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Peas -- Western Oregon

Pisum sativum

Last revised January 3, 2003

Seeding o Fertilizers o Harvesting, Handling, Storage o Pest Control: Diseases, Insects, Weeds


Peas in western Oregon are grown in the Willamette Valley. Production may be irrigated or non-irrigated. The non-irrigated production area is generally in the Cascade foothills around Silverton.

Although peas have been grown in western Oregon for canning, due to market conditions and processor requirements, all peas in western Oregon are now grown for freezing. Freezing and canning varieties differ in a number of characteristics. In general, freezers are darker green due to the presence of green color in the seed coat. Raw seed may either be wrinkled (freezers) or smooth (canners). Varieties may be also classified by sieve size, with small-sieve peas being important for freezing and becoming more popular in general. The development of dual-purpose varieties are making these distinctions less important.

More recently, modified-leaf varieties have become available. The afila type is a semi-leafless mutant where the leaflets have been converted to tendrils. Stipule leaves are still present. This plant habit makes possible an open plant structure that favors good aeration, a better growth habit, better light penetration, and improved color. A uniform, intense green color is especially important in freezer peas. The upright plant habit also improves harvest recovery and efficiency.

Scheduling plantings for orderly harvest is accomplished by the use of the accumulated heat unit (AHU) system. This is defined as the accumulated difference between the base temperature for crop growth and the mean of the daily maximum and minimum air temperatures. The AHU system information combined with selection of appropriate early and main season varieties, and with field selection based on elevation has been effective in pea production scheduling. Using a 40 F base, early varieties currently used require 1200 to 1300 heat units, mid-season varieties 1400 to 1500 heat units and late varieties 1600 to 1700 heat units to reach a 100 tenderometer maturity in the Willamette Valley.


VARIETIES

Processing: Processors will specify varieties for each planting period.

Some varieties grown in western Oregon are: Venus, Kodiak, Trident, Midget (small-seeded type), Signet, Mars, Bolero, and Dark Seeded Perfection types.

Fresh market: early: Oregon Pioneer; main season: Oregon Pioneer for early plantings, Oregon Trail for mid and late season plantings. Both are pea enation mosaic virus resistant, with Oregon Trail also being powdery mildew resistant. Both have some tolerance to red clover vein mosaic. These are replacements for the variety Corvallis. For trial: Charo, Renown, Sundance.


SOIL AND LAND PREPARATION

It is important to choose a field with uniform fertility, soil type, slope, and drainage to get a uniform pea crop. The best soils are silt loams, sandy loams, or clay loams.

Peas need a good supply of available soil moisture, but yields may be reduced by over-irrigating as well as under-irrigating. Peas grown on wet soils develop shallow root systems which cannot supply the plant's water requirements when the soil dries out later in the season. Root rot is often a problem in wet soils.

Determine corrective lime and fertilizer needs by a soil test. Adjust pH to 6.5 or higher for maximum yields.

Land should be plowed, harrowed, and a cultipacker used lightly to ensure a firm seed-bed. The land should be level in order to make harvesting more efficient. Care must be exercised in avoiding subsurface compaction since this contributes to limited aeration and rooting and predisposes roots to a number of root pathogens.

Peas are tolerant of cool soil temperatures, but sensitive to flooded or excessively wet soils associated with early spring plantings in western Oregon. Germination will occur at 40 to 85 F, ideally 50-75 F.


SCHEDULING PLANTINGS

Plantings may be made as soon as the soil can be worked in the spring. Peas in western Oregon are planted from late February through mid-May. Enation-resistant varieties may be planted throughout the entire planting season. Terminate the use of enation susceptible varieties by April 1 (see variety list and Disease Control section).

Processing peas are scheduled on the basis of heat units. Planting and harvest schedules are established by the processing company.

Fresh market peas and edible pod peas may be scheduled on the basis of heat units and by picking requirements for given plantings. In general, April plantings will require about 70 days to harvest, May plantings about 60 days and June plantings about 55 days. Plantings should be about 2 weeks apart in April and early May and about 1 week apart from mid-May on. Plant the amount of area would be picked over that period of time.


SEEDING

Pea seed numbers approximately 2000 per lb for standard varieties, to 3000 per lb for small seeded varieties. For processing, drill seed at a uniform depth of l.5-2 inches into moisture, dropping 3 to 6 seeds per foot of row with rows 6-8 inches apart. Aim for a plant population of 350,000 for standard varieties to 480,000 plants per acre for small seeded varieties (these tend to have lower emergence).

Avoid excessive overlaps and double planting along the edges of the field. This may cause uneven colored peas and lack of uniformity at harvest. The new small-seeded varieties must be planted shallow in order to obtain the best stands. These peas are less vigorous than the standard types, and for that reason they need to be planted where moisture is close to the surface, and in the more fertile fields.

Providing moisture is adequate and not excessive, a light rolling may be advantageous. Heavy rolling or packing is likely to reduce root growth, fertilizer uptake and pea root nodulation, and to increase the number of plants affected by root rot.

Inoculate with Rhizobium bacterium in a planter box treatment when planting on soils not previously planted to peas.

New research indicates that stand and seedling vigor can be greatly reduced by the presence of hollow heart (or cavitation) in the seed. This is a physiological disorder believed to be aggravated by premature combining or swathing of the seed crop. This disorder can affect seed quality of all varieties from all seed sources. Differences in severity by variety and seed source can be large. The range of seed affected was from 5% to 78% with a mean incidence of 33% in a 1986 seed sampling study, and 4% to 75% with a mean incidence of 30% in a 1985 study.


FERTILIZER

Good management practices are essential if optimum fertilizer responses are to be realized. These practices include use of recommended pea varieties, selection of adapted soils, weed control, disease and insect control, good seed bed preparation, proper seeding methods, and timely harvest.

Because of the influence of soil type, climatic conditions, and cultural practices, crop response from fertilizer may not always be accurately predicted. Soil test results, field experience, and knowledge of specific crop requirements help determine the nutrients needed and the rate of application.

The fertilizer application for vegetable crops should insure adequate levels of all nutrients. Optimum fertilization is essential for top quality and yields.

Recommended soil sampling procedures should be followed in order to estimate fertilizer needs. The Oregon State University Extension Service agent in your county can provide you with soil sampling instructions and soil sample bags and information sheets.

NITROGEN (N)

Rates of 20 to 30 lb N/A banded with P and possibly K at planting time are suggested. Peas have the capacity to fix atmospheric nitrogen, and have been shown to use this nitrogen more effectively than applied N. The application of N at rates higher than those indicated may be detrimental to nitrogen fixation by the plant and yields.

Information on the application of N is given below in the sections on P and K.

INOCULATION

Pea seed should be inoculated immediately before seeding to insure an adequate supply of nitrogen-fixing bacteria when planting in soils not having been used for pea production previously. A fresh, effective, live culture of the correct strain of Rhizobium should be used.

PHOSPHORUS (P)

Phosphorus is essential for vigorous early growth of seedlings. Preferably P, N, and, where required, up to 60 lb K2O/A should be applied in a band 2 inches to the side and 2 inches below the seed at planting time.

When banding equipment is not available 20 to 30 lb N/A and 40 to 80 lb P2O5/A can be drilled with the seed. Additional P2O5 and K2O, when required, can be broadcast and plowed down prior to planting.

           If the soil test*            Apply this amount of
          for P reads (ppm):          phosphate (P2O5) (lb/A):

                0 - 15                       120 - 150
               15 - 60                        80 - 120
               over 60                        40 -  80
*Assumes extraction procedures similar to those used by the OSU Central Analytical Laboratory. Specific information on soil test procedures is available from the Dept. of Crop and Soil Science.

POTASSIUM (K)

Potassium should be applied and plowed down before planting or banded at planting time as described in the above section on P.

Potassium should not be included with N and P when fertilizer is drilled with the seed. In a 2" x 2" band application of N, P, and K the K rate should not exceed 60 lb K2O per acre. Additional K, where required, should be broadcast and plowed down prior to planting.

Seedling injury from banded fertilizers tends to be more serious:

- in drier soils
- in coarse textured, sandy soils
- where fertilizer band is close to seed.

Phosphorus fertilizers are less injurious to seedlings than N and K fertilizers.

                  If the soil test*         Apply this amount of
                 for K reads (ppm):              K2O (lb/A):
                      0 - 100                     90 - 120
                     75 - 150                     60 -  90
                    150 - 200                     40 -  60
*Assumes extraction procedures similar to those used by the OSU Central Analytical Laboratory. Specific information on soil test procedures is available from the Dept. of Crop and Soil Science.

SULFUR (S)

Plants absorb S in the form of sulfate. Fertilizer materials supply S in the form of sulfate and elemental S. Elemental S must convert to sulfate in the soil before the S becomes available to plants. The conversion of elemental S to sulfate is usually rapid for fine ground (less than 40 mesh) material in warm moist soil.

Sulfur in the sulfate form can be applied at planting time. Some S fertilizer materials such as elemental S and ammonium sulfate have an acidifying effect on soil.

Sulfur is sometimes contained in fertilizers used to supply other nutrients such as N, P, and K, but may not be present in sufficient quantity.

Responses to S fertilization may not occur for a period of at least 4 or 5 years on "red hill" soils that have a history of high S fertilization. These soils have a comparatively high ability to adsorb S and frequently have a history of high S fertilization through the use of S-containing fertilizer such as ammonium sulfate.

The S requirements of peas can be provided by:

  1. The application of 20-30 lb S/A in the form of sulfate at or prior to seeding.
  2. Applying 30-40 lb S/A as fine ground (finer than 40 mesh) elemental S the preceding year.
  3. Applying coarser ground elemental S at higher rates and less frequently.
MAGNESIUM (Mg)

When the soil test value is below 0.5 meq Mg/100g or when calcium (Ca) is 10 times more than the Mg apply 10 to 15 lb Mg/A banded at planting.

Magnesium can also be supplied in dolomite which is a liming material and reduces soil acidity to about the same degree as ground limestone. Dolomite should be mixed into the seed bed at least several weeks in advance of seeding and preferably during the preceding year. An application of dolomite is effective for several years.

OTHER NUTRIENTS

Responses of peas to nutrients other than those discussed in this guide have not been observed in western Oregon. Peas have a comparatively low requirement for boron, which should never be included in fertilizer banded with peas.

LIME

Peas are fairly sensitive to soil acidity and are responsive to liming of acid soils.

Lime application are suggested when the soil pH is 6.0 or below, or when calcium (Ca) levels are below 5 meq Ca/100g of soil.

                If the SMP Buffer*           Apply this amount
               test for lime reads:           of lime (T/A):
                    below 5.5                         6
                    5.5 - 5.7                     5 - 6
                    5.7 - 5.9                     4 - 5
                    5.9 - 6.1                     3 - 4
                    6.1 - 6.3                     2 - 3
                    6.3 - 6.5                     1 - 2
                    over 6.5                          0
*Assumes extraction procedures similar to those used by the OSU Central Analytical Laboratory. Specific information on soil test procedures is available from the Dept. of Crop and Soil Science. The suggested liming rate is based on 100 score lime.

Apply lime at least several weeks before seeding and preferably the preceding year and mix with the surface 5 to 6 inches of soil.

A lime application is effective over several years.

Some soils may have a fairly high SMP buffer value (over 6.5) and a low pH (below 5.5). This condition can be caused by the application of acidifying fertilizer. In this case the low pH value is temporary and the pH of the soil will increase as the fertilizer completes its reaction with the soil. This temporary "active" acidity from fertilizer is encountered following recent applications of most N fertilizer materials. Acidifying fertilizers also have a long term acidifying effect on soil which is cumulative and leads to lower OSU SMP buffer readings.

Sandy soils to which fertilizers have not been recently applied sometimes record low pH and high SMP buffer values. In such cases, a light application of l to 2 T lime/A should suffice to neutralize soil acidity.

For acid soils low in Mg (less than 0.8 meq Mg/100g of soil) 1 T/A dolomite lime can be used as a Mg source. Dolomite and ground limestone have about the same ability to neutralize soil acidity.

Fertilizer Guide #3, "Liming Materials for Oregon," which is available from your local OSU Extension Office, provides additional information on lime.


IRRIGATION

Peas are produced successfully with or without irrigation depending on the area of production and cropping practices. Where center pivot systems are available, peas may be conveniently and economically irrigated, taking advantage of the large response peas exhibit to irrigation, however timing is important.

1. Do not irrigate peas before flowering unless the ground is very dry and germination would not otherwise occur, or the crop is severely wilted. Irrigation at this time may actually decrease yield.

2. Irrigate when flowers are first opening. This is when peas are most responsive to irrigation because root growth ceases and demand for moisture is high.

3. Peas do not generally respond to irrigation after flower petals begin to fall, and irrigation at this stage may increase disease incidence.


HARVESTING, HANDLING, AND STORAGE

In the Willamette Valley, pea harvest for processing may begin about June 1 and extend to September 30. The prime harvest period is from June 7 to September 20.

The processor determines time of harvest according to tenderometer reading, the number of other fields ready for harvest, weather, soil conditions, and the processor`s need for quality. Generally, yields of shelled peas increase with increasing maturity, but quality decreases.

With mobile viners the crop is cut and swathed into windrows, threshed out by the mobile viners following swathers. Peas must be delivered to the processing plant soon after harvest, especially when the weather is hot, to avoid off-flavors. With the new pod stripping harvesters, no swathing is needed.

STORAGE (Quoted or modified from USDA Ag. Handbook 66 and other sources)

Green peas tend to lose part of their sugar content, on which much of their flavor depends, unless they are promptly cooled to near 32 F, relative humidity 90-95%, after picking. Hydrocooling is the preferred method of precooling. Peas packed in baskets can be hydrocooled from 70 to 34 F in about 12 minutes when the water temperature is 32 F. Vacuum cooling also is possible, but the peas must be prewet to obtain cooling similar to that by hydrocooling. After precooling, peas should be packed with crushed ice (top ice) to maintain freshness and turgidity. Adequate use of top ice provides the required high humidity (95 %) to prevent wilting. The ideal holding temperature at 32 F. Peas cannot be expected to keep in salable condition for more than 1 to 2 weeks even at 32 F unless packed in crushed ice. With ice, the storage period may be extended perhaps a week. Peas keep better unshelled than shelled.

Research in England showed that the edible quality of green peas was maintained better when the peas were held in a modified atmosphere of 5 to 7 % carbon dioxide at 32 than in air for 20 days.


PACKAGING

Fresh market peas are hand harvested and the pods are commonly packaged in 30 to 32-lb bushel wirebound crates, or 28 to 30-lb bushel baskets.


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