Carrot Production in
California
Carrot Country
Summer 2006
By Milt McGriffen, Joe Nunez, Trevor Suslow and Keith Mayberry
Production Areas and Season
California has four main production areas for carrots : the southern San Joaquin
Valley and the Cuyama Valley (Kern and Santa Barbara counties); the southern
desert (Imperial and Riverside counties); the high desert (Los Angeles County);
and the central coast (Monterey County).
Carrots are grown year-round in California. In the southern San Joaquin and
Cuyama Valleys, carrots are planted from December to March for harvest from
May to July and from July to September for harvest from November to February.
In the southern desert, they are planted from August to February for harvest
from December to June. In the high desert they are planted from April to July
for harvest from August to December. On the central coast, they are planted
from December to August for harvest from April to January.
Fresh Market Carrot Acreage and Value
Year Acreage Average yield Gross value/acre
(tons/acre)
1995 63,500 14.50 $4,379
1994 58,300 16.25 $3,741
1993 1,200 15.00 $3,339
Source: California Agriculture Statistics 1995 (Sacramento: California Department
of Food and Agriculture. 1996).
Processing Carrot Acreage and Value
Year Acreage Average yield Gross value/acre
(tons/acre)
1995 5,100 23.90 $1,765
1994 4,100 39.90 $2,350
1993 6,800 14.70 $1,425
Source: California Agricultural Statistics 1995 (Sacramento: California Department
of Food and Agriculture. 1996).
Climate Requirements
Carrots, a cool-season crop, will tolerate warm temperatures early in the growing
season. Roots attain optimal color when the air temperature is 60 to 70ºF
(18 to 21ºC). Root color can deepen rapidly when temperatures are within
this range three weeks before harvest. Above 86ºF (30ºC), the growth
of foliage is reduced and strong flavors develop in the roots, reducing their
market quality. Below 50ºF (10ºC), carrot roots and foliage grow
slowly. Carrots may tolerate some frost.
Varieties and Planting Techniques
Consumer demand for uniform roots of deep orange color has led to extensive
use of Imperator type hybrids. Varieties include Sugarsnaxs, Topcut, Primcut,
Trinity, Tastypeel, Apache, Navajo and Choctaw. Long Imperator 58 is the
standard open-pollinated variety. Nantes-type varieties, commonly grown in
Europe and in home gardens, are not normally grown commercially in California.
Carrots are always direct seeded. Both natural and pelleted seed are used.
Carrot seed vary from 175,000 to 400,000 per pound and are sown at the rate
of 0.9 to 1.3 million seeds/acre. Higher densities are used for plantings for
the cut-peel market. Seed within a lot vary significantly in size, maturity,
vigor and germination time; emergence often occurs over several days. Seed
are most commonly sown in six or eight lines in beds 40 inches wide with three
or four rows on each bed shoulder. Seed are placed in a narrow groove and are
lightly covered.
Soils and Irrigation
The upper 30 inches (75 cm) of soil should be uniform and free of barriers
to root growth. Although carrots are often grown on sandy soils, the ideal
soil is silt loam which provides the best combination of water-holding capacity
and drainage. Heavy soils can result in hairy, deformed roots. A favorable
pH for carrots is between 5.5 and 7.0.
A uniform water supply is critical for good color and root formation. If significant
wet-dry cycles occur, the roots will split. Excessive watering discourages
good color formation and may encourage disease. Carrots are usually irrigated
by solid-set sprinklers. In the Imperial Valley, the carrots are germinated
by solid-set sprinklers then switched to furrow irrigation at the first cultivation.
Drip irrigation has been tested with carrots, but the results have been poor.
Fertilization
If the field has some residual nitrogen (N) from a previous crop, no N need
be applied before seedlings emerge. Carrot roots may fork if too much N is
applied preplant. Sidedressing 60 to 80 lb/acre (67.2-89.6 kg/ha) of N is
typical during the growing season. Nitrogen-deficient carrots often have
leaves with an apparently healthy green appearance, but the height of tops
throughout the field may be irregular. Phosphorous (P) is applied as 0-45-0
(treble superphosphate) at 400 to 500 lb/acre (448-560 kg/ha) before listing.
Petiole sampling is recommended for carrots. Researchers have determined the
adequate nutrient concentrations that should be present in a dried sample of
the most recently mature leaf. Nutrient levels above or below the following
ranges can lead to unmarketable roots. The following table shows ranges of
nutrients in carrot petiole samples from an adequately fertilized crop:
Percentage of total tissue
N P K Ca Mg
1.8-2.5 0.2-0.4 2.0-4.0 2.0-3.5 0.2-0.5
Parts per million
Fc Mn Zn B Cu
30-60 30-60 20-60 20-40 4-10
Root Forking, Stubbing and Color
Damage to the growing root tip may cause the carrot root to fork or stub, rendering
it unmarketable. Forking or stubbing often occurs within a few weeks after
the seed germinate. Many diseases can cause forking. Poor soil structure,
improper irrigation management or hard freezes can also cause forking or
stubbing. To help prevent forking and stubbing, prepare the soil well so
that it has good tilth and drainage and avoid over- or under-watering young
carrots.
As the carrot root matures, carotene accumulates, causing the root to change
from yellow-white to yellow and then orange. Although varieties differ in their
potential for orange color, soil fertility, temperature and water content have
the main effects on root color. The health of the leaves plays a minor role
in root color unless the tops are severely stressed.
Integrated Pest Management
Integrated pest management (IPM) information is continually being developed
for carrots. Cultural control methods such as mechanical cultivation, field
sanitation, good drainage and irrigation management are important components
of IPM that help minimize chemical controls. Herbicides, insecticides, nematicides
and fungicides should always be used in compliance with label instructions.
Contact the UC IPM World Wide Web site at http://www.ipm.udcdavis.edu for
current pest management information: (see UC IPM Pest Management Guidelines,
DANR Communication Services Publication 3339).
Weed management. Many weeds, including summer and winter annuals and perennials,
are pests of carrots. Nutsedges, both yellow and purple, are the worst weed
pests in carrots. Postemergence herbicides control yellow nutsedge, but no
herbicide is registered for purple nutsedge control in carrots. Cultivation
and preplant chemical treatments offer some control of nutsedges, and fallow
summer treatments can also be effective. Nutsedges do not compete with fall-planted
carrots because nutsedge growth slows and eventually ceases as temperatures
cool and as carrots provide more shade. Pre- or postemergence herbicides are
available for control of grass, cereal and broadleaved weeds; chemicals applied
to control nematodes may also control weeds. Consult your local pest control
farm advisor for details.
Insect identification and control. Crickets, grasshoppers, pale-striped flea
beetle larvae and adults, cutworms and saltmarsh caterpillars can be serious
pests of carrots by feeding on seedlings. Remove weeds in or near fields and
disk in plant residue from infested fields to help keep flea beetle populations
low.
Saltmarsh caterpillars are a problem in carrot fields planted next to a cotton
field that has been defoliated for harvest. Building trenches or other barriers
at the border of the cotton field can stop the movement of these pests.
Aphids and whiteflies can be serious pests of carrots at all stages of development.
Besides directly feeding on carrots, they also vector several viral diseases.
Chemical control is usually not required for aphids because naturally occurring
predators and parasites help keep their populations below economic threshold
levels. Field sanitation helps reduce the aphid population. Carrots should
not be planted near cotton or melons to reduce the movement of the cotton-melon
aphid into carrot fields when these crops are harvested.
Disease identification and management. Pythium ultimum, P. irregulare, Rhizoctonia
solani and Macrophomina spp. Can all cause forking, stubbing and dieback. Soil
fumigation can reduce the amount of dieback in a field and control several
other pests as well. Powdery mildew, a fungal disease, can be a problem in
high humidity and warm temperatures. Symptoms of powdery mildew are white powdery
growths on the upper surface of the leaves. Seedling damping-off can be the
result of Pythium spp.,
R. solani and other soilborne fungal pathogens. Seed treatments and soil fumigation
to control nematodes and/or weeds can reduce damping-off pathogens.
Cavity spot can be a severe disease of carrots that can cause the loss of the
entire crop. Small, brown, water-soaked lesions develop on the root surface
and may enlarge and open into a dry sunken lesion as the carrot matures. This
disease is caused by the soilborne pathogen Pythium violae. Cavity spot generally
increases in fields with a previous history of carrot plantings. Alfalfa is
also a host for P. violae, and carrots that follow alfalfa may show symptoms.
Fungicide applied preplant and in two to three postplant applications reduces
cavity spot.
Root rots of carrots can be caused bys several plant pathogens. Cottony soft
rot (Sclerotinia sclerotiorum), a problem in cool, moist conditions, is a cottony
white mass of fungal growth around the base of the carrot. Large black sclerotia
can be found in the fungal mass and on the carrot itself. It can be reduced
by deep plowing before planting and by chemical treatments.
Southern blight (Sclerotium rolfsii) favors warm temperatures. It produces
a low-lying dense mat of brown fungal growth on the soil surrounding the carrot,
with brown sclerotia located throughout the fungal mat. It can be reduced by
deep plowing before planting and rotating to nonhost crops such as small grains
or corn.
Bacterial soft rot (Erwinia carotovora) can be recognized as a soft rot not
associated with any fungal growth and accompanied by a foul odor. It occurs
in waterlogged soils during warm temperatures. Preparing the soil to eliminate
low spots, increasing drainage and avoiding overwatering are control measures
for all the soft rots.
Leaf blights are caused by several pathogens and can be difficult to identify
in the field. Alternaria leaf blight (Alternaria dauci) can be very serious.
Symptoms appear as dark-brown to black necrotic lesions along the margins of
the leaves and on the petioles. Symptoms first appear on the older foliage
and then on younger leaves if warm, moist conditions persist. Long-beaked,
multi-celled comidia can be seen with the aid of a microscope on the leaves
and petioles of diseased plants. Under a microscope, carrot early blight (Cerocospora
carotae) can be differentiated from alternaria leaf blight by the very thin
threadlike spores. C. carotae produces on the lesions.
Bacterial blight (Xanthomonas campestris) symptoms are slightly different from
those of alternaria leaf blight in that the lesions are not as dark and may
be surrounded by a yellow halo. Bacterial oozing may also be seen on the lesions
present on the leaves and petioles. The bacterial exudates are particularly
visible on the flower stalks of plants that have bolted. Alternaria leaf blight
and bacterial blight are seedborne diseases that can be avoided by planting
seed known to be disease free. Fungicides can be used for control of early
blight and alternaria blight. Copper fungicides work best for bacterial blight,
although this disease is rarely a serious problem.
The main symptoms of black root rot (Alternaria radicina) are black lesions
on the base of the petioles. The lesions may extend down into the root, causing
the characteristic “black crown.” Crop rotation may reduce the
spores in the soil; the spores are known to survive in the soil for more than
five years without a host. Plowing, to turn the spores under, has been shown
to reduce the incidence of this disease in fields with a history of black root
rot. Fungicides can also be used for control but need to be directed at the
canopy to protect the petioles and crown.
Two viruses affect carrots in California. Carrot motley dwarf is found in the
cooler carrot-growing regions along the central coast. Infected plants appear
stunted and have reddish tops. The disease is transmitted by aphids to newly
planted fields from previously infected overwintering fields and can be controlled
by avoiding planting near overwintering carrot fields. Carrot thin leaf is
another aphid-vectored viral disease that can spread from infected volunteer
carrots. Symptoms are the thin leaves that give the virus its name. Eliminating
volunteer carrots reduces the chances of the virus spreading into newly planted
fields.
Nematodes. The root-knot nematode (Meloidogyne spp.), the primary nematode
pest of carrots, causes stubbing, forking and galling. It is found in all carrot-growing
regions of California. Other nematode pests include the stubby root nematode
(Trichodorus spp. and Paratrichodorus spp.) and the needle nematode (Longidorus
africanus). Nematicides or soil fumigants are used to control nematodes. Soil
fumigants applied by chemigation or injection into the soil may give other
benefits such as weed and soilborne disease control. Crop rotation can also
reduce these pests.
Harvesting and Handling
Commercially grown carrots are harvested using self-propelled multi-row harvesters.
Some machines can harvest more than 1,000 tons (907 t) of carrots per day
(about 30 semi-truck loads). The 4-row machines dig two beds 42 inches (105
cm) wide per pass, lift the roots using a system of belts, shear off the
tops and deposit the roots into a waiting truck or trailer. The carrots are
then hauled to a shed for washing, grading, sizing and packing. In the Central
Valley, carrots are hauled a short distance, usually to sheds in Bakersfield,
whereas carrots grown in the deserts may be hauled over 300 miles. The grower
pays part of the freight to the shed. On average, 40 to 80 percent of all
the carrots growing in the field are harvested and “packed out.” Carrots
that are damaged by the harvester or by insects or are diseased, deformed
or off-color are culled.
Carrots may be grown specifically for the cut-peeled carrot market, or culled
carrots may be cut and peeled to the desired size. Harvesting carrots for the
mini-carrot and cut-peeled market is difficult because of the high density
of roots. During harvesting, excess dirt may be picked up., increasing the
tare hauled to the shed. Dirt is also expensive to remove and dispose of at
the shed. For bunched carrots, a small acreage of which is planted in California,
the beds are undercut and the carrots are hand-sorted in the field. The green
tops are bound with a wire twist tie, and the bunches are loaded onto flatbed
trucks and hauled to the shed for washing and packaging. Careful handling of
carrots during and after harvest prevents bruising, shatter-cracks and tip
breaks and prolongs storage life.
Postharvest Handling
Before storage, carrots are generally washed and hydro cooled in clean water
with 100 ppm chlorine at pH 6.5 to 7.5 before being packed in plastic-lined
bins. Research has shown, however, that if carrots are to be stored for an
extended period, carrot quality is highest and postharvest losses lowest
if they are stored with the tops on unwashed and in plastic-lined bins. Topping
and handling during washing increases cracking and scuffing damage which
leads to increased rot. Unwashed storage has worked successfully with harvests
from light, sandy soils. Soil type, harvest conditions and local experience
should prevail in handling and storage decisions.
Ideal storage conditions for carrots are 32ºF (0ºF) at 99 percent
relative humidity (RH). Under these conditions, carrots have been stored successfully
for more than seven months with minimal losses (10 to 15 percent) due to dehydration
and decay. At 33.8ºF (1ºC) and 98 percent RH, the conditions common
in most storage, the maximum recommended storage is five months.
Carrots for the cut-peeled market are generally cut into 21-inch (5-cm) segments
(“slugs”). These carrots may be held in plastic-lined bins prior
to peeling and shaping and should have adequate air circulation and uniform
temperature during storage to minimize decay and sprouting. Bunched carrots
and forcing-type cut-peeled carrots are highly perishable, especially with
tops intact. They must be thoroughly precooled to 32ºF (0ºC) and
can be stored at this temperature at 99 percent RH for up to two weeks. Top
icing, although not necessary with properly precooled carrots, is often used
for bunched carrots to demonstrate that low temperature and high humidity existed
during transit.
During storage and transportation, carrots should not be exposed to ethylene
gas from propane-powered lift trucks or produce such as apples or pears. Ethylene
induces the production of compounds that cause bitterness in carrots.
Postharvest Disorders
The most important storage decays of carrots are gray mold (Botrytis spp.),
watery soft rot (Sclerotinia spp.), Rhizopus rot, bacterial soft rot (Erwinia
spp.), and sour rot (Geothrichurn spp.). Decay can be controlled by proper
storage and handling to prevent mechanical injury (fluctuations in temperature
during storage promotes water condensation and decay). Whiteness of the cut
or peeled surface (“white blush”), common on fresh-cut carrots
(cut-peeled, sticks or coins), is caused by dehydration. Use sharp cutting
blades and keep free moisture on work surfaces during packaging to prevent
this disorder. A white, edible coating that reduces white blush has been
developed that may be applied before packaging.
Shipping Containers
Shipping containers for the various types of processed carrots are as follows.
Topped: 50-lb carton/sack containing loose carrots or ten 5-lb film (cello)
bags; 40-lb carton of 1-lb cello bags; 26-lb carton of bunched carrots; 25-lb
carton of loose carrots; 24-lb carton of 1-lb cello bags; 15-lb carton of
twenty 12-oz cello bags. Bunched: 26-lb carton/crate. Mini-carrots: 20-lb
carton of 1-lb cello bags; 15-lb carton of twenty 12-oz cello bags. Fresh-cut:
18-lb carton of 1- or 2-lb cello bags; 9-lb carton of 1-lb cello bags.
Marketing
Carrots are shipped from California year-round. Shipments are highest from
December to August. California produces about 85 percent of all carrots grown
in the United States. Colorado, Florida, Michigan, Texas and Washington are
important carrot-producing states. Major carrot imports come from Canada
and Mexico.
Editor’s
note: The material here was recently updated by Joe Nunez,
plant pathology farm advisor, University of California Cooperative Extension,
Kern County. He can be contacted by phone at (661) 868-6200 or by e-mail at
jnunez@ucdavis.edu. The other authors are: Milt McGriffen, a vegetable specialist,
Department of Botany and Plant Sciences, UC, Riverside; Trevor Suslow, a postharvest
specialist, UC, Davis; and Keith Mayberry, a UC Cooperative Extension farm
advisor, Imperial County.
© 2006 Columbia Publishing