Prepared June, 2000
About 95% of Idaho green peas are produced in Nez Perce and Lewis County, with the remainder in Latah County.
All green peas produced in Idaho are for the frozen pea market. Green pea varieties for the frozen market differ from canner and dry pea varieties in several characteristics. Green peas are typically higher in quality, possess a wrinkled seed coat, darker green due to color in the seed coat, and smaller in size. Quality green peas must also possess tender skin, high sugar content, and be free from decay, scald, and injury caused by heat, insects and disease.
Green peas are an important crop in Northern Idaho because they provide growers with greater revenue than alternative dry pea or spring grain crops. As a rotation crop with winter cereals, green peas break the disease and weed cycle, conserve soil moisture relative to other rotational crops, improve soil fertility by fixing nitrogen, and increase yields in the next crop planted.
The climate conditions accompanying green pea production in northern Idaho includes mild, wet winters and springs, hot dry summer days, and cool summer nights. Green peas are grown on non-irrigated land that receives 14 to 28 inches of annual precipitation, primarily during winter and early spring.
Green peas are grown following winter wheat or spring barley. Cereal stubble that is fall plowed or chiseled is cultivated in the spring for weed control followed by herbicide incorporation. The crop is then seeded and the ground harrowed and rolled.
Optimal seeding rates vary with the green pea variety, but usually average 180 pounds per acre. Green peas are drilled in rows 6 to 7 inches apart. Green peas are relatively inefficient at using stored soil moisture and rely on spring and summer rains for most of their growth cycle. Depending on the variety, green peas start flowering after a specific number of nodes are produced.
The green pea processor contracts with local producers to grow green peas. The processor prescribes operations such as planting date, scouting for insects and weeds, insect control, and harvest of the crop. Growers in turn perform operations as specified in the contract, usually planting, weed control, and harvest of the crop.
Pea plantings are scheduled over an eight-week period from mid-March to mid-May. They begin at lower elevations when soil temperatures reach 50°F, and progress to mid and high elevations (4000 ft) as spring temperatures increase. Plantings are scheduled on the basis of heat units, taking into account differences in site elevation, slope and aspect and cultivar maturity. The processor utilizes about eight cultivars that range in maturity from early to late to extend the harvest season to achieve efficient harvest of all planted pea acreage. Prescribed cultivars include Samish (66 day maturity), Sundance (70 day maturity), and Scamp (61 day maturity). Each season the number of heat units above 40°F required to bring a specified cultivar to maturity is calculated. From past experience with cultivar maturity, heat units and weather records, processors can schedule fields for harvest to provide a uniform volume of peas for processing over a 40 to 50 day harvest season.
Scheduled planting avoids exceeding the capacity of the harvesters and processing plant to effectively process peas. Harvested green peas must be delivered to the processing plant within two hours to avoid quality losses such as off-flavors and physical damage. Thus, all green pea acreage must be located within one hour trucking distance to the plant. Peas that are less than optimally mature or processing that is not timely leads to quality and price reductions or unmarketable peas.
The processor specifies harvest dates based on the tenderometer reading, number of fields approaching maturity, and prevailing and forecasted weather conditions. Harvest date is also influenced by the quality standards that must be met. Tenderometers are devices that measure the toughness of the pea seed coat and firmness of the pulp. This measurement provides rapid assessment of pea maturity.
Green peas are one of the most perishable vegetables. They pass rapidly through the optimum stage of maturity during hot, dry and windy weather. A delay of 1 to 2 days in harvest may result in greater yields but can cause a 90% reduction in No. 2 and No. 3 peas. Green pea harvest begins in June in lower elevation fields and proceeds to higher elevation fields, usually ending in early August. The optimum harvest time is when pods are filled and the peas are still soft and relatively immature. Generally, those areas with higher precipitation produce higher pea yields. Pea harvesters strip the pods from the plants, and then remove the peas from the pods. About 5% yield loss occurs during the mechanical harvest. As green peas increase in size beyond No. 2. and No. 3., they decrease in quality by becoming less succulent. Because of their smaller size, No. 1 peas pass through the combine screens and are not retained. The processing plant operates as the green peas are delivered after harvest.
Integrated Pest Management:
Several cultural practices in green pea production contribute to reduced pesticide input and suppressed pest populations. All growers practice crop rotation to reduce diseases, insects, and weeds in the following crop. All pea fields are scouted for weeds and insects to determine the economic thresholds for chemical control.
Pea growers and beekeepers have developed several guidelines to help reduce pesticide injury to pollinating bees. Beehives are appropriately located and pesticide applications are made to minimize bee injury. Beekeepers are contacted before pesticides are applied and bees are confined or removed from the application site when appropriate. Most pesticides toxic to bees are applied during the early morning or late evening when bees are less active. Growers will not apply pesticides if temperature inversions exist.
The pea weevil is a pest of green peas that warrants spot control every year. Adult weevils over-winter in fencerows, in timbered areas adjacent to fields, and on roadside vegetation. Larvae are the most damaging, and burrow directly through the pod and consume the pea seed. The economic threshold for initiating pea weevil control is reached when more than 2 weevils per 25 sweeps are found or weevils are caught over a large area. Insecticides must be applied to prevent the females from laying eggs because once eggs are laid on the pea pods, all treatments are ineffective.
Phosmet (Imidan 70W) -- Phosmet is an important insecticide for pea weevil control. An estimated 5-10% of the pea fields are treated each year for pea weevil. Generally applied once per year at a rate of 0.7 pounds active ingredient per acre. PHI is 7 days.
Pea Leaf Weevil
The pea leaf weevil (PLW) adult is a serious pest in green peas and causes economic loss in most years. Severely infested green pea fields may suffer up to 80% crop loss. Most of the damage occurs in spring on peas in the seedling stage. Early adults feeding on seedlings cause scalloped leaf edges and damaged terminal buds. Severe foraging may cause heavy leaf damage, destruction of the terminal buds, and ultimate destruction of the plant. Weather conditions during the growing season have a strong influence on the damage caused by the PLW. PLW are most active during warm, sunny weather. Damage by the PLW can be localized or cover large areas.
Phosmet (Imidan 70 W) -- Phosmet is an extremely important insecticide for PLW control. An estimated 25-50% of the pea fields are treated each year with phosmet to control pea leaf weevil. Generally applied once per year at a rate of 0.75 pound active ingredient per acre. PHI is 7 days.
Natural predators are usually not present in significant numbers to reduce PLW populations below economically damaging levels.
Pea Aphid(Acyrthosiphon pisum)
Cowpea Aphid (Aphis craccivora)
The pea aphid and the cowpea aphid are a serious pest of green peas. If not controlled, feeding by aphids can destroy up to 100% of developing plants. They are able to multiply quickly so a moderate infestation can become a damaging population in less than a week. Aphids damage green peas by sucking sap from leaves, stems, blossoms and pods. Plants heavily fed upon are stunted and produce fewer and smaller pods and seeds. Smaller plants may die from aphid feeding. Aphid predators, such as the larvae of lady bugs, are usually not present in high enough numbers, and typically lag behind the development of aphid populations.
Aphids also may transmit viruses such as pea enation mosaic virus, pea streak virus, and pea leaf roll virus. Aphids acquire the viruses while over-wintering in alfalfa and other crops that host the viruses. Once the aphid acquires one or more of these viruses, it retains the ability to transmit the viruses for about 24 hours. Once infected, symptoms develop in about 7 to 10 days. Symptoms of virus infection include mottling, crinkling of the upper leaves, enations and stunting. Pods may become distorted, and produce few or no peas.
Dimethoate (Dimethoate) -- Dimethoate is an extremely important insecticide for aphid control. About 70-100% of pea acreage receives one application, with another 10-30% receiving a second application to control resurgent aphid populations. Typically applied at a rate of 0.17 pound active ingredient per acre. Usually applied at 1/3 to 1/2 the labeled rate to allow for a second application, if needed. PHI is 14 days.
Natural predators are usually not present in significant numbers to reduce aphid populations below economically damaging levels.
Diseases can seriously reduce the yield and quality of green peas. Planting when soil temperatures reach 50°F will reduce pea seed exposure to cool soil temperatures and will usually reduce disease problems caused by Pythium species. Several pathogens that cause diseases of peas persist in soil and crop residue for years, even in the absence of peas or other host crops. Diseases of green peas occur under a wide range of cool, warm, wet, and dry soil conditions. To minimize impacts from diseases, all green pea seed is pre-plant treated with fungicides.
Seed Rots and Seedling Blights
Seed rots and blights are a serious disease of green peas, and are caused by soilborne and seedborne fungi that reduce emergence and stand. Pythium species are the major cause of seed rot, but Aphanomyces euteiches, Fusarium solani, and Rhizictonia solani also contribute to this problem. Seed typically is infected shortly after planting, and may fail to emerge or damp-off soon after emergence.
Root rot is a serious disease affecting green pea production. Green peas typically survive and perform in the production region with 1/3 or more of their root system destroyed by root rotting fungi. Root rot is caused by several fungi, but is caused primarily by Aphanomyces euteiches (early spring) or Fusarium solani f. sp. pisi (early summer), and several species of Pythium. Favorable conditions for root rot include warm, wet or dry soils, excessive compaction, and low fertility. Aphanomyces favors wet compacted soil. While primarily soil-borne, these fungi are also spread in the residue and dust of contaminated seed lots. Symptoms of root rot include stunted, nonvigorous plants often yellowing from the base upward. Because of the longevity of these fungal pathogens on plant hosts and debris, rotations with non-host crops do not appreciably reduce the soil inoculum.
Captan (Captan 400) -- Captan is considered an important fungicide to control diseases. Captan is applied as a seed treatment to all green pea seed at a rate of 2.5 fluid ounces per cwt of seed.
Metalaxyl (Allegiance FL) – Metalaxyl is applied once per year to all green pea seed at a rate of 0.4 fluid ounces per cwt of seed.
No resistant cultivars are available but vigorous cultivars, crop rotations with wheat or barley, and the use of seed treatments provides moderate protection against seed diseases. Since root rot pathogens remain viable in the soil for several years, crop rotations with non-host crops will not eliminate the diseases. Cultivation of green peas no more frequently than every three years may reduce the severity of these diseases, but will not protect green peas from becoming re-infected.
Pea Enation Mosaic Virus
There are at least 27 different viruses that have been identified in green peas. Of these, pea enation mosaic virus (PEMV) is the major pathogen that can cause significant damage under favorable conditions. PEMV survives from year to year in alternate crops such alfalfa, chickpea, clover, pea, vetch and some weed species. PEMV is not seedborne and can only be transmitted by aphids. The principle vector is pea aphid and the green peach aphid, which can aquire the viruses after feeding on infected host plants. Flights of aphids in the spring and early summer from infected hosts spread the viruses to green peas. Symptoms of PEMV include mottling, crinkling at the top of the plant, stunting, and tissue outgrowth on pods and leaves. Pods may become distorted, and produce few or no marketable peas.
The extent of damage caused by PEMV varies from year to year and by geographical regions. Epidemics have occurred with only trace populations of aphids on peas. Climatological and biological factors that trigger epidemics are not yet understood. In average years, damage is usually minimal, but about one in five years viral infections reach damaging levels and cause severe economic loss. In the 1983, PEMV was epidemic in peas and caused severe damage. In these instances, yields losses reached 50% in localized areas.
Resistant pea varieties are continually being tested and many are now available for PEMV. Controlling aphids with systemic aphicides such as dimethoate have been only partial successful in reducing the field spread of viruses. Overwintering aphids feed on infected host crops and spread the virus to peas before insecticides are applied for aphid control. Aphicides do, however, help stop the spread of secondary infection to peas.
Grass and broadleaf weeds are a very serious problem in green pea production. Typical troublesome weeds include wild oats, various mustards, pigweed, common lambsquarters, nightshade, Canada thistle, prickly lettuce, pineapple weed, field pennycress and mayweed chamomile. Green peas are poor competitors against weeds and require a weed control program. An ineffective weed control program can cause a 100% green pea yield loss. Weeds can also contribute exudate at harvest that can stain or contaminate the peas. Contaminated peas are considered inferior in quality. Weeds also interfere mechanically with green pea harvest.
Imazethapyr (Pursuit) -- Imazethapyr is the most widely used herbicide to control broadleaf weeds. Applied to about 60% of the green pea acres once per year at a rate of 0.031-0.047 pound active ingredient per acre. PHI is 60 days. Frequently applied pre-plant incorporated in combination with triallate to control wild oats.
Metribuzin (Sencor DF 75%) -- Metribuzin is applied to about 30% of the acres once per year at a rate of 0.2 pound active ingredient per acre. PHI is 50 days. Metribuzin is most commonly applied pre-emergence to control mayweed and common lambsquarters.
Bentazon (Basagran) -- Bentazon is applied to about 15% of green pea acres for post-emergence weed control. Applied once per year at a rate of 0.75 pound active ingredient per acre. PHI is 30 days. Bentazon provides fair control of pineapple weed and mayweed. Bentazon is applied to entire fields, but is especially useful on small sections of fields for controlling weeds in lower, wet areas without causing injury to peas. It is estimated that 20% of the growers will use bentazon on portions of their green pea acreage.
Glyphosate (Roundup) – Applied to about 50% of the acreage before cultivation to control weeds such as Canada thistle, mayweed, and grasses. Usually applied at a rate of 0.75 pound active ingredient per acre once per year. PHI is 14 days. Glyphosate is also used as a spot treatment or broadcast to control escaped weeds such as Canada thistle. Especially useful in low, wet areas of fields where troublesome weeds may persist.
Cultivation removes weeds before planting, but is not useful during the growing season because of the narrow row spacing.
Annual Grass Weeds
Triallate (Far Go) -- Applied to 75% of the acres once per year at a rate of 1.25 pounds active ingredient per acre. Currently the most widely used herbicide for wild oat control. Future use may decline as growers substitute quizalofop for triallate. Frequently applied in combination with imazethapyr (Pursuit) for broadleaf control.
Quizalofop P-ethyl (Assure II) -- Applied to about 15% of the acres post-emergence to control perennial and annual grass weeds such as wild oats, volunteer cereals, and other weeds. Typically applied at a rate of 0.06 pound active ingredient per acre. Not more than 0.09 pound active ingredient per acre can be applied per year. PHI is 30 days. Quizalofop has the advantage of controlling weeds on an "as needed basis." Use of quizalofop is predicted to increase to about 50% in the next few years. Growers not using pre-plant application of triallate, apply quizalofop post-emergence.
Rick Dudley, Twin City Foods, Lewiston, ID 83501
Samuel J. Fuchs, Extension Support Scientist I
College of Agriculture, University of Idaho, Moscow, Idaho
Ronda Hirnyck, Pesticide Program Coordinator
University of Idaho - Boise Center
Ronda Hirnyck, Pesticide Program Coordinator
University of Idaho—Boise Center
800 Park Blvd., Suite 200
Boise, ID 83712
(208) 364-4046 phone
(208) 364-4035 fax
Database and web development by the NSF Center for Integrated Pest Managment located at North Carolina State University. All materials may be used freely with credit to the USDA.