AGRICULTURE, FOOD AND NATURAL RESOURCES

Asparagus production guide Vincent A. Fritz, Carl J. Rosen, William D. Hutchison, Roger L. Becker, Janna Beckerman, Jerry A. Wright, Cindy B.S. Tong, and Terry Nennich Washington, and Michigan, many other areas TABLE OF CONTENTS have great production potential climatically and geographically. The cost to establish an  Climate field is substantial, so the decision  Site selection and preparation to grow asparagus is one that should be  Soil fertility requirements – new thoroughly investigated. This publication plantings describes the cultural practices that must be  Soil fertility requirements – considered to produce asparagus established plantings successfully.  Secondary and micronutrients  Irrigation  Asparagus varieties  Asparagus bed establishment  Crown plantations  Seedling transplants

 Pest management o Insects Crown and root system of a six-year-old asparagus plant; Weeds o each block represents one foot square. o Diseases  Harvesting CLIMATE o Preparing for harvest Production is most successful in areas where o Harvest freezing temperatures or drought terminates plant growth and provides a rest period. o Field maintenance after harvest Without this rest period, reduced yields are

likely. Asparagus tolerates great temperature Asparagus is a high value specialty crop and variations: it grows in the Imperial Valley of the earliest producing spring vegetable. It Southern California, where temperatures can currently is priced as a gourmet item and will reach 115° F, and it grows in Minnesota, remain in this category until growing, where temperatures can plunge to -40° F. harvesting, and processing costs can be Asparagus can be grown in a wide range of reduced. Although production in the United soils and under various climatic conditions, States is concentrated in California, but it thrives in fertile well-drained soils in

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moist temperate regions that have long and 3 for suggested rates of fertilizer. For growing seasons and sufficient light for nitrogen, (N) approximately 1/3 to 1/2 of the maximum photosynthesis. recommended rate should be broadcast after planting. The remainder of the N should be In Minnesota, asparagus is susceptible to late sidedressed at the first cultivation. Most of spring frosts that may kill emerged spears, the phosphorus (P) and all of the potassium delaying subsequent spear development. (K) should be broadcast and incorporated Therefore, production fields should not be prior to furrow construction or bed shaping. established in low areas or in other frost- Apply 25-30 lb/A P205 in the trench before susceptible locations. crown setting. If soil test P is high, omit the broadcast application and apply only that SITE SELECTION AND PREPARATION recommended for the trench. Unlike most other vegetables, asparagus is a perennial crop which can be productive for Table 1: Nitrogen recommendations for asparagus 15 years or more. Consequently, it is Asparagus Organic matter level How to apply important to pay particular attention to site selection and preparation for this crop. In Low Med. High

Minnesota, asparagus is grown on many N to apply lb/A different soils ranging from sandy coarse- New planting 120 100 80 ½ broadcast, ½ sidedress textured soils to clay fine-textured soils. during cultivation Highest yields are usually obtained on Established 80 60 40 Topdress after harvest medium-textured sandy loam to loam soils. planting Asparagus plants have a deep root system that will penetrate at least six feet. Shallow soils or soils prone to a high water table should be avoided. Asparagus roots will not Table 2: Phosphorous recommendations for asparagus tolerate saturated soil conditions.

Phosphorous (P) soil Amount of Phosphate (P2O5) to apply SOIL FERTILITY REQUIREMENTS - NEW test (lb/A) PLANTINGS ppm New Established Field preparation should take place the year 0-10 200 75 prior to planting. Soil tests (0-12") can be 11-20 150 50 used to determine needs for lime, 21-30 100 25 phosphorus, and potassium. Asparagus will 31-40 50 0 not tolerate extreme acid soil conditions and 41+ 25 0 grows best at a pH of 6.5-7.0. The objective during the first 3 years after planting is to encourage maximum fern growth so that plants build extensive storage root systems. Plow down soil amendments before furrow construction or bed shaping. All furrows should be 6 to 8 inches below the normal soil surface. Rates of fertilizer for asparagus are dependent on soil test values and relative organic matter levels. Refer to Tables 1, 2

development. Tables 1, 2 and 3 present Table 3: Potassium recommendations for asparagus fertilizer recommendations for established

Potassium (K) soil test Amount of Potash (K2O) to apply (lb/A) plantings. This fertilizer should be lb/A New Established topdressed after harvest to encourage fern growth. 0-50 250 100 51-75 200 75 SECONDARY AND MICRONUTRIENTS 75-100 150 50 Asparagus response to application of 101-150 100 25 secondary and micronutrients is not well 151-200 50 0 documented in Minnesota. Most soils low in 200+ 0 0 calcium (Ca) and magnesium (Mg) are acid and should be limed with dolomitic lime prior to planting. Sulfur may be limiting on For the second and third year following sandy soils with low organic matter. In crown setting, disk in during the spring prior general, asparagus response to to spear development (40-60 lbs. N/A and micronutrients is low. Nutrient ranges from recommended rate of P and K according to a healthy mature asparagus ferns are soil test). An additional 30-40 lbs. N/A presented in Table 4. Suspected nutrient should be applied as the soil warms up. deficiencies should be confirmed with soil tests and/or tissue analysis. SOIL FERTILITY REQUIREMENTS – ESTABLISHED PLANTINGS IRRIGATION Once the plants are established, the primary Irrigation should be used on asparagus fields objective is to maintain plant vigor. containing sandy soils or shallow root Asparagus has a very fleshy root system restrictions in central Minnesota. Inadequate which is capable of storing a large quantity of soil moisture during fern development can nutrients. It has been estimated that the cause significant reduction in next spring's roots can store 150 lbs. N/A, 37 lbs. P/A and spear production. Dry soil conditions during 170 lbs. K/A These stored nutrients, in part, spear growth can also affect quality and can be used for the development of spears in yield. the early spring. The actual amount of nutrients removed by a 2.5 T/A harvest is 23 Adequate soil moisture is also necessary for lbs. N/A, 3 lbs. P/A and 20 lbs. K/A. newly planted crowns to establish good root Generally, it is not necessary to apply development and fern growth. fertilizer for an asparagus crop until after Asparagus roots can penetrate up to 10 feet harvest. Delaying fertilization until after to obtain soil water if not restricted but their harvest can reduce early weed growth. For greatest water uptake occurs from the top 6 sandy coarse-textured soils, 20-25 lbs. N/A in to 24 inches of rooting zone (See cover). the spring may be beneficial for spear Maintaining adequate soil moisture in this

Table 4: Nutrient concentration ranges in healthy asparagus ferns

Stage of Growth Part sampled N P K Ca Mg Fe B Cu Zn Mn

------% ------ppm ------

Mature fern Fern from 18”-36” up 2.4 0.3 1.5 0.4 0.15 --- 50 6 20 20 3.8 0.4 2.4 0.5 0.20 --- 100 11 60 160

zone during the fern stage especially should dioecious (dye-EE-shus) plant, meaning that be the goal of an irrigating producer. there are both male and female plants. Asparagus plants will use .10 to .20 inches of Generally, females produce larger spears soil water per day during fern growth than males, but the males produce greater depending on climatic conditions. numbers of smaller diameter spears. Only female plants produce berries. Breeding work To maintain healthy fern development, soil is in progress worldwide to produce high moisture during this period should not be yielding all male asparagus lines. The main allowed to deplete more than 50 to 60% of benefit from an all-male hybrid is that it the soil's water holding capacity in the active doesn't produce seed, which can later rooting zone or go beyond a soil tension of germinate and create a significant weed 70 centibars before another irrigation. problem in the form of several volunteer Asparagus plants do not generally show asparagus seedlings. Asparagus spears visual signs of wilting when moisture- produced from all male hybrids are usually stressed, so extra care must be exercised to very uniform. For many years, the most ensure there is adequate soil moisture common varieties have been from the throughout the growing season. Washington series (Mary, Martha, Waltham), Several soil moisture monitoring methods are developed by the U.S. Department of available to assist the grower in proper Agriculture which are dioecious. However, timing of irrigation water to maintain healthy several of the all-male hybrids developed in plant growth. A discussion of the typical New Jersey (Rutgers University) offer proven monitoring methods can be found in higher yields and increased resistance University of Minnesota Extension article, and tolerance to fusarium crown rot and are Irrigation Water Management Considerations often the preferred choice. 'Jersey Giant', for Sandy Soils in Minnesota. 'Jersey Knight', and 'Jersey Prince' have done well in Minnesota. Other all-male hybrid Light, frequent irrigation applications should varieties released from the Jersey series with be avoided during fern growth to minimize excellent resistance to fusarium include foliage disease development. On the other 'Jersey Jewel', 'Jersey King' (green spears with hand, over irrigation should also be avoided purple bracts), 'Jersey General', and 'Jersey as it may cause some of the applied nitrogen Titan' (green spears with purple bracts). to be leached below the plant's root zone and These have not been tested in Minnesota but possibly into the ground water. have been reported to do well in other states, Water scheduling is an essential management including Michigan, and Canada. A newer all practice for irrigated asparagus production. male hybrid released from the University of Utilization of any of the available soil Guelph called 'Guelph Millenium' has moisture monitoring tools requires only performed very well in Canada but has not about 30 minutes a couple times a week to been evaluated in Minnesota. An open- provide an operator with valuable pollinated variety that has been grown for information for scheduling the next years in Minnesota is Viking KB-3. Although irrigation. this variety is a proven survivor in Minnesota conditions, many of the Jersey hybrids will ASPARAGUS VARIETIES offer better results. However, it should be noted that in northern Minnesota the Jersey Asparagus varieties should be both high hybrids have had winter kill at temperatures yielding and disease resistant. Asparagus is a of -30°F with no snow cover. Purple Passion is

a variety that produces attractive purple Usually one ounce of asparagus seed spears for an added twist. This unique contains 500 to 700 seeds. variety could provide a niche market To grow high quality crowns, obtain seed opportunity. Varieties from California have with a high percentage. Plant the been bred for warm climates and do not seed in sandy soils so crowns can be easily possess the longevity or hardiness needed in dug and will be relatively free of soil. Apply Minnesota. One of the key attributes and incorporate phosphorus and potassium associated with California varieties has been fertilizers prior to seeding the nursery at the their strong production potential during very rates suggested in Table 2. Apply warm conditions and delaying the onset of approximately 50 pounds per acre of fern development. However in Minnesota, nitrogen after the first shoot ferns out, and yield decline has often been observed in topdress an additional 50 pounds per acre in these varieties shortly after the midsummer. establishment years. The slow rate of germination is a problem ASPARAGUS BED ESTABLISHMENT with direct seeding. Optimum temperatures for germination range from 77 to 86° F. Commercial asparagus plantations can be Although lower soil temperatures slow established either by traditional crown germination, it is advisable to plant planting or by transplanting seedlings. Direct asparagus seed as soon as the soil is seeding into a permanent location is workable in the spring. Since the growing discouraged because of the difficulty of season needed to produce large crowns is establishing a stand. If you are planting a limited in Minnesota, early spring seeding large acreage, asparagus crown nurseries will allow germination to occur as soon as offer the opportunity to produce many the soil environment becomes favorable. To crowns per acre easily. Generally, ten prevent infection by soilborne pathogens, production acres can be established from the asparagus seed should always be treated with crowns produced in a one-acre nursery. One fungicides. pound of asparagus seed will produce enough crowns to plant one acre. Asparagus Weed control in direct-seeded asparagus seed with a high germination percentage presents a second challenge. A few should be seeded on level ground about one satisfactory preemergence herbicides are inch deep and spaced about two inches apart labeled for direct-seeded asparagus. Adjust within rows. Row width should accommodate the rate according to the texture of the soil machinery to facilitate mechanical digging. A type. Inevitably, mechanical cultivation is modified potato digger has been used necessary in the nursery. Any cultivation successfully to dig crowns. Generally, single should always be shallow to prevent damage rows spaced about 24 inches apart will allow to asparagus roots, which are very near the enough space for large crown production. soil surface. Although mature asparagus is This spacing scheme requires 130,000 seeds quite drought-tolerant, seed beds are shallow per acre for the planting. An 80-percent rooted and require constant water recovery of crowns will net approximately management Irrigation should be available enough plant material to plant ten on demand. production acres with four feet between rows Asparagus crowns should be dug in early and one foot between plants within rows. April or before the buds have begun to grow. Old plant tops should be mowed and

removed from the field if they interfere with of larger diameter and emergence is delayed. crown digging. A potato digger, peanut In addition, as crowns grow in mass, they digger, or common moldboard plow can be 'migrate' upward making the crown more used to lift the asparagus crowns from the susceptible to frost damage during first nursery row. Avoid injury to the crowns spear emergence. Planting crowns closer than during digging and handling. If dug crowns 12 inches results in reduced spear size and need to be stored prior to replanting, keep quality. Spacing crowns farther than 18 them cool (about 38° F) and dry. High inches apart may result in larger spears but humidity will cause rapid decay. Crowns can fewer spears per acre. become overheated if they are stored in a deep pile. Crowns in storage should be stacked only a foot or so deep. Avoid freezing temperatures in storage, since severe injury or even complete loss is probable. Figure 2. Side view of typical furrow construction. X = crown or transplant placement; F = fertilizer placement (two-three inches below the bottom of the furrow). CROWN PLANTATIONS For small plantings, it is easiest to buy one- After placement in the furrows, cover the year-old crowns from a reliable grower. Only crowns with two to three inches of soil (see one-year old crowns are recommended which Figure 3). Gradually fill in the furrow as transplant easier, produce as vigorous plants shoots emerge. By the end of the season, the as two-year-old crowns, and are less furrows should be entirely filled in, although expensive Crowns should be large, with many the developing asparagus fern should never storage roots and buds (see Figure 1). Each be buried. bud will eventually produce a spear. Storage roots contain high levels of sugar that nurture the developing spears. The larger the crown, the more vigorous the resulting asparagus plant will be.

Figure 3. Planting crowns: (1) set crowns upright in wide furrows, six to eight inches deep, with roots spread. (2) cover with two inches of soil, (3 and 4) gradually fill the furrow as the plants grow.

Figure 1. A high-quality asparagus crown Weeds cause the greatest problem in establishing an asparagus bed from crowns. Crowns usually are hand planted with buds All perennial weeds should be eliminated up, spaced 12 inches apart within rows in before planting any asparagus. An furrows four to five feet apart (9000 to appropriate herbicide, applied immediately 11,000 crowns per acre). Six to eight inches is after the crowns are covered should control the optimum depth for crown planting (see weeds until the asparagus is large enough to Figure 2). Shallower planting depths cause be cultivated easily and safely. production of spindly, thin spears, whereas deeply planted crowns produce fewer spears

SEEDLING TRANSPLANTS comparable in price, but crowns are one-year old plant material, whereas transplants are Transplanting seedlings into the field is an only 10 to 12 weeks old. Since the growing acceptable alternative to crown planting if season is short in Minnesota and transplants monitored closely. Seedlings are produced in do not grow to a large size in their first greenhouses and are usually transplanted season, transplants may come into harvest into permanent commercial fields when they up to a year later than crowns. are about 10 to 14 weeks old. The young seedlings can be mechanically transplanted, which reduces planting costs. Studies PEST MANAGEMENT indicate that survival rates are comparable to Insects those of crown plantings. The plant spacing Asparagus grown in Minnesota is relatively is the same as in crown planting (see Figure free of insect pests compared to many other 3). A transplant solution of 10-52-17 or 9-45- vegetable crops. The asparagus beetle (black 15 should be used at planting time. Follow with white markings) is the most common the manufacturer's recommendation for insect that attacks asparagus. Adult beetles, mixing. Each transplant should receive at which over-winter under debris along field least 4 oz. of transplant solution. For best edges, begin to move to asparagus as the results, irrigation should be applied if rainfall plants first emerge in spring. Beetles feed on is insufficient to maintain adequate soil the spears and glue rows of black eggs, moisture. Seedlings should be thoroughly usually on the tips. These eggs hatch in hardened off before field planting. Place the approximately one week and the fleshy, dark plants in a moderately shady location and gray larvae then move to the foliage on which keep them moist. After about three days, they feed. The larval stage lasts two to three transplant them to the field. In many cases, weeks, after which the larvae drop to the the asparagus fern will totally yellow and die; ground, burrow into the soil, and pupate this is normal. (cocoon stage). Two or three generations are Transplanting may take place either in the produced during the growing season in spring (early May) or in the fall (early to mid- Minnesota. September). While spring transplanting is The twelve-spotted asparagus beetle (orange more common, fall transplanting has proved with black spots) also may be present. Its life successful in Minnesota, and provides cycle is similar to that of the asparagus flexibility in the scheduling of both labor beetle, differing primarily in that the larvae demands and greenhouse space. Regardless feed on the developing berries. Consequently, of the timing, the transplants should be as spotted asparagus beetles cause relatively large and vigorous as the transplant minor damage to the spears or fern. equipment will allow, and without becoming When asparagus beetles are present at root bound in the original containers. harvest, they can cause extensive damage. Weed control is a challenge in the Early-season feeding by adult beetles causes transplanting of asparagus. Cultivation will a distorted "shepherd's crook" growth of the be necessary to fill in the furrows as the fern spear. The presence of eggs also renders the grows and as herbicides lose their residual spears unacceptable for market. activity. On nursery seedlings, defoliation of the The question of whether to use transplants plants by asparagus beetle larvae should be or crowns is still unanswered. They are monitored carefully; insecticides should be

sprayed if a field has 5-10 adults/100 crowns warm, humid conditions) all help to reduce or 2% of the spears have eggs. After harvest, aphid infestations. When populations are limited feeding by larvae on established increasing rapidly and biological control does plantings may be tolerated; treatment not appear to be effective, malathion threshold for adults increases to 5-10 (Cythion® 5E) should be used at 2 pints per adults/10 crowns. Several insecticides are acre. Sevin® is not recommended for aphid labeled for controlling asparagus beetles. control. Cultural controls for both species of beetles The asparagus aphid lays its eggs in late include following good cultural practices that summer or early fall. The eggs over-winter on promote plant vigor and thorough harvesting the fern and fall to the ground by spring. of spears to reduce the number of beetles Unharvested asparagus, which ferns out in that hatch in the spring. Chemical control of early spring, is highly susceptible to early adult beetles may have to be repeated, since aphid infestations because egg masses are the beetles emerge from overwintering sites allowed to hatch and the aphid's life cycle over an extended period. begins. Asparagus that is harvested into early summer is not at risk until the fern is One of the most devastating insect pest that allowed to develop. The aphid feeds only on attacks asparagus is the asparagus aphid the fern, not on asparagus spears. Removing (Brachycorynella asparagi). The aphid was asparagus fern in late fall after it has dried first reported in southern and central down greatly reduces potential aphid Minnesota in 1982. The asparagus aphid is a infestations the next year, but this is seldom minute, blue-green sucking insect that possible before the first snowfall. Cutworms usually feeds on asparagus fern. In the can cut off asparagus spears below ground process of feeding, it injects a toxin into the and even cause damage by feeding on the asparagus plant that is translocated down tips of spears above ground. Shoots damaged the stem into the dormant buds. The toxin by cutworm feeding develop into crooked causes the buds to elongate into new shoots spears and must be picked and culled. prematurely, producing a "witch's broom," or Chemical control is warranted if one or more a dwarfed, very bushy, short plant with worms/10 crowns are found. Pyrethroid silver, blue- green color. Under severe insect insecticides, particularly under cool, spring pressure, all the buds on the crown may conditions, will usually provide good "break," causing the plant to have none left cutworm control. Consult the over for the following season, essentially Midwest for the most up terminating the plant's life. Although the Vegetable Production Guide to date information which is revised each relationship between aphid infestations and year. economic damage is unknown, younger plants, including those 1-2 years after Weeds transplanting, are most susceptible to A number of herbicides are available for use damage. Several naturally occurring on asparagus. Depending on the type of biological controls usually prevent this aphid asparagus plantation (direct-seeded nursery, from reaching the damaging levels typically transplants, crowns, or established asparagus observed in the western production areas of beds), choosing the most effective herbicide California and Washington state. The adults and rate represents a challenge to the and larvae of several lady beetle species, grower. The desired herbicide should other insect predators, a parasitic wasp produce long-term weed control, be safe to (specific to aphids) and fungi (triggered by use on the asparagus fern, and be legal to

use. As outlined, each type of asparagus reduce the number of mechanical plantation presents a different set of cultivations needed to keep fields weed-free. problems. Established asparagus Direct-seeded asparagus Many herbicides are now labeled for use on Producing asparagus crowns in a nursery for established asparagus and can be applied eventual digging and establishment of new before the harvest begins (preemergence), production fields is still a popular practice. after harvest (delayed application), before The slow germination and emergence rate of and after harvest (split application), or asparagus seedlings and their slow growth throughout the harvest season (multiple rate present outstanding weed control application). The problems facing the grower problems. Therefore, the major weed control are choosing an application method that objective in nursery production of crowns complements the operation and choosing a should be to use an herbicide that has long chemical and rate that will control weeds weed-killing activity yet remains safe on the after harvest for the duration of the growing delicate asparagus seedlings. The herbicide season. should remain active at least until the seedlings are large enough to be Diseases There are several important diseases that can mechanically cultivated safely. This may take cause significant asparagus losses: Fusarium as long as two to three months after seeding. root and crown rot, rust, and Stemphylium Transplants purple spot. Refer to the Midwest Vegetable for the most up to date The use of seedling transplants to establish Production Guide new asparagus acreage is sometime used in recommendations on the use registered Minnesota. Since furrow opening and fungicides available to manage these planting is a one-step operation, herbicides diseases. to control weeds must be applied "over-the- Fusarium wilt root, and crown rots top" of the transplant fern or directed to the ground after planting to avoid the asparagus A common, soil-borne , Fusarium fern. Primary concerns include: selecting a moniliforme, is the cause of asparagus crown herbicide and a rate that is toxic enough to rot. The fungus is found in soil where control weed species but not seriously set asparagus is grown. Generic terms used to back the growth of the asparagus plant, and describe asparagus crown rot are seedling determining the application method. blight, decline disease, and replant problems. A second Fusarium disease, caused Crowns by Fusarium oxysporum f. sp. asparagi, Traditionally, most new asparagus causes root rot, wilt, and seedling blight. This production fields are established by planting pathogen causes the water conducting one-year-old nursery grown asparagus vessels to plug, producing wilting of spears crowns into deep furrows. Since the first new and ferns. shoots may take many weeks to emerge and Infection commonly occurs when Fusarium grow to a size that can be cultivated, weeds moniliforme enters the roots and spreads in the furrow may become large and not throughout the plant. Symptoms of controllable by cultivation. Therefore, an asparagus crown rot include wilting of easily applied pre-emergence herbicide of mature plants during hot summer weather, long, dependable activity is necessary to stunting, yellowing, seedling blight, and

death. Infected areas of the crown turn plants and predispose them to disease. Once brownish in color as cells that transport Fusarium becomes established in the field, water and nutrients become clogged due to there are no simple controls. Since the the infection. Cutting open affected plants pathogen is soil-borne, new beds should reveals dark, reddish-brown colored decay of never be planted in fields previously in lower stems, crowns, and roots. Later, asparagus. portions of the crown begin to dry up until the entire plant dies. Scattered wilting Asparagus rust throughout the fernstalks is more indicative Asparagus rust, caused by asparagi, of Fusarium oxysporum f. sp. asparagi; occurs in varying amounts wherever the Symptoms caused by this disease usually plant is grown, and attacks asparagus ferns occur midsummer when 1 or 2 fernstalks per during and after the cutting season. In plant turn yellow. This leads to large gaps in addition to asparagus, Allium species, such the asparagus field and significantly lowers as cooking and , are also crop production. Fusarium-infected plants susceptible. There are no alternate hosts increase in number until the crop is too such as is common with other Puccinia rusts. sparse to harvest economically. The positive Asparagus spears are usually harvested diagnosis of Fusarium moniliforme is based before extensive rust symptoms appear. on laboratory detection of the fungus Symptoms are first noticeable on the growing associated with typical symptoms on the shoots in early summer as light green, oval plant. lesions, followed by tan blister spots and Fusarium moniliforme survives in crown and black, protruding blisters later in the season. stem lesions of diseased, old asparagus The lesions are symptoms of Puccinia plantings. Fungal spores are spread by air asparagi during early spring, mid-summer currents and on the surface of contaminated and later summer to fall. Severe rust asparagus seeds. infections stunt or kill young asparagus shoots, causing foliage to fall prematurely, Fusarium diseases are extremely difficult to and reduce the ability of the plant to store manage once the fungus is established in an food reserves in the crown. asparagus field. Primary controls are choosing healthy, Fusarium-tolerant varieties The orange spores are the key sign for this of plants obtained from a reputable source, disease. Run your hand over an asparagus and planting in fields not previously used for spear and examine your palm for orange- asparagus. Fusarium-resistant varieties for colored spores. Laboratory techniques may Minnesota growers include Jersey Giant, also be used for diagnosis of asparagus rust. Jersey, Knight, Jersey Prince, and Viking KB3. Spores overwinter on host plant residue, Disease intensity can be increased by germinate in early spring, and produce new nutrient stress, drought, and insect damage. infections on growing asparagus spears. The To help minimize losses due to these light green, oval lesions are surrounded by a diseases and to establish a vigorous concentric ring pattern. In young plantings, asparagus field, only disease free plants before stalks are harvested, lesions develop should be planted on well-drained soil. Soil yellow spore-bearing structures in concentric pH should be maintained between 6.5 and 7.5 rings. Wind and splashing rain can spread with moderate levels of fertility. To minimize spores to branches and fern needles, where disease, control pests, diseases, weeds, and avoiding excessive harvesting that stresses

they germinate in the presence of water debris from the previous season into the soil drops. in the fall results in less disease severity than when debris is left on the soil surface. Plants affected by rust are more susceptible Volunteer asparagus seedlings can become to Fusarium crown and root rot. infected during the harvest season and may Plant rust-resistant varieties of asparagus, serve as a source for disease increase as well such as Jersey Giant or Viking KB3 which are as reservoir to carry the disease from the reported to grow well in Minnesota. Remove harvest period when the spears are removed volunteer asparagus within 300 meters of to when the ferns are allowed to commercial plants, and locate new plants grow. Research from Michigan State has away from established fields. Plant well- determined that the Tom-Cast disease spaced rows oriented in the direction of forecaster alerts growers as to when prevailing winds to maximize air movement environmental conditions are favorable for and facilitate drying after rain. It is important purple spot disease development (extended to note that plants affected by rust are more dew, and rainy periods coupled with high susceptible to Fusarium crown and root rot. humidity and warm temperatures) and to Several growers are using the culture practice when fungicides are necessary. In these of increasing the row width from four to five studies, incorporation of the Tom-Cast feet to allow more air movement around the disease forecaster enabled growers to reduce plants therefore allowing the plants to dry fungicides while still successfully managing out earlier from rains or heavy dews. purple spot disease of asparagus. Labeled Fungicides: Timely fungicide applications will provide reasonably good Postharvest, handling, and storage control of rust. During periods of high Pack asparagus upright with damp absorbent humidity and extended rainfall, applications pads under the spears. Asparagus spears will should be made every seven to ten days. bend toward light, so horizontally packed spears will noticeably bend upwards. Do not Stemphylium purple spot keep spears in pans of water for very long, or Stemphylium purple spot, caused microbial infection can occur. Cool spears by Stemphylium vesicarium, was first found immediately after harvest to prevent in Minnesota asparagus fields in 1988. bacterial soft rot infection. Store asparagus for up to 3 weeks at 36° F. Asparagus will Symptoms on the spears appear as elliptical turn flaccid and dull gray-green if kept for sunken, purplish spots, which may cause more than 10 days at 32° F. Avoid exposure rejection of product. The disease produces to ethylene gas, as ethylene can cause brown to tan lesions with dark purple toughening of spears. margins on the ferns. In spring, spore are produced from last year's infected plants and HARVESTING spread by wind and water to newly developing plants. Infection occurs through Preparing for harvest natural openings and wounds on current In earliest spring. mow or chop the old season asparagus tissue with favorable asparagus fern with a brush hog mower or temperatures and moisture from rainfall or flail chopper. Add phosphorus and irrigation. potassium fertilizers and give the entire field a shallow disking. Do not delay disking. Good sanitation is the key to good disease Doing so can cause considerable damage to management, and incorporation of asparagus

the developing but unemerged spears just begin the following season, although the below the soil surface. Wounds also provide a harvest should be terminated immediately portal for disease organisms. any time spears are reduced to pencil size. Harvesting may have to be performed every Apply a preharvest herbicide at this time. two days at the height of the harvest season. The advantage of an early season herbicide Spear emergence greatly increases in application is that it reduces or even response to warm temperatures and slows prevents the establishment of winter annuals considerably with cold temperatures. and other weeds not controlled by cultivation. Overharvesting greatly reduces the vigor of the asparagus plant by seriously draining the Harvest sugar reserves in the crown. Remember: next Spears are hand harvested when they are six year's yields and profits are determined by to eight inches long. A special pronged knife how well the asparagus is treated this year. can be used to cut the spears below the soil surface. or they may be snapped at the soil Field maintenance after harvest surface. Cutting must be done carefully to Asparagus plants need stored nutrients and avoid damaging developing spears and the time to recover from harvests. They also crown below the soil surface. The knife need weed-free environments, moderate soil should be placed near the spear, tilted on a fertility, and adequate moisture to build up 45 degree angle, and directed to cut the food reserves in their crowns. Neglecting spear about two inches below the soil asparagus fields after harvest is a more surface. Shoots injured by cutting will not significant contributor to poor yields in develop properly and should be culled. subsequent years than insect or disease Spears may be hand snapped just above the damage. soil surface. Snapping severs the spear at the After harvest, add nitrogen fertilizers junction between the green tender tissue according to soil test results. Since the generally above ground and the white woody asparagus plants will now be left to fern out, tissue below ground. The advantage to they need nitrogen to encourage maximum cutting spears is that the woody base fern development, photosynthesis and restricts water loss, which preserves spear storage of sugars in the roots for next year's quality. crop. Research has consistently shown that Depending on the planting method, the bushier the asparagus plant the better asparagus beds require two to three seasons the yields will be the next season. Nitrogen to become established. Transplants and should be incorporated very shallow. A crowns require two years for establishment postharvest herbicide application is before first harvest begins, whereas necessary to extend weed control full season. asparagus started from seed takes three full A contact herbicide may be necessary to kill growing seasons before harvest. During the perennial weeds prior to fertilizer establishment years, fern growth, plant vigor, incorporation. In times of severe drought or and health should be optimized with careful if the asparagus is grown on sandy soils, use cultural management. For areas with short irrigation to maximize subsequent yields. growing seasons, the USDA recommends a Asparagus is a rewarding crop to grow. But it light harvest (two to three weeks) during the is a perennial plant that will cause perennial first season after plant establishment. A full problems if its culture and maintenance harvest season of six to eight weeks may schedules are ignored.