Field Pea Production -- continued (Part 2) See
Part 1
A-1166 (Revised), MARCH 2003
Field pea is a legume crop and has the inherent ability to obtain much of its nitrogen
requirement from the atmosphere by forming a symbiotic relationship with Rhizobium
bacteria in the soil.
Grain legumes vary widely in the proportion of the crop's total nitrogen requirement
that may be met through nitrogen fixation. The total amount of nitrogen fixed by the crop
also depends on favorable growing conditions. Hot temperatures and dry soils during the
later vegetative and early reproductive stages are especially detrimental for N-fixation.
Field peas are among the most highly efficient nitrogen fixing crops and may obtain as
much as 80 percent of their total nitrogen requirement under good growing conditions.
However, for this relationship to occur, the seed must be properly inoculated with the
appropriate strain of Rhizobium bacteria. Producers must be certain that the inoculum
product they obtain is specific for field pea. Use of an inoculum labeled for soybean,
clover or other legume will not allow the nitrogen fixation process to occur. Inoculants
are available in various forms including dry peat, liquid and granular.
Application of inoculant to the seed is an extremely important procedure. Many failures
with nitrogen fixation have been associated with improper application technique. Thorough
coverage of the seed is critical since seeds not exposed to the bacteria will result in
plants unable to fix nitrogen. Inoculants are living organisms, so proper storage and
handling is important.
Granular inoculant, a relatively new form of inoculant, has alleviated many of the
concerns with inoculant applications. This inoculant is metered through the planter and
delivered directly into the seed furrow.
Producers should refer to the manufacturer's package labels to review proper
inoculum rate and handling procedure.
Growers should check their fields to determine if inoculation was successful. Normally,
nodules will form on the roots two to four weeks after emergence. To check for nodulation,
carefully dig up a number of plants and gently clear the soil from the root mass. Nodules
will be present both on the primary root and on the lateral roots. Effective nodules will
have a pink to red coloration on their interior. If nodulation does not occur and soil
nitrogen levels are low, an application of nitrogen fertilizer over the top may be
required to optimize seed yields. Nitrogen fixation will take place from about four weeks
after emergence through seed formation.
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Under most conditions, the use of inoculants will satisfy the nitrogen requirement of a
field pea crop. A soil test should be conducted to determine the status of the primary
nutrients.
Addition of a nitrogen fertilizer may be required when field pea is planted on land
with less than 30 pounds of available nitrate N in the top two feet of the soil profile.
Under these conditions, the addition of 20-30 pounds of nitrogen with commercial
fertilizer is recommended to meet the needs of the developing field pea plant until
nodulation becomes fully effective.
Producers should avoid planting field pea on fields that have a high level of nitrogen.
Excess nitrogen will promote vegetative development over reproductive seed production.
Higher nitrogen levels will also reduce the potential of nitrogen fixation and increase
the potential for lodging.
A rule of thumb is that 1.25 pounds of residual nitrogen per acre is available for
every bushel of peas (field pea has a standard bushel weight of 60 pounds) produced per
acre. For example, 50 pounds of residual nitrogen per acre may be expected from a field
pea crop of 40 bushels per acre.
Beyond nitrogen nutrition, phosphorus fertilization is likely the primary concern for
field pea growers. Research has indicated the importance of adequate phosphorus fertility
for optimizing seed yield. Proper fertilizer source, rate and placement are necessary to
avoid reductions in plant stand while at the same time meeting the P needs of the field
pea plant. Avoid placing fertilizer directly with the seed. North Dakota research has
indicated stand loss is likely while yields are not increased.
Refer to NDSU Extension Service publication SF725,
Fertilizing Field Pea and
Lentil, for additional information that relates to field pea nutrient requirements.
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Field pea is a poor competitor with weeds, especially during the first month after
planting. Relatively slow early-season growth and lack of complete ground cover by the crop
canopy allow weeds to be competitive. Field pea is most competitive with even, rapid
emergence. A well-established stand of seven to eight plants per square foot is critical
for field pea to be competitive with weeds.
Perennial weeds and annual weeds that emerge early in the season, including common
lambsquarters, kochia, volunteer grain, wild mustard and wild oat, are very competitive
with pea. For example, a Canadian trial indicated that two wild mustard plants per square
foot reduced pea yield as much as 35 percent. Good weed control is also very important in
raising high-quality human edible pea. Weeds such as kochia, Russian thistle, nightshade
and wild buckwheat can cause harvest problems with fields that are intended to be straight
combined. Nightshade berries can stain the pea seed, causing a reduction in quality.
Cultural methods that should be used as part of an integrated weed management system
include crop rotation, field selection, rapid crop establishment at an adequate density
and use of clean seed. Pre-emergence or early post-emergence tillage with a rotary hoe or
harrow can reduce populations of shallow-emerging weeds such as common lambsquarters,
foxtail, kochia and pigweed. Post-emergence tillage with a rotary hoe or light spring-tooth
harrow needs to be timed to control emerging weeds on small (half to two-inch tall) field
pea. Pea stand reduction probably will occur with post-emergence tillage.
There are several soil-applied and post-emergence herbicides labeled for weed control in
field pea. Generally, post-emergence herbicides should be applied to small weeds and pea
(two to four-inch height) to maximize weed control and minimize crop injury. Pre-harvest
desiccants also are labeled to dry weeds for a more efficient harvest.
For a listing of registered herbicides and directions for use, consult NDSU
Extension Service publication W253,
North Dakota Weed Control Guide, and herbicide labels.
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Controlling disease in field pea begins with crop rotation. A preferred crop rotation
would have field pea planted with at least two cropping years between plantings. Long-term
crop rotational research in Canada indicates that a rotation of small grain/canola, or
flax or lentil/small grain/field pea has been successful without any major buildup of
disease.
Mycosphaerella and ascochtya foot rot are the main diseases of economic importance in
field pea. It is often difficult to distinguish between these diseases in the field. They
are fungus diseases that cause purple spots or lesions on the leaves, stems, flowers, pods
and seeds.
Disease is most severe with continuous wet weather. Fungal spores may spread by
splashing rain to uninfected tissue. Severely infected leaves will prematurely die,
resulting in premature ripening of the plant. Lesions on pods can develop, which may
result in the seed becoming infected. Infected seed will be shrunken and discolored.
Ascochtya foot rot will form blackish-purple lesions on the stem at the base of the plant.
Severe infections will result in premature ripening, lodging, shriveled seed
and reduced yields.
Both fungi survive on plant debris, and spores can survive for years on field pea
stubble. Spores of both fungi can also be carried on the seed; therefore, planting
disease-free seed is very important. Producers who buy or use their own seed should know
the level of seed-borne inoculum present on the seed.
Aphanomyces root rot is another disease that can affect field pea. Aphanomyces root rot
is caused by a fungal-like organism. It overwinters in the soil as thick-walled spores
(oospores) that can survive for many years. In the presence of pea roots, the oospores
will germinate and eventually swimming spores (zoospores) will be formed that can infect
pea roots. Infection may occur at any stage of plant growth. Plants are most at risk when
soil is saturated for a long period of time. Symptoms appear as black lesions on the
roots. The pathogen infects the cortex (outer portion) of the root; therefore, when plants
are pulled from the soil, the cortex may slough off, leaving only a small strand of
vascular tissue intact. Minimizing soil compaction will help manage the disease. Planting
oat as a pre-crop has also been shown to reduce disease severity.
Sclerotinia stem rot can infect field pea. Symptoms of the disease include a white,
frothy, fungal growth found on dead or decaying tissue. The fungal growth can develop into
hard black bodies (sclerotia) found inside the stem which can cause premature ripening of
the plant. Typically, long vine varieties having normal leaf arrangement are more
susceptible to sclerotinia, for they tend to lodge after flowering, forming a dense canopy
close to the soil surface and increasing the risk of infection. Generally, semi-leafless
pea that has good standibilty will avoid any serious sclerotinia infections. Infection
risk increases if field pea is planted close in rotation with broadleaf crops such as
sunflower, dry edible beans, canola, mustard or crambe.
Powdery mildew is an economic disease with late-planted field pea. The disease
overwinters on plant residue. Powdery mildew infection usually does not occur until
mid-summer. Yield loss typically doesn't occur unless the infection occurs prior to or
during early pod set. Research indicates that planting field pea beyond mid-May will
result in plants more susceptible to powdery mildew. Powdery mildew will cause a white
"powdery" spot on the lower leaves and stems. Wet or heavy dew conditions help
to spread the disease to upper leaves, flowers and pods. Severely infected plants will not
mature normally. In most instances, infected plants stay green while healthy plants mature
and ripen normally. This will result in harvest moisture problems at harvest and decreased
seed yield. The combination of planting early and use of tolerant varieties will aid in
reducing risk with this disease.
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There are a few insects that are of economic importance in field pea. Aphids that
infest peas are small, about � inch long, and light green in color. Aphids do not
overwinter in North Dakota and are often blown in from southern states in early summer.
Populations usually increase as the summer progresses. Aphids usually don't reach economic
importance in field pea. Aphids will pierce the plant tissue and suck plant juices,
causing the plant to weaken, especially under drought stress. There are no threshold
populations developed for aphids in field pea. Aphid populations are usually kept low by
heavy rains or by beneficial insects such as lace wings or the lady bird beetle.
The lygus bug or "tarnished plant bug" has the potential of being the most
serious insect pest in field pea. Lygus bugs feed preferentially on meristematic tissue or
developing reproductive tissue. The effect of Lygus feeding is shriveled seed. "Chalk
spot" is a damage consideration in field pea. Chalk spot is a chalky white spot which
may appear on the cotyledons of some legumes. It is considered as damage mainly because it
severely affects the appearance of the seed, lowering the grade and marketability. In 1996
and 2002, chalk spot was a concern in the North Dakota pea crop. Chalk spot damage to some
pea samples was as high as 27 percent; however, it could not be documented in all samples
that it was the lygus bug that caused the damage. The other probable cause was that the
pea was harvested at too high moisture. Peas harvested at high moisture are susceptible to
bruising as they are harvested or handled roughly, causing damage similar to chalk spot.
Grasshoppers are usually not a major problem in pea. Pea is not typically a preferred
host, but grasshoppers can cause damage to field pea, especially to pea that is in the
flower to pod-filling stages.
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Harvest management is especially important if field pea is to be marketed as human food
or as seed. Growers should have a goal of producing high-quality peas to receive a premium
price for their crop in the human food or seed markets. If quality problems exist,
including bleached, split, cracked or earth-tagged (dirt attached to seed that cannot be
removed) seed, the livestock feed market will likely be the only option. The following
suggestions will help growers maintain a high-quality crop during harvest and storage.
Field pea may be swathed before combining or straight (direct) combined. Peas are
normally swathed to preserve quality if there is uneven crop maturity or heavy weed
pressure present. If green-cotyledon pea harvest is delayed, bleaching may occur. Bleaching
is caused by rainfall at maturity, high humidity, bright sunshine and warm temperatures.
If green peas are swathed, timely harvest is essential, for green pea will be more
susceptible to bleaching in the swath than if left standing.
When swathing peas, the seed needs to be at physiological maturity. At this stage of
growth, the majority of pods should have turned from green to a yellow color. The crop
matures from the bottom pods upward. Swathing will normally result in increased harvest
losses, but swather modifications make the procedure easier and will reduce harvest loss.
Vine-lifters enable producers to get under the pea vines and lift them over the cutting
knife. Many growers use a pickup reel as well. Peas should be swathed in the early morning
or late afternoon when the pods are tough to reduce shattering losses. Combining should
not be delayed after swathing, because pea swaths are susceptible to movement by wind.
Straight combining is possible, depending on pea cultivar and harvest equipment. Many
short to medium-vine and semi-leafless pea cultivars have characteristics that allow
straight harvesting compared to cultivars with indeterminate and prostrate-vine growth. For
example, semi-leafless pea have a more open canopy, remain erect longer and dry down more
rapidly after a rain or heavy dew than indeterminate long-vine type.
The first choice for direct harvest of short to medium-vine and semi-leafless pea
varieties is a combine header with a floating cutter bar or flex head. Also, attachments
such as lifter guards and pickup reels reduce losses and improve harvest efficiency.
Direct harvesting of weak and prostrate-vine cultivars is most efficient with an aggressive
pickup attachment and a lead coulter on a standard combine.
Field peas should be combined with seed moisture of 14 to 20 percent. At this moisture
range, the seeds are firm and no longer penetrable with a thumbnail. Harvest should occur
during humid conditions to minimize seed shatter. However, pea vines must be dry or
harvest will be extremely slow and difficult. Seed that is too dry will be susceptible to
seedcoat breakage or peeling.
Correct combine settings and operation are important to maintain seed quality. Reel
speed should be slow to minimize seed shatter. Low cylinder speeds, normally 350 to 600
rpm, should be used to minimize seed cracking or splitting. Initial concave settings of
0.6 inch clearance at the front and 0.2 inch at the rear are suggested. Adjust combine
settings as crop and weather conditions change.
Combine and portable augers should be operated at full capacity and low speeds to
reduce pea seed damage. Alternative seed handling equipment such as belt conveyors should
be considered for handling seed intended for seed or the human food market. Minimize the
number of times seed is handled. Also, don't handle peas during cold temperatures as
potential for seed damage dramatically increases.
Green weed seeds or foreign material should be cleaned from the crop before storage to
avoid spoilage and fewer market opportunities. Seed should be stored at 14 to 16 percent
moisture. Seed that is marketed in the human edible market often requires moisture below
14 percent. Pea seed at 18 percent moisture can be stored for 20 weeks at 68 degrees F,
but only for four weeks at 77 degrees F. An aeration system should be present in the
storage facility. The recommended airflow volume for bins is about one to two cubic feet
of air per bushel per minute. Warm seed should be immediately cooled after binning, even
if seed moisture is low.
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Primary field pea market opportunities are for livestock feed, seed and human food.
Markets are readily available with minimal quality restrictions for peas sold as livestock
feed. Prices received for feed peas should be considered base prices. Opportunities exist
to enhance the value of feed peas by using the commodity as an on-farm livestock feed
source. Consult the NDSU Extension Service circular EB-76, Feeding Peas to Livestock.
Premium prices are associated with the human food and seed markets. Selling peas in the
premium markets is a greater challenge than marketing a traditional small grain crop.
Premium pea markets are normally limited and require a more aggressive approach by the
grower. Pea markets should be identified before peas are produced to optimize the ability
to harvest a crop that will meet market standards. For example, when marketing food-grade
peas, numerous factors that affect market grade include market class (e.g. green or yellow
cotyledon, specialty types), seed size and shape, splitting potential, harvest moisture,
seed handling techniques during harvest and storage and seed damage factors (e.g. bleach,
cracked seed coats, splits, shriveled seed, earth tag, chalk spot, etc.).
After harvest, the crop needs to be graded to determine what markets are options for
the grower.
A representative two-pound sample may be sent to the Federal Grain Inspection
Service: USDAGIPSA FGIS, P.O. Box 13427, Grand Forks, ND 582083427. Peas grading U.S. No.1
or 2 qualify for the human food market.
It is important to keep abreast of current markets by using sources such as written or
electronic agricultural publications. Due to limited market opportunities for human food
grade peas, make sure local, state or regional buyers are aware of the quality and
quantity of crop you have available for sale. An additional market option for human food
grade peas is the PL480 program, a U.S. government program designed to distribute surplus
commodities to aid developing nations.
A listing of potential buyers and market opportunities is available from the
North Dakota Dry Pea and Lentil Association (4023 State Street, Bismarck, ND 58501;
telephone 701-222-0128) or NDSU Extension Service offices.
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For more information on this and other topics, see:
www.ag.ndsu.nodak.edu
A-1166(Revised), March 2003
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