TURNIP Brassica rapa

FAMILY CHARACTERISTICS
    Brassica rapa is a member of the Brassicaceae or Mustard Green family. The crops within this family prefer cool seasons and have a wide diversity of life cycles, such as annuals, biennials, and perennials as well as a diversity among flowering habit for instance, hermaphroditic, actinomorphic, and hypogynous.  Other members within the Brassica family that are popular vegetables today include broccoli, cabbage, cauliflower, kohlrabi, brussels sprouts, Chinese cabbage, broccoli raab, and rhutabagars and varieties of each deviate as well due to their unique uses and world wide importance. These vegetables are utilized for medicines, desserts and pies, snack food, refreshing salads, adornment, and enticing vegetable entrees.
    Family members include:
        Armoracia rusticana Gaertn., Mey., Scherb.; Horseradish
        Barbarea vema (Mill.) Aschers; Upland Cress
        Brassica carinata A. Br.; Abyssinian Mustard
        Brassica campestris L. (Chinese group); Pak-Choi,  Chinese Mustard,  Celery Mustard
        Brassica campestris L. (Pekinensis group); Pe Tsai,  Chinese Cabbage,  Celery Cabbage
        Brassica campestris L. (Perviridis group); Spinach Mustard,  Tendergreen Mustard
        Brassica campestris L. (Rapifera group); Turnip
        Brassica campestris L. (Ruvo group); Broccoli Raab,  Rapa,  Italian Turnip
        Brassica juncea (L.) Czern. & Coss.; Leaf,  Brown and Indian Mustard
        Brassica napus L. (Napobrassica group); Rutabaga,  Swede,  Swede Turnip
        Brassica napus L. (Pabularia group); Siberian Kale,  Hanover Salad
        Brassica nigra Koch.; Black Mustard
        Brassica oleracea var. acephala D.C.; Collards, Scotch Kale
        Brassica oleracea var . botrytis L .; Cauliflower
        Brassica oleracea var. capitata L.; Cabbage
        Brassica oleracea var. fruticoca Metz.; Thousand-headed Kale
        Brassica oleracea var. gemmifera, D.C.; Brussel Sprouts
        Brassica oleracea var. gongylodes L.; Kohlrabi
        Brassica oleracea var. italica Plenck.; Broccoli
        Crambe maritima L.; Sea Kale
        Eruca sativa Mill.; Roquette or Rocket Cross
        Lepidium meyenni Walp.; Maca
        Lepidium sativum L.; Land Cress,  Pepper Grass
        Raphanus caudatus L.; Rat-tail Radish
        Raphanus sativus L.; Radish
        Raphanus sativus L. (Longipinnatus group); Daikon or Chinese Radish
        Rorippa nasturtium-aquatkum (L. ) Hayek; Water Cress

CROP HISTORY AND DEVELOPMENT
     The turnip at one time was hailed as the vegetable of the nobility.  The turnip has been considered a source of food for man and animals in both ancient and modern civilizations. Native to western Asia, the turnip is grown today in the United States, Asia and Europe.  The turnip, which was actually used for trading in young colonies, has been grown in America since 1622 in Massachusetts. The Indian turnip was grown for its seeds, which produced Colza oil, used to fill lamps in Europe during the 13th century. The turnip has also been used as a natural medicine treating measles, cancer, small pox, chilblains and gout. The turnip was even fermented for an alcoholic beverage in early centuries.  European farmers were introduced to a variety called the "stubble turnip" during the 17th and 18th century, which lead to the period known as the “Age of the Turnip.”  The turnip has been mentioned with admiration by Robinson Crusoe, as well as Thomas Jefferson who grew several varieties on his plantation.

PLANT CHARACTERISTICS
     Brassica rapa, is a  biennial (life cycle completion is within two seasons) cool season crop, and  is one of the most commonly grown and widely adapted root crops today. Cool nights slow down the respiration rate which increases the quantity of stored carbohydrates to provide a richer tasting turnip. Turnips are grown for their roots and leafy tops. Turnips are a deep rooting species, the root can be long, round or flat, white, pink or yellow. Erratic growth encourages a strong flavor and woody fibrous growth and the turnip will become bitter if the weather is too warm or dry, while a steady rapid growth promotes a sweet tender flesh. Turnip leaves are thin, light green to dark green, pubescent, lyrate pinnatifid with a length of 25-55cm. Glaucous stem leaves are accompanied by an elapsing base.
    Turnip flowers are bright yellow, inflorescence  with spreading sepals.  Petals in anthesis are confined and commonly tower above unopened buds.  The outer 2 stamens are bent outward at the base and stunted compared to the inner stamens. Seeds  are blackish to reddish brown and globular in shape. Turnip is a short season crop which bolts if temperatures fall below 50°F for 3-6 weeks.  Turnips require a cold damp climate to reach perfection.

Cultivars There are numerous varieties of Brassica rapa available, which provide the most productive utilization.  Color variations of the root can be white, yellow, red and pink skins, and white or yellow flesh and the shape of the root can be long, round, or flat.  The most crucial when choosing a variety is determining what the use for the turnip will be.  Whether you want to grow the turnip for its leafy greens, or swollen base, a late season crop, or an early season crop. 'Royal  Globe 2', 'Royal Crown', 'Shogoin Topper', and 'Tokyo Cross' are all grown for their roots, while 'Shogoin', '7 top', 'Topper' and 'All Top' are grown for their leaves.  The future of the vegetable turnip is promising with varietial development focusing on modifing current types to the production of vigorous and unvarying  growth.

Tokyo cross variety

PROPAGATION METHODS
    Propagated by seed, turnips may be sown thinly in spring, summer, or drilled into rows as is generally done in fall plantings.. Most commonly in Georgia, the turnip is grown when the temperature resides below 24°C.  Seeds may be broadcast on fertile, well prepared seedbeds. Growing  a turnip after another root crop promotes disease.  Rotation between non root crops is advised for control of diseases. Using hot water treated seed and fungicide treated seed protect against soil borne diseases as well.  Seedling emergence occurs within 3 days based on ½ inch deep planting if the temperature is at 59°F. Turnip seed weight contains 15,000 seed per oz with a minimum field germination of 80% expected.  Seedlings will germinate with moisture levels slightly above the permanent wilting point.
    Optimum temperature for best growth and quality of Brassica rapa is between 60-65°F.  Traditional spacing for turnips grown for their roots is 2-6 inches and greens 1-4”.  Distance between rows for drilled seeds is 12-36” for best root growth and 6-12 inches for greens. Most commonly a grower will overseed and then thin the crop for best growth. Field seeding is recommended at 1-2 lbs/acre.  Multiple rows of raised seedbeds will increase production efficiency per unit of land, and seedbeds can range from 3-5 feet wide. For the Coastal Plain recommended seeding for spring is Feb1-April 15 and Fall is Aug. 1- Sep 15.  For the Piedmont area Feb 15-Apr. 30 in the spring and July 15-Sep 15 in the fall.  If extended periods of cold weather occur, spring planted turnips well along in development may form seedstalks rendering them ineffectual.
    Pollination Cross pollination by a diversity of insects is indispensable for fruitful seed production.  2-3 bee hives are adequate to secure pollination and to safeguard seed set.
    Thinning Thinning turnips in a field is a tedious task, and is normally not needed,  however,  thinning the crop 3 to 4 inches apart in the row to increase growth and vigor may be warranted.

CULTURAL PRACTICES
    Overview Under optimum growing conditions early varieties will mature in 40 days and late varieties in 75 days.  A deep loam or sandy loam soil type are recommended with good drainage, and a fair amount of organic matter.   The pH should remain between between 6.0 and 6.8 and limed if needed.  Turnip will fail to make large roots if it is too crowded and should be space at least 2-3” apart.
    Soil A crop such as the turnip that is grown for its roots, requires a lose friable soil at all times during root development.  Hard, heavy soils will promote disfigured roots.  Turnips are extremely deep rooted plants and require deep, open soils for root penetration deep into the soil. A preferred pH is between 6.0 and 6.8, however turnips can withstand a pH as high as 7.5.
    Temperature The turnip is a cool season biennial and prefers temperatures between 60 and 65°F for optimum growth.
    Irrigation An abundant reserve of moisture is required  to guarantee a high quality product. An adequate measure of moisture is approximately 1.5 inches of water every 7 to 10 days.  Drip irrigation is used in small productions schemes, decreasing  the amount of moisture accumulating on turnip leaves  that promote disease development on the foliage.  However, drip irrigation has not been proven to be an economical method for common field production. Irrigation methods include overhead systems such as a center pivot, or traveling gun.  Irrigation scheduling, using a tensiometer, can determine the current available soil moisture and amount needed to grow a successful crop.  It is important for adequate moisture to supply the plant during all stages of development for proper root growth and leaf expansion.
    Weeds Weeds can be detrimental to the growth of a crop, young or old.  Cultural practices of weed control include; shallow cultivation,  use of pre and post hervbicides and, cleaning equipment after use.
    Pruning For the home grower removal of misshapen, or discolored leaves would decrease disease and increase the aesthetic value of the plant, however for commercial production pruning is not economical.

INSECTS
    The Brassica family have a number of insects interconnected among each crop.  Turnip aphids, Red Turnip Beetle, White Fringed Beetle, Imported Cabbage Worm, Wire Worm and Harlequin Bug, and Turnip gall weevil are among the most important insects which can damage the turnip crop.  It is extremely important that constant scouting is used to decrease the number of pests in a field, as well as to determine the areas where control is needed.
    Red Turnip Beetle- Entomoscelis americana ia brown and similar to a Cabbage Aphid, but is not covered by a white wax. Are insects which move in bulk and feed in colonies underneath the leaves.  Signs that this insect is attacking a turnip include curled leaves and an overall yellow appearance on the plant. A dusting application or a spray of malthion every 7-10 days will increase control. Late fall to early spring, cultivating the field will bury eggs and  reduce larval survival.  Cultivating in the early spring removes cruciferous weeds, which destroys food for larvae.
    Flea Beetle-Phyllotreta striola feeds upon the leaves of the turnip, causing a loss of photosynthetic components within the leaf.
    Imported Cabbage Worm- Throughout the seasons butterflies may be seen hovering over the foliage of a turnip crop.  These butterflies are using the foliage as a nest to deposit their eggs.
    Vegetable Weevil- The vegetable weevil feeds upon the root source of a crop gorging upon nutrients intended for the crop.  As nutrients and water are being depleted from the root zone the crop begins to wilt.

DISEASES
    As for insects, diseases in a field can be detrimental to a market and a food reserve.  Scouting is again necessary to determine the areas where disease are prevalent and the control needed as well as,  to decrease the number of outbreaks.  There are numerous diseases which affect turnips.
    Black Rot- caused by Xanthomonas compestris pv. campestris. This disease affects the above ground portion of the crop but may also affect the roots.  Roots which are affected are known to develop dry rot, leading to upmost devistation of a crop.  Signs of this disease include dwarfing of young seedlings, and lower leaf drop, a V shaped pattern will form on the leaves and as the disease progresses to the to the midrib of the leaf it causes the veins to turn black, thus the infected portion becomes brown and dry. The best means of control is using bacteria free seed.  Using seed treated by hot water treatments and spraying the crop with a fungicide at 7-10 day intervals will decrease the possible spread of the disease.
    Root Knot Nematodes- Meloidogyne spp.   Root knot nematodes invade the root portion of the crop causing infected roots to swell at the invasion point and develop knot gall. Above ground symptoms such as decreasing growth, and wilting yellow leaves.  Overall the plant dies prematurely.  Chemical treatments with a nematicide fumigant is the best possible means of control.
    Clubroot- Plasmodiophora brassicae is one of the most serious soilborne diseases of the Brassica family, especially detrimental in soils which are acidic. As soil temperatures rise the disease becomes more aggressive. Disease offspring known as zoospores enter into the plant by its roots, through either parasitic wounds or mechanical wounds. A club like or knot like structure is formed at the roots where extreme cell malformation has occurred.  Symptoms appear as continual wilting and then recovery, eventually the plant does not recover and thus dies.  Rotation with nonsucceptible crops, sanitation, and disinfecting equipment, and a pH above 7.3 discourage the disease.
    Fusarium Wilt-Fusarium oxysporum F.sp spinaclae is a seedborne and soilborne fungus that is common if soil temperature is warm. The main symptom of the disease is a vascular discoloration in crown area. Other symptoms include pale green and leafy margins, a  rolling of leaves inward as the plant then wilts and dies. Treated seed and field rotation are the best methods of control for this disease.
    Downy Mildew- Peronospora parasitica Penetrates the vegetative growth between leaf cells as the disease spreads.  Disproportionate, purple spots begin developing on leaves, and stems, these enlarging spots becoming yellow brown. A  mildew forms and grows under  the leaf surface. Overwintering structures can be found on plants or in infected plant debris.  Humid coastal regions are a haven for this disease which can cause damage to young plants and transit crops. Extremely moist and temperatures between 50-60 degrees°F can encourage this disease.  Crop rotation, and fall plow will decrease incidence.
    Black leg- Phoma lingam. Survival is within seed and infected plant debris.  Infected seed germinate causing a fungus to grow quickly infecting the seedlings causing lesions, and stunting of overall growth. Rainfall and irrigation can spread the disease from a diseased plant to a healthy plant.
    Turnip Yellow Mosaic virus is transmitted by over 50 different species of aphids. Symptoms of this virus include black necrotic spots, leaf distortion, stunting, mosaics, and mottling.

HARVESTING
    The appropriate size for harvesting a turnip root occurring between 45-80 days.  Roots of the turnip are lifted from the soil which is normally allowed to dry prior to harvest so they are pulled with ease, topped, rinsed and cooled. Handling the roots carefully is important to decrease damage and rot during storage.  The turnip is marketed quickly as it is not suited for storage. Turnip greens are normally harvested when the crop is young and tender. For turnips that are going to be processed, mechanical harvesting equipment such as that used on carrots may be used.  Turnips that are topped are sold to the general market by the hundred bushel. In well drained soils, pits and piles can be used for storage however, piles should not be too wide nor too deep to prevent warming at the center.  Production floors that are cool provide adequate area for indoor storage piles or containers. Storage temperature  in cold storage should remain between  0 and 1.5°C with a relative humidity of 90-95%.  Polyethylene vented bags are often used to seal in freshness.  Waxing of turnips is not recommended for extending the storage period.  Paraffin wax that is normally used to improve appearance and retain moisture may cause injury from internal breakdown.
 

Hand harvesting turnip greens

Harvested turnip greens

Harvested turnips for fresh market

Harvested turnips for processing

 

Waxed turnip root

Turnip root plus top