'Chilean 78' is a composite of pureline selections from 'Chilean',
which were made to remove off-type lentils and Vicia rogues
from the seed stock. The 'Chilean' stock was the most commonly
grown type in the region until the release of 'Chilean 78'.
'Brewer', developed in the hybridization program and released
in 1984, has largely replaced common 'Chilean' and 'Chilean 78'
(Muehlbauer 1987). 'Brewer'
has yellow cotyledons and larger, more uniform seeds, matures
4–7 days earlier, and gives consistently higher yields than
'Chilean' (23 percent greater in yield trials). It is currently
the main cultivar grown in the Palouse region.
'Redchief', released in 1980, is a large, red cotyledon-type
cultivar with seedcoats that lack mottling (Wilson
and Muehlbauer 1983). Its yields are consistently better than
'Chilean' or 'Chilean 78'. The domestic market for large, red
lentils is expanding in the United States following the introduction
of 'Redchief'.
'Emerald', released in 1986, is a bright, green-seeded cultivar
with distinctive green cotyledons. Its production is directed
at speciality markets (Muehlbauer
1987).
'Palouse' is a large, yellow cotyledon-type cultivar that was
developed through hybridization and selection for seed size, absence
of seedcoat mottle, and early maturity (Muehlbauer
1992). It produces yields comparable to 'Brewer' and is resistant
to mechanical damage during threshing and processing.
'Crimson' is a small-seeded, red cotyledon-type cultivar, released
in 1990 (Muehlbauer 1990).
Its source was a pureline selection from 'Giza–9', a cultivar
developed in Egypt. It is anticipated that small, red cotyledon-type
cultivars will find a place in the export market.
'Spanish Brown' or 'Pardina' is a small, yellow cotyledon-type
cultivar with brown and speckled seedcoats. It was introduced
from Spain and is now being produced extensively in the Palouse.
It has produced exceptionally good yields, although recent observations
indicate susceptibility to Ascochyta blight caused by Ascochyta
fabae f. sp. lentis.
Other cultivars include 'Laird' (has some Ascochyta blight
resistance and large, unmottled seed) (Slinkard
and Bhatty 1979), 'Eston' (small, pale-colored seed), 'Rose'
(red cotyledons), and 'Indianhead' (small seeded with black seedcoats)
from Canada; 'Precoz' (an early variety) from Argentina (Riva
1975); 'Araucana–INIA' (rust tolerant) from Chile (Tay et al. 1981) and 'Tekoa' (a
U.S. release grown in Chile because of its resistance to rust);
'Pant L–234' (Fusarium resistant) (Kamboj
et al. 1990), 'Pant–209' and 'Pant–406' from India;
and 'Giza–9' from Egypt (Hawtin
et al. 1980).
Fertilization
and Pest Control
Fertilizers
Although researchers are not yet certain of the nutrients required
by productive lentil crops, worldwide experience has prompted
advisers to recommend applications of the following fertilizers
as economically worthwhile "insurance" for growers:
(1) molybdenum (applied as a seed dressing and essential for good
nodulation and dinitrogen fixation); (2) sulfur (additions improve
seed concentrations of the nutritionally limiting S–amino
acids); (3) phosphorus (also essential for good symbiotic performance
and overall plant growth); and, occasionally, (4) potassium.
Recommended application rates are—
• Molybdenum—sodium molybdate as a seed dressing
at 35 g/ha (0.5 oz/acre).
• Sulfur—applied to crops grown in rotation with
lentils at 17–22 kg/ha (15–20 lb/acre) on deficient
soils.
• Phosphorus—if soil tests (acetate extract) reveal
phosphorus concentrations at 4 parts per million or less, apply
at 44–66 kg/ha (39–59 lb/acre). Strong responses are
common on severely eroded soils.
• Potassium—on sandy or severely eroded soils, 22
kg/ha (20 lb/acre) of potassium oxide may prove beneficial for
yield and improve the cooking qualities of seeds (Wassimi
et al. 1978).
• Nitrogen—effectively nodulated lentil crops seldom
respond to an application of inorganic nitrogen fertilizer.
The "nitrogen hunger" phase, which is often experienced
by grain legumes when crops are seeded early into cool, wet soil
before significant symbiotic dinitrogen fixation begins, can be
avoided by the application of a small starter dose of 10–25
kg/ha (9–23 lb/acre) inorganic nitrogen fertilizer placed
adjacent to, but not in contact with, the seeds (Saxena
1981). Inoculation with an appropriate strain of Rhizobium
leguminosarum is necessary when lentils are seeded into fields
for the first time or after a lapse of several years. Special
care should be taken when using fungicide seed dressings potentially
toxic to Rhizobium. The amount of nutrients removed by
an average lentil crop depends on the relative contribution of
symbiotic dinitrogen fixation and the uptake of inorganic nitrogen
(table 4). Comparing these data
with those of other lentil crops grown in a range of edaphic conditions
and locations may determine if different cultivars assimilate
into seeds with similar or substantially different amounts of
these elements.
Weed Control
Lentils compete poorly with weeds for light, water, and nutrients.
During early stages of vegetative growth and in cool weather,
lentil growth rates are slow and weeds can quickly overgrow the
crop. If not adequately controlled, weed infestations can reduce
yields by as much as 75 percent. Although the period of crop growth
during which competition is most deleterious varies in different
locations, competition from weeds is usually serious and requires
some form of control in order to produce good seed yields.
Hand weeding or mechanical cultivation is not practical because
both of these methods can damage lentil seedlings, increase the
incidence of stem and root diseases, and stimulate more weed seeds
to germinate, which can then create additional problems. Harrowing
or rotary hoeing after emergence has been evaluated, but even
this light tillage operation did not improve weed control (Boerboom,
unpublished data 1992).
Research has shown that some herbicide formulations are effective
with lentils, but there are only a limited number of products
registered for use in lentils in the United States (table
5). Because of this limited herbicide availability, along
with lack of crop competitiveness, the broad spectrum of weeds
requiring control, and unpredictable rainfall, the control of
grass and especially broadleaf weeds is sometimes erratic.
Wild oats, volunteer cereals, and other annual grasses are
common and serious weeds in lentil crops. Wild oats can be controlled
with preplant-incorporated applications of triallate. After crop
emergence, sethoxydim applications will control annual and perennial
grasses.
For broadleaf weed control, imazethapyr can be applied before
planting followed by shallow incorporation or applied preemergence
after planting. Metribuzin can be applied either preemergence
or postemergence or as a split application. Metribuzin has given
good to excellent control of a wide spectrum of broadleaf weeds
with few exceptions. Preemergence applications of both herbicides
require adequate rainfall to distribute the herbicide into the
zone where weed seeds germinate. With excessive rainfall and on
soils with low organic matter, metribuzin may leach deeper into
the profile and cause crop injury. Injury is most severe on the
tops of eroded hills where soils have low organic matter and lentils
may have been seeded too shallowly.
Red lentils, such as 'Crimson', can be grown successfully in
areas of lower rainfall, but dry conditions reduce the effectiveness
of soil-active herbicides, so weed control may be poor.
It is always important that growers refer to herbicide labels
for application directions, rates, and precautions. Precautions
should also be taken when applying sulfonylurea or phenoxy herbicides
to cereal crops adjacent to lentil fields, as lentils can be severely
injured by drifts from these herbicides. Residuals of sulfonylurea
herbicides in soils planted in lentils can be especially damaging
to the crop.
Insects
Lentils are attacked by insects wherever they are cultivated.
Preharvest pests include soil insects that attack seeds soon after
planting or that attack the stems and roots of seedlings. These
include seedcorn maggots [Delia platura (Meigen)], wireworms
(Limonius spp. and Ctenicera spp.), cutworms (Agrotis
spp.), and larvae of weevils (Sitona spp.). Thrips (Frankliniella
spp.), aphids [Aphis craccivora (Koch) and Acyrthosiphon
pisum (Harris)], leaf weevils [Sitona lineatus (L.)],
lepidopterous larvae (Helicoverpa and Spodoptera
spp.), and grasshoppers feed on leaves, stems, and flowers.
Worldwide, the most important insects that damage pods and
seeds are lygus bugs (Lygus spp.), bruchid beetles (Bruchus
spp. and Callosobruchus spp.), and lepidopteran pod borers
[Helicoverpa armigera (Hüb.), Cydia nigricana (F.),
and Etiella zinckenella (Treitschke)]. Bruchid beetles
are also major postharvest pests, except in the United States.
The contribution by van Emden
(1988) is a useful general reference on worldwide insect pests
of lentils and other grain legumes.
Aphids have many natural enemies, including lady bird beetles,
parasitic wasps, lacewings, and syrphid flies, but chemical control
may be necessary if these insects do not keep aphids at subeconomic
levels. Insecticide treatment for pea aphid control should be
considered (1) when an economic threshold of 30–40 aphids
are collected per 180° sweep of a 38-cm (15-inch) diameter
insect net, (2) when few natural enemies are present, and (3)
when aphid numbers do not decline over a 2-day period (Homan
et al. 1991).
Lygus bug feeding on the immature reproductive structures of
lentils causes seed and pod abortion, as well as a serious seed-quality
problem known as "chalky spot" in crops grown in northern
Idaho and eastern Washington (Summerfield
et al. 1982). Lygus bugs feed with piercing, sucking mouthparts
and inject toxic saliva into the immature seed. This forms a depression
around the feeding area and leaves a chalky blemish (fig.
2). Adult lygus bug activity can be monitored during blooming
and podding by making 25 180° sweeps in at least 5 randomly
selected places in a field. Chemical control is warranted when
7–10 adults are collected per 25 sweeps (O'Keeffe
et al. 1991).
The western yellow-striped armyworm is usually a late-season
pest. When heavy infestation develops, larvae can defoliate plants
and consume pods. Insecticides containing Bacillus thuringiensis,
a naturally occurring bacterium that infects lepidopterous larvae
and other pest insects, can be used to control damaging populations.
Diseases
Lentils appear to suffer less from diseases than many other
grain legumes. Some of the more serious problems are discussed
next.
Root rot/wilt complex. Probably the most important disease
problems of lentils worldwide are root rots and wilts caused by
Pythium, Rhizoctonia, Sclerotium, and Fusarium species
(Kaiser 1987). Research is
under way to select strains resistant to the various components
of the complex. Inheritance of resistance to Fusarium wilt
has recently been reported in germplasm from India (Kamboj
et al. 1990).
Two other important diseases of lentil in many countries are
rust and ascochyta blight, especially in wetter areas or during
years with heavy rainfall.
Rust. Rust, caused by Uromyces viciae-fabae Pers.,
is a serious problem in areas with mild temperatures and humid
conditions. Some sources of resistance have been identified, and
progress toward developing resistant cultivars is being made (Khare 1981). Fortunately, rust
of lentils has not yet appeared in the Palouse region.
Ascochyta blight. Blight caused by Ascochyta fabae
Speg. f. sp. lentis Gossen, a seedborne disease, causes
severe damage in many cool, wet regions (fig.
3). Work in several countries has identified good sources
of resistance and these lines are being incorporated into breeding
programs. Ascochyta blight is becoming a major problem in the
United States, and it continues to be an economic problem in the
lentil-producing areas of Canada. Breeding programs have been
initiated to introduce into other lentil cultivars the resistance
shown by the cultivar 'Laird' (Slinkard, personal communication
1991). Infescted seed may be treated with thiabendazole to reduce
the incidence of seedborne A. fabae f. sp. lentis,
but the compound is not registered for use on lentils in the United
States (Kaiser 1987).
Seedborne fungi. In the Palouse, reduced seed quality
can result from infection by different pathogenic fungi, some
of which are also pathogens of chickpeas and peas (Kaiser
1992). The incidence of fungi associated with commercial lentil
seeds in the Palouse varies greatly from year to year and is influenced
by weather conditions, particularly rainfall. The seedborne pathogens
most frequently isolated from discolored Palouse-grown lentil
seeds are Botrytis cinerea, Phoma medicaginis var.pinodella
(= Ascochyta pinodella), and two Fusarium species—F.
acuminatum and F. avenaceum. The amount of rainfall
during July, when the crop is approaching maturity or about to
be harvested, appears to affect the incidence, prevalence, and
severity of seedborne pathogenic fungi. If excessive rainfall
occurs during harvest or when plants are drying in windrows, lentils
that remain on or near the moist soil surface may show seed discoloration
from colonization and infection of the pods and seeds by pathogenic
and saprophytic fungi.
Viruses. Viruses are major disease problems in the Palouse.
Most viruses that infect peas also infect lentils. These include
alfalfa mosaic, bean (pea) leaf roll virus (BLRV), bean yellow
mosaic, pea enation mosaic virus (PEMV), and pea streak. These
viruses are transmitted by pea aphids, generally from infected
alfalfa and clover plants. Control of common viruses is best achieved
by planting resistant cultivars. Control of the aphid vectors
is not generally recommended, as the economic thresholds for the
insects are not known and insecticides are often ineffective in
halting the spread of stylet-borne viruses.
In the Palouse region, PEMV and BLRV are the most important
virus diseases of lentil, but the crop is also a host of pea seedborne
mosaic virus (PSbMV). PSbMV may cause stunting and malformation
of leaves, stems, flowers, and fruits. There may also be a reduction
in yield and the production of smaller, misshapen seeds. Sources
of resistance to PSbMV have been identified and are now being
used in the development of new lentil cultivars (Kaiser
1987). Sources of tolerance to PEMV have also been identified
(Muehlbauer, personal observations 1991) and are being incorporated
into improved cultivars.
Harvesting and Marketing
Harvesting
Harvesting often poses problems and may represent a major constraint
to lentil production in traditional farming systems. To avoid
loss of seeds due to shattering, many farmers in developing countries
pull the crop by hand before it is completely mature and lay the
plants in the field to dry. Hand harvesting is uneconomical, so
mechanizing lentil production has become an important goal for
national and international research programs. To facilitate mechanical
harvest, germplasm has been evaluated for taller, nonlodging plant
types with nonshattering pods. These evaluations have been only
partially successful in reducing seed losses at harvest. Development
of equipment to harvest lentil crops in marginal areas must take
into account short plant stature, stony soils, and uneven soil
surfaces. Equipment has been designed and tested that holds promise
for future mechanization of lentil crops (Saxena
and Goldsworthy 1988).
Palouse farmers generally harvest lentils by mowing and swathing,
or they may combine the crop. Swathing is often necessary to kill
green weeds and allow them to dry so the lentils can be threshed
efficiently. Plants are usually swathed when the pods turn a cream
to golden color; then older pods will be dry and their seeds firm.
Harvesting prematurely does not allow the seeds to fully mature,
and harvesting too late, when pods are overripe, can cause them
to shatter. Moden et al. (1986)
showed there can be losses of up to 55 percent of the potential
lentil harvest, one-third due to pod shatter. This problem can
be minimized by mowing at night or early in the morning when relative
humidities are high and dew deposits are present. If lentils are
cut prematurely or if they receive rain, the windrows must be
turned to allow uniform drying and prevent fungal attack.
Swathed lentils can normally be combined 10–14 days after
mowing. The same combines used for cereals, with a pickup attachment
(pea bar), are used to pick up the plant material. Successful
combining can be achieved when the seeds are "hard"
(that is, the seeds will not dent when bitten) and the cylinder
speed and concave spacing are adjusted to prevent the seeds from
cracking or breaking during threshing. Airflow rates should be
adjusted to blow out chaff but not seeds. Machine groundspeed
should be maintained close to 2.5 km/hr (1.5 mi/hr).
Marketing
Palouse lentil crops are graded according to standards set
up by the U.S. Department of Agriculture, Grain
Inspection, Packers, and Stockyards Administration, in close
cooperation with producers and processors. These standards are
based on sieve size, contaminants, moisture content, and other
quality characters. Graded seeds allow orderly marketing and are
used by sellers and buyers to determine price.
The increase in world population and the displacement of lentils
by cereals in traditional production areas point out the need
to increase lentil production in nontraditional areas. In general,
worldwide lentil yields have not increased significantly, but
the loss of production in traditional areas has been largely offset
by expanded production in Turkey and Canada. These two countries
have dramatically increased their production and are the world's
largest exporters.
Lentils contribute significantly to farm economics in the Palouse
and the United States as a whole. The lentil crop, during the
last decade, averaged over 54,400 metric tons with an approximate
value of $31.7 million annually. About 80 percent of U.S. lentils
are exported. Principal markets for Palouse-grown lentils are
Spain, Peru, Ethiopia, and Venezuela.
Collaboration, Cooperation, and Communication
Research and sales promotion are important to lentil-producing
operations. International research organizations, such as ICARDA,
and the national programs of many countries try to provide information
necessary for improvements in lentil farming. These international
and national efforts must be coordinated to produce the maximum
benefit (see appendix).
The newsletter, LENS,
published since 1974, furnishes an excellent medium for communication
among lentil researchers. Other publications and workshops have
further stimulated work on the crop. The impressive gains made
during the last decade must now be extended to improve lentil
production and marketing in the demanding years ahead.
As the international lentil literature was reviewed, it became
apparent that a uniform system for units of measurement must be
used in descriptions of research and production. The authors used
the System International d'Unites (SI) with English system equivalents
in parentheses. A global acceptance of the growth-stage descriptors
described by Erskine et al. (1990)
is also encouraged.
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