Asparagus Information Bulletin
Information Bulletin 202
COOPERATIVE EXTENSION NEW YORK STATE CORNELL UNIVERSITY
R.F. Sandsted, D.A. Wilcox, T.A. Zitter, and A.A. Muka
Cornell University, Ithaca, NY
Asparagus is a popular vegetable that can provide growers with an early-season fresh commodity. Commercial outlets include U-pick operations, roadside markets, farm markets, grocery stores, and wholesale distributors. At the present time there are no processors of asparagus in New York, but this outlet is a future possibility.
The demand for this tasty early spring vegetable is good. Consumers are enthusiastic about locally grown fresh asparagus, which is superior in quality to that shipped in from distant production areas. For consumers who are concerned with caloric and sodium intake, asparagus has a low content of both; yet it provides significant amounts of vitamins A and C in the diet. It also provides the vitamins riboflavin, niacin, and thiamin and the minerals iron, phosphorus, and potassium.
Two years are required to establish an asparagus field, but once into production plantings endure from 10 to 20 years.
The USDA Crop Reporting Service estimated the U.S. 1984 planted acreage of fresh market and processing asparagus to be 93,300 acres. By far the leading states in planted acreage were California, Washington, and Michigan, with a total of 85,200 acres. The total acreage for the other states of Illinois, Indiana, Maryland, Minnesota, New Jersey, and Oregon was 8,100 acres. There is considerable acreage in both Canada and Mexico. Planted acreage, excluding home gardens in New York, is estimated at less than 500 acres.
Average yields in California and Washington are between 2,500-3,000 pounds per acre. A long growing season accounts for the high yields in these two states. Average yields in most other states are between 1,000 and 1,500 pounds per acre. Keep in mind that these are average figures and much higher yields do occur.
Because of the small acreage of asparagus in New York, no studies have been made of production costs. Growers in need of this information may obtain a copy of Michigan State Cooperative Extension Bulletin E-1327, Costs of Asparagus Production in Western Michigan, from the Michigan State Cooperative Extension Service, Michigan State University, East Lansing, MI 48824. This bulletin was published in 1979; costs may be somewhat higher now. A column is provided where growers can enter an adjusted cost for their situation. Harvesting and marketing are major costs if labor is hired to harvest, grade, package, and transport the product.
Asparagus (Asparagus officinalis var. altilis L.) is a hardy perennial vegetable native to the seacoasts of Europe and eastern Asia, where it has been cultivated for over 2,000 years. It was a well-known and valued vegetable to both the Greeks and Romans. Early settlers brought asparagus to North America, where it has been grown in home gardens since colonial times. Commercial asparagus production began in this country in the middle of the ninteenth century.
The underground portion of the plant consists of a network of rhizomes, fleshy storage roots, and fibrous roots. The fleshy roots (as well as the spears) are initiated from the rhizomes. Together, the fleshy roots and rhizome make up the crown, which is the perennial portion of the asparagus plant. Fleshy roots serve not only as storage organs for the carbohydrates received from the fern, but also as the site of fibrous root development. Fibrous roots, which live for one or two seasons, function in the absorption of water and nutrients from the soil.
The word asparagus comes from the Greek asparagos, meaning shoot or sprout. Asparagus spears are, in fact, edible shoots that develop on rhizomes when the soil temperature is warm and the water supply is favorable. The spears, if not harvested, develop into ferns 4-6 feet tall. Carbohydrates and other compounds necessary for plant growth and development are produced in the ferns throughout the growing season. These substances are translocated to the fleshy roots, where they are stored and used to produce spears the following spring.
Asparagus plants are dioecious, meaning that male and female flowers are produced on separate plants. The flowers are small, bell shaped, and whitish green. Male flowers are more conspicuous than female flowers. Following pollination of female flowers by bees, a berry, which has one to eight seeds and turns red at maturity, develops. The seeds, which are threshed from the berry when dry, are single, large, black, and generally round with one flattened side. Female plants are somewhat less productive and shorter lived than male plants because of the energy allocated to seed production. Thus, in a given planting of dioecious hybrids or plants from open-pollinated sources, the ratio of male to female plants initially is 50:50. As the age of a planting increases, the ratio of male to female plants increases.
When the soil temperature is below approximately 50° F or the water supply is limiting, crowns become dormant. In the Northeast, cool soil temperatures induce winter dormancy, whereas in tropical or subtropical growing areas, irrigation may be withheld to induce dormancy or special methods are employed to produce the crop without a dormant period. The dormant period preserves the carbohydrates or energy, giving rise to spear production the following season.
Select relatively level fields for asparagus. Much soil erosion can occur on slopes, particularly during the first 2 years after planting, when there is little plant residue in or on the land. During the year of planting, rainwater can concentrate in and flow down the open furrows, where it may wash out the young plants or cover them with soil. Areas known to be subject to late frosts should be avoided. Frost will destroy emerged spears, delay harvest, and reduce yields (fig. 1). Fields should be stone free or nearly so. Select fields with few or no stones, or remove them before planting. Stones may concentrate in the plant rows when the furrows are filled and, in later years, cause spears to be crooked or otherwise damaged. If harvesting is done by cutting the spears below ground, stones greatly interfere with cutting knives. If the furrows are filled in by hand (rakes or hoes), stones can be moved to the area between rows and picked up later, but this is a laborious task.
Fields should be as weed free as possible, particularly free of perennial weeds. Before the days of modern herbicides it was a standard recommendation that fields be tilled or managed to eliminate as many weeds as possible a year ahead of planting the asparagus. This management often included cultivation and (or) cover crops and the addition of lime, if needed. The recommendation still has considerable merit.
Good soil-water drainage is very important because asparagus does not tolerate wet roots. The crop can survive short periods of flooding, but not prolonged waterlogged soil. Sandy loams and loams are best for asparagus. The more sandy the soil, the more likely the plants will suffer from drought stress unless irrigation is available. Asparagus can do well in rather heavy soils, but these soils often have poor drainage and form crusts that can cause damage to emerging spears. The reserve water-holding capacity of the heavier soils can be an advantage if internal soil drainage is good. Do not plant on muck soils because freezing heaves and damages the crowns.
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Field preparation before planting is the same for crowns, transplants, or direct seeding. Subsoiling before plowing deeply is advisable if a compacted plow layer exists. Disk and (or) harrow until reasonably free of clods, but do not overcompact the soil. If the soil test shows a need for lime, it is essential that it be applied during field preparation. There will be no opportunity to plow down or deeply till in lime or fertilizer after the asparagus is planted.
Manure, if free of weed seed, particularly that of perennial weeds, can be incorporated into soil during field preparation.
The choice of varieties has changed little over many years. The open-pollinated Mary and Martha Washington varieties continue to be the predominant ones offered by commerical seed houses. Many seed houses, in fact, offer their own special strain of a Washington variety. Several years (5+) of field testing are required to show that one variety is better than another. Some varieties that yield well in the early years may have a short life span. Results often are highly variable.
The variety picture in the Northeast is changing because of the results of the asparagus breeding program at Rutgers University. New hybrids that are well adapted to growing conditions in the Northeast have been developed and have been reported superior to the Washington strains. These selections include both dioecious and all-male hybrids. Dioecious asparagus plants are 50% male and 50% female. Dioecious hybrids consist of male and female plants, but male hybrids consist of all or nearly all male plants. The new hybrids, whether dioecious or all male, are reported to have greater disease resistance and to produce higher yields than the older Washington varieties or strains. Male hybrids have the additional advantage of producing no seed and, thus, no asparagus seedlings. Seedlings can become nuisance plants and as troublesome as weeds. Although cultivation destroys some seedlings, more seed is buried and later germinates and grows. Chemical control of seedlings is complicated because they are resistant to asparagus herbicides.
All the new varieties developed at Rutgers University have a high level of resistance to rust, Puccinia asparagi, although no variety is immune. A resistant variety can be attacked when the environment is highly favorable for infection and may require fungicide sprays. Rust is not a problem every year, but susceptible varieties will eventually become unproductive because of this disease.
None of the commercially available varieties are completely resistant to Fusarium oxysporum f. sp. asparagi and Fusarium moniliforme, root and crown rotting fungi, which eventually invade every planting. Some varieties, however, have considerable tolerance to Fusarium. Plant breeders are striving to develop varieties with more resistance to these soilborne diseases. To date the best methods of combating Fusarium are with the use of tolerant varieties and cultural practices that maintain plant vigor. The additional vigor inherent in male hybrids should be an advantage in the control of Fusarium. Because these diseases live in the soil many years after old plantings have been plowed up, asparagus should not be planted in fields with a previous history of this crop.
The following is a list of asparagus varieties that were developed at Rutgers and have been found to be well adapted for production in the Northeast.
Jersey Giant - all-male hybrid, widely adapted, rust resistant,Fusarium tolerant.
Greenwich - all-male hybrid, rust resistant, Fusarium tolerant.
Jersey Centennial - a dioecious hybrid, rust resistant, Fusarium tolerant.
Synthetic * 1 - a mixture of dioecious hybrids, rust resistant,Fusarium tolerant.
Synthetic #2 - dioecious, not a hybrid, tolerant to rust,Fusarium tolerant.
Synthetic #3 - a mixture of male hybrids, rust resistant,Fusarium tolerant.
Martha Washington, Brooks strain - dioecious, not a hybrid, has shown excellent vigor in New York plantings. This strain was selected from surviving plants in an old commercial field in New Jersey.
New asparagus varieties have also been developed in the western states and in Europe. Although some of these varieties have performed well in preliminary trials, it has not been determined that they have the disease resistance necessary for long-term production in the Northeast where both Fusarium and rust pressure can be severe.
Asparagus can be propagated by cloning, but varieties developed from this procedure need more research before they can be recommended for commercial production. Because of the changing variety picture, growers should seek out the latest information before planting a new field.
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Precise recommendations for fertilization of asparagus are difficult to make because this perennial crop often is more subject to differences in environmental conditions and the cultural practices of different growers than to fertilizer.
A soil test before planting will determine the need for lime and the availability of phosphorus and potassium. Apply lime, if needed, to bring the soil pH to 6.8-7.0, particularly on soils with low-lime subsoils. Asparagus grows well at a soil pH between 6.0 and 7.5. The need for minor fertilizer elements is not likely to occur unless the pH is greater than 7.5. If a large amount of lime is required to bring the pH to the desired level, plow down half of it and incorporate the remainder after plowing. If possible, apply the lime a year before planting.
If soil test data show low availability of phosphorus and (or) potassium or if no soil test data are available, incorporate 1,0001,500 pounds per acre of 5-20- 20 or similar fertilizer before planting. If soil test data show medium to high availability of phosphorus and (or) potassium, apply 500-700 pounds per acre of a 10-20-20 fertilizer. If the tests show high phosphorus and low potassium or vice versa, the fertilizer ratio can be adjusted. The potassium requirement is somewhat greater than the phosphorus requirement, but both are essential for high yields.
Once the planting has been established, it needs only moderate annual applications of fertilizer. Asparagus removes very small amounts of nitrogen, phosphorus, and potassium from the soil, even with high yields. In the spring before spear emergence or after harvest a general recommendation is to apply nitrogen (N), phosphate (P2O5) and potash (K20), each at the rate of 50 pounds per acre, and lightly incorporate them into the soil. Soils high in available phosphorus and potassium may require P2O5 and K20 applications every other year, but apply nitrogen every year. If no-till is practiced, broadcast the fertilizer, particularly the nitrogen on the soil surface, preferably before rain or irrigation.
Annual applications of high quality manure at the rate of 5 to 10 tons per acre may eliminate or greatly diminish the need for any application of mineral fertilizers. Over application of the so-called hot manures (pig, chicken, sheep) may supply too much nitrogen and result in excessive top growth and plant lodging.
The number of seeds per ounce varies between 700 and 1,200, depending on variety and growing conditions. A common estimate is 900-1,000 per ounce.
Seed may be contaminated with Fusarium oxysporum f. sp. asparagi spores and should be surface sterilized before planting (see "Diseases").
Seed is slow to germinate (table 1), and seedling emergence may require many days, depending upon soil moisture and temperature. At a soil temperature of 68° F, emergence occurs in about 15 days, but at 59° F about 24 days are required. Germination can be hastened by a presoak period. California recommends an aerated water bath of 65°-70° F for 48 hours. The USDA recommends a water temperature of 85° to 90° F for 4-5 days. After the soak period, spread out to surface dry and then dust with a recommended fungicide. Do not delay planting after presoaking.
If a precision seeder is to be used, tests should be conducted to calibrate or to determine if the seeder will handle presoaked seed. Caution: More loss than gain may result from presoaking if the job is done carelessly or with unsanitary procedures.
|Table 1. Effect of soil temperature on days to emergence of plants from asparagus seed planted 1/2 inch deep|
|Soil temperature (F°)||50||59||68||77||86||95||104|
|Days to emergence||53||25||15||10||12||20||28|
|Source: J.F. Harrington and P.A. Minges, 1954, Vegetable seed germination, Calif Agr. Ext. Mimeo Leaflet|
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The three methods of establishing asparagus fields are with crowns (roots), transplants, or direct seeding.
There are advantages and disadvantages with each method, but each one can be used successfully if recommendations and directions are followed carefully.
Crowns can be grown by the grower or purchased from a commercial plant grower (fig. 2). Advantages to the grower for growing crowns follow:
Selection of a preferred variety or source of seed is possible.
The cost is less if large quantities of plants are required (table 2).
Growing practices are under the control of the grower.
Only the best, healthy, vigorous roots can be selected for planting.
Crowns can be dug (before sprouting), and special care can be taken to prevent injury or drying before transfer to the permanent field.
Some possible disadvantages of planting crowns include the following:
Asparagus seed is small, and a precision planter is required.
Weed control can be a problem.
Sandy loam or loam soils may not be available. Heavy soils increase the difficulty of separating crowns when dug.
A mechanical digger is necessary.
Considerable time and labor are required to dig, sort, and transport the crowns.
To grow crowns, select a level, fertile, well-drained, weed-free field that has no previous history of asparagus production. Soilborne asparagus pathogens persist in the soil for many years and attack the roots of new plants. Light-textured soils are best for ease of digging. Soil pH should be 6.2-6.8. After plowing, apply fertilizer in accordance with soil tests and incorporate into the soil surface. If soil tests are not available, apply 300-400 pounds per acre of a 10-20-20 or similar fertilizer. Manure at the rate of 10-15 tons per acre can be substituted for part of the chemical fertilizer if it is free of weed seeds.
With a precision planter, space single presized seeds 1-3 inches apart in the row, depending on the germination percentage. If seed is not precision planted, tangled roots will be difficult to separate when dug. Between-row spacings can vary from 24 to 36 inches, depending on cultivation and digging equipment. Potato diggers are commonly used for digging, and between-row spacing should be selected to accommodate the machine.
Plant seeds about 1 inch deep. The depth can be 1 1/2 inches in sandy soils known to be free of crusting. Asparagus seed is slow to germinate (table 1). Germination can be hastened by presoaking the seed (see "Seed"). Soil in the germination zone must not dry out. Chemical weed control is limited to the time before seedling emergence. Thereafter, weeds must be controlled by cultivation or hand weeding.
Growers who grow their own crowns generally prefer to dig them in the spring before sprouting occurs, sometime after the middle of April to early May. Crowns can be reset in the field at this time. Potato diggers are commonly used for digging, and the operation must be done carefully to avoid root injury.
Untangle the crowns and discard the very small or badly injured ones. Sort into groups of the same relative size and plant each size group together so that competition among plants will be similar.
If planting is delayed, store crowns at 40° F and 85%-90% humidity. Do not let free water accumulate on them, but it is important not to let them dry out. If refrigeration is not available, store the crowns in a cool place out of the sun. Dip crowns in a recommended fungicide solution before planting.
Field planting of crowns
Plant crowns in a furrow with the buds up and 6 inches below the soil level of the field. Cover crowns with 1 1/2-2 inches of soil at the time of setting. Some growers use transplanters, but many plantings are made by hand. Furrows are gradually filled in, without completely covering the growing spears, until the land is level or slightly ridged over the plant row by fall.
Growers contemplating establishment of a new asparagus planting must decide whether they should grow their own crowns or purchase them from a commercial plant grower.
Commercially, asparagus crowns often are dug in the fall after the tops are completely dead from killing frosts. The crowns are separated and then stored at temperatures a few degrees below freezing and at 85%-90% relative humidity. Crowns may be advertised as 1 or 2 years old. Generally this means that the crowns have been sorted into large or small sizes, but usually all are only 1 year of age. Make sure of the age before purchasing crowns. It is questionable practice to plant 2-year-old crowns, and never plant 3-year-old crowns. The older the crowns, the greater the injury when they are dug.
Establishing asparagus fields with 10- to 12-week-old transplants is a relatively new method (fig. 3).
Some possible advantages for transplants are the following:
Seed requirements are less.
The labor and equipment required for growing and harvesting roots are eliminated.
The year required to grow roots is eliminated.
There is less opportunity to carry Fusarium from one field to another.
There is less root injury because the digging operation is eliminated.
Some possible disadvantages of transplants follow:
Greenhouse space and heat are required from mid-March to late May.
Transplants may suffer from drought unless irrigation is available.
First-year growth may be less from transplants than from crowns because of the short growing season in the Northeast.
An alternative to greenhouse growing of transplants in the Northeast is to arrange for them to be greenhouse grown in the South and shipped by air or truck in mid- to late May for field plantings in New York. Cost differences may not be great between crowns and transplants. Consult commercial root or transplant growers. Discounts often are available for large quantities. For the number of plants required per acre, see table 2 under "Plant Spacing."
It is recommended that only seed of high germinability be used for growing transplants. Plant a single seed 1 /2 inch deep per cell in the plant tray. Two seeds per cell are permissible, but not recommended. Because thinning is very difficult, planting more than 2 seeds per cell is definitely not recommended because small spears will result from plant competition in the field. Maintain greenhouse temperature at 75°-85° F day and night during germination; but after seedling emergence, reduce the day temperature to 70°-75° F and the night temperature to 60°-65° F. The frequency of irrigation and fertilization is dependent on the size of the plant-growing cells and the original fertility of the soil mix. If required, irrigate every 2 or 3 weeks with a complete nutrient solution containing the minor elements. High temperatures and too much nitrogen result in large tops and poor root development. If plants begin to get too large, growth can be slowed by reducing the temperature to 50°-60° F, but do not overharden. Use plant trays with individual cells filled with artificial soil mix. There doesn't seem to be any standard recommendation for cell size. At the University of California excellent plants have been grown in cells 1.5" x 1.5" by 2" deep with 196 cells per tray.
Figure 4. The so-called W furrow for transplants or direct-seeded asparagus. Seeds or transplants in the center of the mound of soil in the bottom of the furrow are protected from drowning, washing out, or smothering from washed-in soil.
Use spacers or screens to keep trays off tables for "air pruning" of roots. If trays are placed on solid benches, the roots grow through the holes in the bottom of the cells and make seedling removal difficult. After danger of frost is past, remove transplants carefully from the trays, and plant in the field by hand or with transplanters that have been modified to run in the bottom of 5-to 6-inch-deep furrows. New Jersey recommends that a special-type furrow (fig. 4) be used for transplants. The transplants are set in a raised mound in the bottom of the furrow. The mound provides the transplants with some protection from washing out or being covered up with soil washed into the furrows by heavy rains. Set the transplants slightly deeper than they were in the plant cell. As the plants grow, gradually close the furrows with cultivators or hoes until the soil surface is level or slightly ridged over the plant row by mid- or late August. Filling the furrows provides some . weed control in the rows. There are no persistent herbicides for newly established asparagus plantings.
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|Figure 1. Deformed spears that emerged after injury from a below ground freeze. Spears aboveground were completely killed.||Figure 2. One-year-old asparagus crowns. The larger and better crown is on the left.||Figure 3. Eleven-week-old seedlings ready to set in the field.|
A few growers direct-seed asparagus. This method requires considerable expertise. The seed bed in the bottoms of the furrows must be more thoroughly prepared than for crowns or transplants. Irrigation may be needed for seed germination and plant emergence if dry weather persists. Weeds may become a problem before the slow-growing asparagus can be adequately cultivated. There are no labeled persistent herbicides for direct-seeded asparagus.
Furrows 5 to 6 inches deep are opened the same as for transplants. New Jersey recommends the same W-shape furrow used for transplants. Precision planters are used to space single seeds 2 1/2 3 inches apart and 1 1 1/2 inches deep. in the bottom of the furrows. It is essential that seeds be in firm contact with moist soil and that the soil does not dry out during germination. Thinning of plants is not a standard practice, but if done, it must be accomplished shortly after seedling emergence. Once plant growth has developed enough to permit cultivation without covering the young plants, the furrows are gradually closed with cultivators or hoes until the soil surface is level by fall.
When ready to plant, open furrows with potato hilling shovels (middle busters, double mold-board plows, etc.) Recommendations call for the bottom of the furrow to be not less than 5 inches or more than 8 inches below the level soil surface for roots, transplants, or direct seeding. Do not plant into subsoil. Growers with lighter soils tend to plant at the greater depth. Deeper plantings lessen the danger of injuring roots or crowns during future tillage operations. In the spring, spears emerge earlier from shallower plantings. Deeper planting and later emergence may be preferred where late frosts frequently occur. Spear size tends to be larger from deep, compared with shallow, planted crowns.
Spacings between and within rows are the same for both crowns and transplants. Recommendations for between-row distances of commercial plantings vary somewhat among experiment stations, but, in general, are 4 1/2 6 feet (table 2). Choose a spacing within this range that will accommodate cultivators, tractors, fertilizer spreaders, and the like that are used routinely in the other farming operations. In a healthy, vigorous-growing asparagus field the crowns will spread in all directions, "to the size of a bushel basket." Rows spaced too close will eventually have little or no space between them for machinery or harvesters.
Recommendations for within-row spacings also vary, but generally are from 10 to 18 inches. In the earlier years of harvest, yields are likely to be higher from the closer-spaced plants, whether within or between rows. Eventually these differences will decrease. Spears may be smaller from crowded plants during the early life of the asparagus field.
Table 2. Number of plants per acre
Between rows (feet)
Between plants (in.)
Although it is not a common practice to irrigate asparagus in the Northeast, the productivity and longevity of the bed will increase if plantings are irrigated. In addition, irrigation may improve the overall vigor of the planting and thus decrease the risk of infection with Fusarium. Because new varieties, especially the male hybrids, are inherently more vigorous than the older standard varieties, special care should be taken to provide them with adequate water, especially during the first 2 years in order to maximize their growth and yield potential.
Irrigation practices for asparagus should change with the age of the planting. The perennial root system of asparagus becomes quite extensive and, after a few years, can penetrate the soil to a depth of 4 feet or more. Consequently, there is usually less demand for supplemental irrigation in older asparagus plantings with well-developed root systems than in newly established beds.
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Whether seedling transplants or crowns are used to establish the bed, irrigation practices in first-year beds should approximate those used for annual vegetable crops with relatively shallow root systems. One inch of water per week whether from rain or irrigation from mid June to the end of August should result in good growth of the fern and provide sufficient carbohydrate for both crown development and spear growth the following spring. If tensiometers are used to schedule irrigation, they should be placed at a depth of 6 inches, measured from the bottom of the planting furrow. New beds will benefit from irrigation when the tensiometer gauge indicates a reading of 50. In the year after planting, spears may start to emerge anytime after about mid-April. There is usually adequate spring rainfall for early fern growth, and supplemental irrigation may not have to be applied in the second year until after mid June.
The water requirements and irrigation practices of an established asparagus planting can be divided into three periods:
April-May. The water requirement is low because harvest of the spears prevents water loss that would otherwise occur through development of the fern. Rainfall usually provides enough water at this time of year to prevent the need for supplemental irrigation.
June. The water requirement rapidly increases after the spears are allowed to develop into ferns. The increase in water requirement is often accompanied by a decrease in rainfall. In a mature bed, roots may be rather extensive and deep, making irrigation unnecessary until the end of June. However, it has been observed that following a cutting season that has been rather dry, spear emergence and subsequent fern development may be delayed. This delayed emergence following harvest may be prevented by beginning irrigation immediately after the last cutting, particularly in a dry year.
JulyAugust. In an established planting, the most critical time for irrigation is generally July and August when ferns become large. A good water supply at this time allows for maximum fern growth and, consequently, maximum transport of carbohydrates to storage roots. The amount of water applied should be sufficient to wet the soil to a depth of about 2 feet.
Irrigation may be detrimental after the end of August. Although asparagus is fairly cold hardy and can continue to grow well into the fall, excessive fern growth late in the season may deplete the root system of carbohydrates, which would be better used in the next spring's spear production. Withholding irrigation in the fall helps asparagus go into the dormant period necessary for successful production in the Northeast.
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The importance of choosing a field as weed free as possible for the initial planting is noted under "Field Selection."
In the first year, or the year the asparagus is planted, use a row crop cultivator to control weeds and fill in the open furrows. Small plantings can be kept weed free with hoes. Very few herbicides are labeled for use the first year and may be of limited value.
Weed control the second year begins the same as for the third year (see next paragraph); but because this is a no-harvest year, there is no opportunity for tillage after harvest. Several herbicides are labeled for use beginning with the second year.
In general, weed control in established asparagus fields begins by disking or rototilling the entire field in early spring before emergence of any spears. This operation should be done as soon as the soil is sufficiently dry to permit use of machinery. There will be some loss of yield if underground, but not yet emerged, spears are destroyed. Do not drive tractor tires on the plant row, and use equipment with precision depth control to avoid damage to crowns or roots. Some growers do not cultivate during the harvest season, but others cultivate and mound soil over the plant row as the harvest season progresses. This operation helps to destroy small weeds and asparagus seedlings. The mound of soil over the row is also believed to increase spear size and decrease soil temperature at the crown. Shallow disking or rototilling is done immediately after the last harvest to level off the mounds or ridges. A delay in the postharvest tillage will delay regrowth of new spears and ferns and further weaken the crowns and roots.
Either the tillage operation before spear emergence in the spring or the one after harvest can be used to prepare the field for application of a herbicide or to incorporate an already applied herbicide, fertilizer, manure, lime, or plant debris.
Cultivation during the fern stage the second year and thereafter is not feasible or is very difficult because asparagus plants grow rapidly to a height of 5 feet or more. If cultivation is attempted after harvest, keep the shovels well away from the base of the plants to avoid cutting off new spears, which can be either above or below ground.
Because of frequent changes in company labels and recommendations, no herbicides are named in this publication. Only a general discussion is given here. For information on asparagus herbicides, consult a local Cooperative Extension agent.
The large number of herbicides labeled for asparagus may cause confusion as to which one or ones to use. First, determine the weed problem, that is, are the weeds emerged or not emerged, annuals or perennials, grasses or broadleaves. Then select and use the herbicides that best fit the problem. Some herbicides control only germinating or sprouting weed seeds and provide little, if any, control of weeds already emerged. Some herbicides are effective only when applied postemergence, that is, applied to the leaves of growing weeds. Some herbicides are systemic in action, that is, after contact with leaves they are translocated throughout the plant including the underground parts. Systemic herbicides can cause severe damage if they contact the asparagus plants. One or more asparagus herbicides in each of these groups are available.
From the foregoing discussion it is obvious that the two most opportune times for application of asparagus herbicides are before first emergence of spears in the spring and again after harvest when all spears have been cut down. Some herbicides can be applied with shielded or directed sprays to prevent contact with spears or foliage.
No-till asparagus is possible with herbicides. No-till, at least for 2-3 years, is practiced by some commercial growers. Fields generally are disked or rototilled after a time to level ridges or to incorporate plant debris, fertilizer, manure, or lime.
Asparagus seedlings, unless controlled, can become as much of a problem as weeds. These seedlings grow from the seed produced by the female plants in dioecious plantings. Even if the majority are killed by cultivation or tillage, the remaining few seedlings compete with the established plants and result in small spears and reduced yields. Cultivation also buries more seed, and a new flush of seedlings may appear. Once firmly established, seedlings are difficult to kill with cultivators, very difficult to chop out with hoes, and impossible to pull up. If control is by cultivation alone, it must be done early in the life of the seedlings.
Seedlings are resistant to most of the asparagus herbicides, but are susceptible or partially susceptible to some of them. Herbicide rate per acre and time of application in relation to the growth stage of the seedlings are critical. Consult a local Cooperative Extension agent for information on seedling control with herbicides.
Seedlings are not a problem in all-male hybrid fields; but if a few female plants appear, destroy them as soon as they are identified by the presence of seed balls.
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The main diseases of asparagus are Fusarium stem and crown rot caused by Fusarium moniliforme, and (or) F. oxysporum f. sp. asparagi, Fusarium wilt and root rot caused by F. oxysporum f. sp. asparagi, and rust caused by Puccinia asparagi. One or both Fusarium spp. may be present as soilborne pathogens wherever asparagus is grown in the United States. Other names applied to this disease complex are seedling blight, decline, or replant problems. To illustrate the importance of Fusarium, asparagus decline is the principal factor responsible for the reduction of asparagus acreage in New Jersey from 32,500 acres in 1957 to 2,300 acres in 1977. Both pathogens can enter the plant through young feeder roots, spread throughout the root and crown regions, and eventually weaken and kill the plant. F. oxysporum f. sp. asparagi causes reddish brown vascular discoloration and decay of feeder and storage roots (fig. 5) and occasionally discoloration and rot of crowns and stems. By contrast, F. moniliforme is associated primarily with stem and crown lesions (fig. 6) and rarely with root tissue. In New Jersey, F. moniliforme is infrequently recovered from 2-year-old plantings, but is the dominant species in 12-year-old plantings. As both fungi increase in the soil over a period of years, yields progressively decline, and the disease can be intensified by nutrient stress, drought, and insect damage. Winter injury may be confused with Fusarium root and crown rot (fig. 7). Fusarium can be introduced into the field from diseased crowns or infected transplants. Select only disease-free material, and dip the roots in a recommended fungicide solution. Seed may be surface contaminated with Fusarium spores. Disinfect the seed for 2 minutes in a solution of 1 part commercial 5.25% sodium hypochlorite to 4 parts water. Remove the seed from the solution, rinse thoroughly with cold water, and spread out to surface dry, and then plant immediately unless presoaking is planned. Select well-drained fields where asparagus has never been grown. If this is not possible, select fields that have been out of asparagus for at least 8 years.
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|Figure 5.Fusarium wilt Fusarium oxysporum f.sp. asparagi. Note reddish brown lesions on top root and vascular discoloration in cut bottom root. Photo by S.A. Johnston, Rutgers||Figure 6. Crown rot (Fusarium moniliforme and/or F. oxysporum f.sp. asparagi). Photo by S.A. Johnston, Rutgers||Figure 7. Winter injury. Note brown discoloration and shriveled roots on left. Photo by S.A. Johnston, Rutgers|
Asparagus rust can be a potentially devastating disease if left untreated. Symptoms of the disease first appear as small orange patches on spears (fig. 8) and on fern branches. High humidity and warm temperatures influence repeated spore production and germination. Windblown spores are spread to adjoining plants, and with sufficient moisture new infections are initiated. Individual fern needles are shed, and the entire field may turn brown. The entire life cycle of the rust fungus occurs on asparagus, with the summer orange spores giving way to black overwintering spores (fig. 9). Plant resistant varieties if possible. Some varieties selected out of Washington strains have some rust resistance. Several New Jersey selections have good to excellent resistance. Several fungicides are labeled for the control of rust. See labels for specific amounts; begin application when first signs of the disease appear (early August) and repeat at 7-10-day intervals as required to maintain control. Destroy wild asparagus plants and volunteer seedlings in the vicinity of the crop. Removal and burning of the infected asparagus ferns in the fall do not appear to be an effective control measure.
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|Figure 8. Rust (Puccinia asparagi). Early stage showing orange uredospores in pustules. Photo by S A. Johnston, Rutgers||Figure 9. Rust (Puccinia asparagi).Overwintering black teliospores on branches dead fern. Seedballs are present.Photo by S A. Johnston, Rutgers||Figure 10. Adult of the common asparagus beetle (Crioceris asparagi) on left and adult of the 12-spotted asparagus beetle (Crioceris duodecimpuncata) on right.|
Three insects may be quite troublesome to asparagus grown in the Northeast. The most-common pest is the asparagus beetle, Crioceris asparagi (fig. 10). The adult beetles, which overwinter under plant refuse and debris along field borders, begin to move to asparagus as the spears first emerge in the spring. The beetles feed on the spears and lay eggs singly in vertical rows, usually near the tip of the spear (fig. 11). The eggs hatch in approximately 1 week, and the numerous fleshy, grey larvae move to foliage where they feed. The larval stage lasts 2-3 weeks, after which the larvae leave the plant, burrow into the soil, and pupate. Two or three generations are produced during the growing season in New York.
Another beetle with similar habits and life cycle may also be a pest. This is the 12-spotted asparagus beetle, Crioceris duodecimpunctata (fig. 10).
The beetles; eggs, and larvae of these two asparagus beetle species are present from the first spear harvest until fall because of overlapping of generations. Extensive spear damage may result from beetle feeding, which causes a distorted spear growth with a distinct "shepherd's crook" shape. Spears with eggs attached are also unacceptable for market.
Production practices that promote plant vigor and thorough harvesting of all spears during harvest season may help reduce the beetle populations. The fern growth and spears of new plantings not yet in production may be severely damaged by uncontrolled beetle populations.
The third insect pest that is potentially very destructive is the asparagus aphid, Brachycolus asparagus. This fairly small, blue green aphid feeds on the fern. The feeding results in a "witches'broom" growth of the plants (fig. 12). The damage results in short, bushy plants with a distinctive silvery, blue green color. Crowns may be affected, resulting in thin spears and poor yields. Do not allow this aphid to become established, for its damage will greatly reduce the stand for following years.
In addition to the three foregoing insects, other aphids and leafhoppers can be a problem, especially on young plantings. Asparagus miners can damage spears at the base of the plants and allow Fusarium to enter the plant more readily. Where the Japanese beetle is a pest, it can severely strip the foliage from asparagus plants. Asparagus spears are killed or seriously injured by the tarnished plant bug. Most damage occurs to young spears in the field after harvest. The toxin injected by this insect causes the spears to turn brown and cease growth. Control of the tarnished plant bug is very difficult and may be impractical. Whether it causes a significant loss of yield is not known.
Bee poisoning: Bees collect pollen from flowering asparagus. Key points to remember when using toxic pesticides: (1) read and follow the warning about bees on the label; (2) do not spray when the plants are in bloom; (3) spray early in the morning or late in the evening to avoid bee contact.
Several chemicals have been registered for control of asparagus insect pests. Consult your local Cooperative Extension office for specific control recommendations.
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The treatment of the plants in an asparagus planting following the harvest season is very important and will influence the productivity and ultimate longevity of the bed. The shoots that are allowed to go to fern over the summer months carry out photosynthesis and produce carbohydrates. Thus, the larger the fern and the longer it is maintained in a healthy vigorous condition, the greater is the production of reserve carbohydrate or energy for the next harvest season. Competition from weeds, insects, or disease during the growing season will reduce fern growth and yield potential for the following spring. Not only does such competition reduce the production of reserve material available for spear production, but it can also make asparagus more susceptible to Fusarium. Plantings should be monitored for evidence of rust or insect infestations and sprayed throughout the season as necessary.
Irrigation can also improve the vigor of an asparagus planting. Although it is a deep-rooted crop, asparagus is responsive to irrigation and should be irrigated routinely throughout the summer to maintain fern vigor until early fall. Because it is a perennial and can be maintained in essentially a no-till situation, asparagus may be a good candidate for a trickle irrigation system, especially in the early years of establishment before roots have had time to penetrate soil to a large extent.
As long as ferns retain any green color, they are still transporting valuable nutrients to the roots. Consequently, delaying the cutting back of the fern until late winter or early spring allows maximum transport of reserve to the storage roots. An additional advantage to allowing the fern to stand through the winter is that it can provide some protection against soil erosion and catch a snow cover, which can provide protection against crown or root damage from freezing injury (fig. 13). Fern residue can be incorporated into the soil in the spring, but any sort of tillage in asparagus should be quite shallow so as not to damage root systems. Damage to asparagus roots by tillage can reduce yields as well as increase the possibility of infection with Fusarium.
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|Figure 11. Egg rows of the common asparagus beetle (Crioceris asparagi).||Figure 12. Witches'-broom caused by the asparagus aphid (Brachycolus asparagi)||Figure 13. A snow cover caught by standing asparagus brush povides protection against freeze damage to crowns.|
First harvest begins the third year after field planting (plant 1985, first harvest 1987). As a rule of thumb, harvest for 2 weeks the first year, 4 weeks the second year, and 6 weeks the third and following years. These are only general recommendations, and harvest may continue as long as spear size and regrowth are maintained. Once there is a noteable increase in numbers of small-diameter spears (table 3), harvest should stop. It is a common mistake for new growers to harvest too long. Overharvesting can cause a permanent reduction in vigor and health of the plants and reduce yields the following years.
Table 3. USDA classification of asparagus spear diameter measured approximately 1 inch from the butt end
The growth of asparagus is erratic because spears grow very rapidly on warm days and very slowly on cool days. In warm weather productive plantings must be harvested at least once each day. Rather than harvest twice a day, some growers harvest only once, but take all spears that are 4-5 inches or more in height. In warm weather buds begin to open at a shorter spear length than in cool weather. Closed tips are associated with high edible quality.
Injuries to growing spears, even if only slight, cause them to bend toward the side where the injury occurred. Injuries result from several causes. Spears grow bent in one direction toward a strong wind. If all the spears bend sharply in one direction, the wind drove sand or dirt particles into them. Other causes of crooked spears are crusted soils, stones, insects, cutting knives, and harvesters' footsteps.
USDA Grade Standards do not specify a standard spear length, but a common trimmed length is 9 inches. U.S. #1 asparagus is clean, firm, tender, well trimmed, fairly straight, and nearly free of mechanical, insect, and disease damage. Spears are at least 2/3 green and, unless otherwise specified, are 1/2 inch or large in diameter about 1 inch from the butt end. The terms provided by the USDA to describe diameter classification are given in table 3.
In some markets the demand for fresh and attractively packaged very small or small spears may be good, although the edible quality is inferior to that of larger spears because of higher fiber content in small spears. Growers planning to ship or market asparagus through wholesale channels should obtain a free copy of the United States Standard Grades for Fresh Asparagus from Fresh Products Standardization and Inspection Branch, Fruit and Vegetable Division, Agricultural Marketing Division, Agricultural Marketing Service, U.S. Department of Agriculture, Washington, DC 20250. These standards show the tolerance allowed for variability within the No. 1 and No. 2 grades. A separate set of standards is available for processing asparagus.
In the field, spears are harvested when 8-10 inches tall and placed in crates, baskets, or buckets. If harvesters are provided with containers near this height, they occasionally can check to see if they are taking spears that are too short or too long. Lightweight plastic buckets are ideal because they are easily kept clean. Some harvesters prefer picking aprons, which are similar to a carpenter's apron, but have only one large pocket.
Asparagus is harvested by cutting or snapping by hand. A common cutting instrument is the V-shaped hand weeder often used to dig dandelions from lawns. Pointed, short-handled knives are also used. Spears are cut 1 inch or more below the soil. Experienced harvesters can cut asparagus rapidly in stone-free soils. This method results in a large percentage of white color at the lower end of the spears. The white area is fibrous and tough and of poor edible quality. Cutting below the soil may also result in injury to underground spears that are about to emerge. Most asparagus shipped to wholesale markets is cut below ground.
Most of the asparagus grown for U-pick, roadside stands, or other local fresh market outlets is snapped at or near the ground level. If the spears have grown too tall, they are grasped below the tops and pushed forward until they snap off. All or nearly all the portions above the break will be green and edible. With snapping there is no cutting injury to spears still underground.
The best method of harvesting U-pick asparagus is by snapping. Customers like this method because it is rapid and easy and there is little, if any, trimming loss when the spears are prepared for the table.
U-pick growers devise various schemes for scheduling customers for harvest. Advertisements may state that harvesting will be only between certain hours. If the acreage is small with a limited quantity available each day, customers can be scheduled by telephone reservation. Advertisements should state the hours telephone calls will be accepted for reservations. All scheduled customers can be asked to arrive at or between certain hours. Growers should be prepared to harvest some of the crop on days when there is a lack of U-pick customers. This asparagus can be used to fill orders from customers who do not want to U-pick or can be sold to other local outlets.
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Quality quickly declines in asparagus if not cooled immediately after harvest. Both sugars and vitamin C decrease rapidly, resulting in a loss of flavor and nutritional value. In addition, if the storage temperature is above 36° F, fibers develop in the spears, resulting in a tough, stringy texture, and the tip buds begin to open.
Harvested spears that are to be sold to consumers within a few hours should be stored in a cool place away from sunlight to prevent wilting. Spears that must be held for 24 hours or longer or are to be shipped to wholesale markets should be washed and chilled with cold water. If hydrocooling is available, a water temperature of 32° F for 5 minutes will lower the spear temperature to about 40° F. Once asparagus is chilled, it can be stored up to 3 weeks at a temperature of 36° F and 95% relative humidity. High relative humidity can be obtained by packaging spears in perforated film. Nonperforated film is not recommended because of injury from increased carbon dioxide and decreased oxygen within the package. An increase of ethylene in nonperforated film also has been reported to cause toughening of spears. Storage at 32° F for 10 days will result in chilling injury. High temperatures, in addition to causing a more-rapid decline in quality, may result in mold development. If it is to be shipped, asparagus is usually packed either loose or in bunches in pyramid crates with a capacity of either 15 or 30 pounds. A traditional method of storing asparagus has been to place the butt end of the spears in a shallow pan of water or on a dampened waterabsorbent material. Unless the asparagus is refrigerated at low temperatures, this method will result in elongation of the spears and opening and growth of tip buds and side scales, with a decrease in general appearance and quality. Most New Yorkgrown asparagus is marketed direct through roadside markets, farmers markets, or U-pick operations, although there is some direct wholesale by growers to local retail markets. Whatever the market outlet, it is important to maintain postharvest spear quality in a low-temperature and high-humidity environment. Asparagus sold at farmers markets and roadside stands is often tied in 1-2pound bundles for transport. Although asparagus does not have a long shelf life, it can be displayed for up to 10 days under the conditions described as appropriate for shipping.
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