CARROT Daucus carota var sativus

FAMILY CHARACTERISTICS
    Daucus carota var sativus  (Carrots) are grown for their prominent root structure and characteristic flavor and color.
    Carrots are grown as a cool season vegetable.  Production of the enlarged hypocotyl occurs most significantly when cool nights slow the plant respiration, allowing for an accumulation of carbohydrates.
    Of all root crops, D. carota var sativus is considered the most important.  High Vitamin A, mineral and dietary fiber content of carrots contributes to their importance as a major food crop utilized in our diet.
    Other members of the carrot family include:
        Anthriscus cerefolium Hoffm.; Chervil
        Apium graveobus L. var. duke, Pers.; Celery
        Apium graveobus L. var. rapaceum, DC.; Celeriac
        Arracacia xanthonhiza Bancroft.; Arracacha
        Chaerophyllum bulbosum L.; Turnip-rooted Chervil
        Ferula communis L.; Fennel
        Foeniculum volgare Mill . var. dulce Fion; Florence Fennel
        Pastinaca sativa L.; Parsnip
        Petroselinum crispum (Mill . ) Nym.; Parsley
        Petroselinum cripum (Mill.) Nym. var. tuberosum; Turnip-rooted Parsley

CROP HISTORY AND DEVELOPMENT
    Originally from Middle Asia, D. carota var sativus spread east and west, being cultivated in Europe as early as 1000 BC  where it was grown as a medicinal plant, used to treat stomach problems, wounds, ulcers, liver and kidney ailments. Production as a food crop began in 600 AD in the region now known as Afghanistan. The first cultivated carrots were large and woody textured with a purple color. Yellow types (perhaps originating as anthocyanin-free mutants) were selected and cultured in Syria and Turkey in the ninth or 10th century; then spread to China in the late 13th century and to Europe in the 14th century.
    Carrots are grown primarily for fresh consumption in salads, hors d'oeuvres, and as snacks and meal accompaniments. They are used in the preparation of soups, stews, curries, pies and, tender roots may be pickled. Certain varieties of carrots have been used as feed for horses and dairy cattle.
    Wild  related type of carrots are found from the British Isles to NW China.  Wild carrots produce white roots with less aromatic qualities than the cultivated types.  These wild types of D. carota  readily cross-pollinate with the cultivated variety D. carota var sativus.  Only one interspecific cross has been reported:  D. carota  with D. capillifolius.
    Yellow and purple varieties of D. carota var sativus were grown in Europe until the 17th century when the orange varieties were developed in Holland.  The modern Western carrot came out of Holland in the late 18th century:  ‘Long Orange,’ ‘Late Half Long,’ ‘Early Half Long,’ and ‘Early Scarlet Horn.’ American settlers brought these orange varieties with them and the orange typed replaced the yellow varieties brought to Virginia in the 1600’s.
    Breeding work with D. carota var sativus has produced plants of increased disease and pest resistance. Selection has focused on reducing the size of the xylem and increasing the width and sweetness of the phloem, as well as different lengths and overall diameters.  There are four primary varieties grown in the United States:  Imperator, the most common grown for commercial fresh and “cut and peel” market, are 8-10 inches long, slender and tapered, having a small core and deep orange color; Nantes, primarily grown for home and local markets, are 6-7 inches long, 1-2 inches in diameter, cylindrical, and have excellent color and quality; Danvers (the “half long” carrot), used in both the commercial fresh market and processing industry, are 6-7 inches long, 2-2 ½  inches diameter, conical, and have excellent quality  but become woody as they age; and Chantenay, used primarily for processing, are 4½ -5½  inches long, 2-2½ inches at the shoulder tapering to a point, is lighter in color than other types, and has a coarser texture than others, lending itself to not be preferred for fresh consumption, but rather for storage or processing.
    Amsterdam or Miniature carrots are the true “baby carrot.”  They are expensive to produce, and are mainly sold to specialty markets and restaurants.
    Of each of these primary types, there are many variations:

Nantes	Imperator	Danvers	Chantenay
Protégé	Apache	Bolero	Gold King
Presto	Navajo	Eagle	Convert
Nanco	Blaze	Goliath	Condor
Nassau	Six Pak II		Red Cored
Primo	Choctaw

    The US ranks among the top nations in the production of carrots:  fourth in acreage and volume, third in terms of yield (31.7 tons/ha). Russia, Japan, France, and the United Kingdom are also leading producers. World wide 13.37 MT were produced in 1990, a 30% increase over the past decade.

PLANT CHARACTERISTICS
    Overview D. carota var sativus is a herbaceous biennial plant grown as an annual. In the first year, seedlings emerge with two strap-like leaves which are the cotyledons, followed by rosettes of doubly compound leaves arising from the crown. From the hypocotyl, a tap root develops.
    Initially, the plant produces top growth, which supplies carbohydrates to the swelling hypocotyl. High temperatures increase respiration in the leaves which reduces color development and sugar accumulation. Low temperature initiates flower development and reduces carbohydrate accumulation in the hypocotyl.
    Most often, the plant will not initiate a flower head until the second year of growth and a chilling period.  The inflorescence is an umbel, with individual flowers maturing at staggering intervals.  Cross-pollination is essential for seed development.  The Apiaceae family derives its name from its affinity for attracting bees, which are the primary pollinator.
    D. carota seeds are tiny, and are covered with a fleshy mericarp that must be removed prior to seeding.  Due to cross-pollination,  variablility is great in plants.
    Root System A tap root system develops from the hypocotyl with secondary lateral roots branching from the xylem.  Together, the hypocotyl and the tap root form the ‘Carrot Root'. At the center of the root is the light colored and more woody xylem surrounded by the deep orange and sugar loaded phloem. The periderm skin is composed of suberin and other waxy substances. Optimum root growth occurs at 60-70°F.  Temperatures into the 50’s will affect the color development and favor longer, more slender roots. Temperatures above 70°F will cause shorter, thicker roots with a stronger flavor, but less sugar.
    During flower initiation, the hypocotyl crown shrinks as carbohydrates and water content is shifted to support flower development and the overall root diameter becomes slender.
    Leaves  A tight rosette of leaves arises from the crown after the emergence of the characteristic cotyledonary leaves. Two kinds of leaves are formed.  The lower leaves are pinnate and linear or lanceolet, and are fine and lacy in appearance.  The upper leaves are smaller and less divided.
 Leaves in the second year of growth arise from the crown and along the elongated stem.
    Flower Vernalization of the plant or seed induces formation of the inflorescence. Vernalization period is up to 6 to 8 weeks at temperatures below 50°F. Several cycles of flowering occur, producing umbel shaped inflorescence.  The first inflorescence is the largest, and is termed the king umbel, followed by the queen and other secondary umbels.  The white flowers are perfect,  and require cross-pollination for seed set.  Male sterile hybrids are often used as a seed source to decrease variability.
    Seed Seeds are formed from carpels.  They are tiny and covered with a spiny, hooked, and slightly curved mericarp. The mericarp contains a characteristic oil which inhibits seed germination, requiring the removal of the mericarp before planting.
    Seeds are highly variable due to cross-pollination and have undergone extensive breeding programs to increase uniformity.  Hybridization, however, has not produced consistent results.
    Seed development and vigor are determined by the conditions under which they are formed.  A larger seed (embryo) will have a more rapid emergence and produce a stronger seedling. This is important in that the seed is slow to germinate and the young seedling is slow in the initial growth phase. There are approximately 23,000 seeds per ounce.

PROPAGATION METHODS
    Overview  Root crops are direct seeded.  Transplanting carrots disturbs the tap root and prohibits proper hypocotyl root development.  Seeds can be drilled ( ½ “) or broadcast in the field at a rate of 2-4 lbs per acre. At a temperature of 68°F, seeds should germinate in 7 days.  Cooler temperatures extend the germination process. Seeds may remain viable for 3 years with up to 85% germination.   In selecting seed, it is best to obtain seeds which have been cleaned (mericarp completely removed), and which are large and viable.  High quality grade and fungicide treated seed will ensure a more uniform stand.
    Pelleting of seeds with materials to respond to particular environmental conditions (moisture) or planting equipment  may be useful in improving size and uniformity.
    Appropriate seeding equipment promotes a more uniform crop by precise seed placement.
    Seeds for commercial use are produced primarily in dry regions of Washington.  However, seed producers are also located in major carrot growing areas.

CULTURAL PRACTICES
    Overview D. carota var sativus can be grown in a wide variety of deep, loose, friable soils at cool to moderately warm temperatures.
    Seeds are planted in raised beds or flat rows.  The fertility program should pay close attention to maintaining high levels of  phosphorus and potassium during the growth cycle. Weed control is very important throughout growth.  Soil moisture should be held constant throughout the growth cycle, with at least 1½” water per week and more if grown in an arid region or in a sandy soil.
    Soil Type  Carrots grow well on most deep, friable soils.  Muck and sandy loams are highly desired for carrot production.  To produce quality carrots, all clods, hard lumps, plant debris, and the like should be removed from the soil to prevent forking or root stunting  from occuring. A soil pH of 5.5 –6.5 is optimal.
    Crop stands are often planted in raised beds at least 4” high on 20 – 40” centers 12-15” apart with a stand of 10-20 plants per foot for dicing carrots and 20-30 plants per foot of row for fresh market carrots.  Many growers using precision planters have three row seeding configurations centered on the beds.
    Temperature Carrots are a cool season crop, having optimal growth between 60-65°F, with a minimum of 45°F and a maximum of 75°F.    Crops to be grown in the fall can be started in the heat of late summer to ensure that a substantial period of cool weather exists before frost.
    Color development is determined by temperature.  Maximum color development occurs in the 60-75°F optimal growth range.  Temperatures higher or lower will cause a lighter root color.  Temperatures over 70°F will also reduce root length, while temperatures below 60°F will produce longer roots.
    Fertility A lime application is made for mineral soils below pH 5.8 and organic soils below 5.4. As with most root crops, carrots are heavy phosphorus and potassium feeders.  A deficiency of potassium reduces root quality and overall plant metabolism.  Phosphorus is also required in significantly higher amounts than other vegetables.  The amount of nitrogen required by carrots is generally lower than that of potassium.
    Fertilizer recommendations will vary according to soil type, variety, and the production season.  Foliar analysis throughout the growing season will most accurately determine fertilizer requirements.  Sufficient nutrient levels in mature leaves from new growth in the middle of the growing season are as follows:
 

Macro	N	P	K	Ca	Mg
	----	----	-%-	---	---
Low	2.1	0.2	2.5	1.4	0.3
Suffic	3.5	0.5	4.3	3.0	3.0

 

Micro	Fe	Mn	B	Cu	Zn	Mo
	----	----	ppm	----	----	----
Low	50	60	30	5	25	0.5
Suffic	350	300	100	15	250	1.5

    General fertilizer recommendations for muck soils include a relatively low application of nitrogen, 50 to 75 lb per acre; 50 to 100 lb per acre of phosphorus; and 50-200 lb per acre of potassium. Mineral soils require a heavier application:  150 lb per acre nitrogen, 100 lb per acre phosphorus, and 250 lb per acre potassium.
    Carrots respond best to fertilizer banded to the side and below seed. Where raised beds are utilized, broadcasting fertilizer is often employed. A split application of nitrogen applied as a side dressing 6 weeks after planting  prevents excessive N-uptake which promotes excessive vegetative growth and delays root development.
    Weed Control Weeds can create stressful competition for young seedling growth and nutrient uptake.  Commercially, herbicides are the primary means of weed control.  The rate and timing of chemicals is important. Appropriate use of herbicides can reduce plant losses due to weed competition.
    Irrigation Constant moisture levels promote the production of quality carrots of uniform size.  Calcium deficiency disorders such as root cavity spots are reduced with a constant level of soil moisture moving available calcium into the plant. Irrigation of the field at the time of seeding enhances germination and stand establishment.
    The use of overhead sprinklers should be limited or utilized in a way that reduces foliar diseases.
    Furrow irrigation is used with raised beds on soils where water percolation is good.

INSECTS
    Carrot Weevil ( Listronotus oregonensis) The white, legless larvae of this insect cause damage to the roots through feeding in zig-zag grooves and tunnels.  Roots become unmarketable, and eventually, the carrots wilt and die.
    Biological control using the egg parasite Anaphes sordudatys provides significant control.  Such parasites can be encouraged through the planting of certain weeds around the border.
    Crop rotation and removal of infected plants are effective methods of reducing weevil pressure.
    Carrot Caterpillar (Papilio polyxenes) This large, 2” long larvae is green with black cross band on each segment and six yellow spots on the front margin.  Two to three generations can proliferate each year.  Substantial damage may occur.
    Aster Leafhopper (Macrosteles divisus) Leafhoppers are green,  1/8” long, soft bodied, sap sucking insects.  They cause plant distortion or burned leaves, and are vectors for various diseases.
    Removal of weeds such as wild carrot, pineappleweed, and plantain provides some control.
    Carrot Rust Fly (Psila rosea)  The yellowish-white larvae of this fly tunnel into roots creating mechanical damage and providing an entry for root rot pathogens.  The adults are shiny and dark with a yellow head.  They lay their eggs in the soil near the base of the plant.  In the northern states, late seeding often avoids 1st generation damage. The removal of culls and infected plants from the field helps to avoid future infestations.

DISEASES
    Leaf Blight (Alternaria sp and Cercospora carotae)  Alternaria is a fungus appearing later in the season on older tissue; C. carotae appears earlier on younger tissue.  They are noticeable on the foliage as causing yellowing and small dark brown elongated to round lesions.  The fungi over winter on crop debris and seed.
    Disease resistant varieties are available where disease pressures are great.  Crop rotation is also a recommended control if disease pressures prevail.
    Planting of ridges may also improve air circulation and reduce disease development.
    Violet Root Rot (Alternaria radicina [fungus] and Erwinia carotovora  [bacterial]) Root rots are more serious as storage diseases than field.  This fungus attacks the roots and foliage.  Root lesions appear as irregular to circular dark green to black cavitations showing some surface sporulation .  Rots caused by E. carotovora  have a characteristic odor and slime that develop rapidly under certain storage conditions.
    Proper storage conditions (temperature and relative humidity) minimize storage rotting.
    Aster Yellows The causal agent is a mycoplasm spread by leafhoppers.  Initial symptoms include yellowing and occasional vein clearing.  Witches brooming effect is present at the crown characterized by increasing formation of petioles. Roots become woody and form many adventitious roots.
    Leafhopper control is the most effective control of yellows.  Removal of nearby plants and infield weeds is also essential for inoculum reduction.
    Rusty Root and Cavity Spot Cavity spots occur on roots while in the ground.  They are caused by a calcium deficiency in the soil, and can be prevented by maintaining adequate Ca and moisture levels in the soil.

HARVESTING
    Carrots are ready to harvest 50 to 85 days after planting.  They are machine harvested by mowing the tops then lifting the roots with a modified sweet potato harvester, or by loosening the soil with a specialized plow (carrot lifter) which harvests the crop in one pass.
    Carrots destined for processing are similarly harvested; however, they differ in maturity.  After harvesting, they are washed and sorted, and loaded into palletized boxes or packaged for bulk storage.
    For fresh market, carrots with tops intact are harvested by hand.  They are bundled together with generally twelve to a bunch and sent to a packaging house to be quickly washed and hydrocooled. Next, they are placed in waterproof cartons, topped with ice, and shipped. Because of the high respiration, the temperature of carrots during the harvest and storage period must be closely monitored and kept low.
    Various “baby” carrots are created by peeling, cutting, and grinding of the Imperator or the Chantenay types.
    California, Texas, and Florida lead in US production of carrots.  In 1996, there were 123,060 acres of carrots in cultivation in the US and had a value of $400 million. In 1986, a farmer could expect a yield of 287 cwt. per acre.  Carrots are harvested for market eery month of the year in the United States.

Carrot harvester

Carrot harvester

For maximum quality, carrots in storage should be held just above 32°F and 98% relative humidity.  Topped carrots can be stored at these conditions for 4-5 months without noticeable quality loss.  Bunched carrots lose quality quickly, and should be sold shortly after harvest.     Modern storage technology has made it possible to store quality carrots for 6-9 months.   Controlled atmosphere storage at 3% O2 and 6% CO2 greatly increases the length carrots can be stored.     Quality factors for carrots include the sugar content (which tends to increase in storage), internal and external color, and crispness. Limp or woody carrots are unmarketable.     Carrots are most often packaged in plastic bags colored orange to enhance the carrot appearance.

Packaged carrots