Southeastern U.S. Vegetable Crop Handbook - 2021 - 64

Begin by deep turning soils to bury any litter and debris and
breaking soils to a depth of 12-14 inches. Compacted soils or those
with tillage pans should be subsoiled to break the compacted areas.
If uncorrected, compact soil or tillage pans can result in restriction
of root expansion. It is best to apply lime after deep turning
to prevent turning up acid soil after lime application. Prepare a
good seedbed using bed-shaping equipment. Do not use disks or
rototiller to avoid soil compaction. Carrots should be planted on a
slightly raised bed (2-3 inches) to improve drainage. After beds are
tilled and prepared for seeding, it is best to allow the beds to settle
slightly before planting. Avoid other tillage practices that can increase
soil compaction. Following in the same tracks for all field
operations will help reduce compaction in planting areas.
SPECIAL NOTES FOR PEST MANAGEMENT
DISEASE MANAGEMENT
Root-Knot Nematode: By far, the most destructive problem in
carrots is root-knot nematodes. Root-knot nematodes are small eellike
worms that live in the soil and feed on plant roots. Since the
root of the carrot is the harvested portion of the plant, no root-knot
damage can be allowed. Root-knot causes poor growth and distorted
or deformed root systems which results in a non marketable
root. Root-knot damage also allows entry for other diseases such
as Fusarium, Pythium, and Erwinia.
If any root-knot nematodes are found in a soil assay, treatment
is recommended. Good success has been obtained using field
soil fumigation to eradicate root-knot nematodes in the root zone
of carrots. Use nematicides or fumigants listed in the " Nematode
Control in Vegetate Crops " tables in the Disease Control section.
SOIL-BORNE ROOT DISEASES
Depending on the cropping history of the field, Pythium, Southern
Blight, and Sclerotinia may cause problems. It is advisable
to avoid fields where these diseases have been identified in the
previous crop. Deep turning is also necessary to help prevent root
diseases.
Pythium Blight: is usually characterized by flagging of the foliage
indicating some root damage is occurring. Under wet conditions,
Pythium may cause serious problems to the root causing a white
mycelium mat to grow on the infected area which rapidly turns to a
watery soft rot. Forking of the root system is also a common symptom
associated with Pythium infection. Rotation is considered a
major factor in reducing Pythium along with the use of fungicides.
Southern Blight: Southern blight causes serious damage to carrots.
This disease is usually associated with carrots remaining in
the field after the soil begins to warm in the spring. This disease
causes a yellow top to develop with a cottony white fungal growth
associated with the upper part of the carrot root. The top of the root
and the surrounding soil may be covered with a white mycelium
with tan sclerotia developing as the disease progresses. Southern
Blight is best controlled by using rotation and deep turning.
Sclerotinia Blight: Sclerotinia blight causes serious damage to the
roots of carrots. This disease is usually worse under wet soil conditions.
White mycelium forms around the infected area and later,
64
dark sclerotia develop on the white mycelium which is a good indicator
of Sclerotinia rot. This disease causes a progressive watery
soft rot of the carrot root tissue and is considered a potential problem
in the production of carrots. Rotation and deep turning of the
soil are recommended to reduce losses to this disease.
Rhizoctonia: Rhizoctonia rot causes brown to black lesions to
develop on the sides of the carrot root. The disease is much worse
under cool, wet conditions. Saturated soil conditions often enhance
all soil-borne diseases which are potential problems in carrot production.
Rhizoctonia damage can be minimized by using rotation
and good cultural practices. Soil fumigation will prevent damage
with any of the soil inhabiting fungi.
FOLIAR DISEASES
Bacterial Blight: Bacterial blight causes irregular brown spots on
the leaves and dark brown streaks on the petioles and stems. The
lesions on the foliage begin as small yellow areas with the centers
becoming dry and brittle, with an irregular halo. The bacterium
affects the leaflets, stems and petioles as the disease progresses.
Some of these lesions may crack open and ooze the bacteria. These
bacteria may be washed down to the crown of the plant causing
brown lesions on the top of the root. The earlier the infection occurs
the greater the damage to the root. The bacterium is spread by
splashing water and takes about 10-12 days before symptoms appear
after inoculation. Disease development progresses rapidly between
77˚ and 86˚ F. Crop rotation is a major factor in controlling
Bacterial blight.
Alternaria Blight: Alternaria blight causes small dark brown to
black spots with yellow edges forming mostly on the leaf margins.
The spot increases as the disease progresses and in some cases entire
leaflets may be killed. In moist weather, the disease can move
so rapidly it resembles frost injury. Such conditions can reduce the
efficiency of mechanical harvesters which require strong healthy
tops to remove the carrot from the soil. Alternaria may also cause
damping off of seedlings and a black decay of roots. The spores
and mycelium are spread by splashing rains, contaminated soil,
or on cultivation tools. The disease can manifest itself in about 10
days after infection. The optimum temperature for Alternaria blight
is 82˚ F.
Cercospora Leaf Blight: Cercospora blight causes lesions to form
on the leaves, petioles and stems of the carrot plant. The symptoms
appear to mimic that of Alternaria blight but can be separated using
a compound microscope. Cercosproa blight progresses in warm,
wet weather and spots appear in about 10 days after infection. The
youngest leaves are usually more susceptible to Cercosproa infection.
INSECT
MANAGEMENT
Soil Insects: Wireworms, white grubs, and the granulate cutworm
may be partially controlled with good cultural practices. Soil
should be deep turned in sufficient time prior to planting to allow
destruction of previous crop residue that may harbor soil insects.
When possible, avoid planting just after crops that are slow to decompose
such as tobacco and corn. Avoid planting behind peanuts
and root crops such as sweetpotatoes and turnips. If a field has a
2021 Vegetable Crop Handbook for Southeastern United States
Southeastern U.S. Vegetable Crop Handbook - 2021

Table of Contents for the Digital Edition of Southeastern U.S. Vegetable Crop Handbook - 2021
