U UNIVERSITY of
2006 Florida Plant Disease Management Guide: Carrot
(Daucus carota) 1
R. N. Raid2
Specific Common Diseases
Alternaria Leaf Spot (Alternaria dauci)
Symptoms: The disease usually starts on the leaf
margins of older leaves, causing dark-brown to black
spots with yellow borders. The expansion of
numerous spots on a leaf will cause chlorosis
(yellowing) and eventually necrosis (death) of the
entire leaflet. Likewise, a few spots on the petioles
(stems) may result in the death of an entire leaf. This
fungal pathogen may also cause a shallow, firm, black
decay of the roots. Cool temperatures are most
favorable for disease development.
Cultural Controls: Host-plant resistance is
available for leaf spot, so resistant cultivars should be
planted whenever possible.
Chemical Controls: See PPP-6.
Bacterial Blight (Xanthomonas campestris
Symptoms: The disease appears as irregular
brown spots on leafs and dark brown streaks and
spots on petioles. Lesions begin as small yellow
spots with an irregular halo. Root infections appear
as brown to reddish spots, which may be either
sunken or raised, splitting open.
Seed Treatment: Use pathogen-free seed
whenever possible. If seed is known to be
contaminated, treat seed for 25 minutes in water at
1260F. Indexing of seed for this disease can be done
Chemical Control: See PPP-6.
Cavity Spot: (Pythium spp.)
Symptoms: The disease appears as lens-shaped
cavities on the roots with the longer axis of the cavity
oriented perpendicular to the length of the roots.
Spots may be up to 1/2 inch in length and are
generally less than 1/4 inch deep. Spots may or may
not have a dark color. Frequently, a depression may
occur and the lesion remains orange.
Cultural Controls: Where feasible, fallow
flooding is helpful in controlling this disease.
Resistant varieties and crop rotation are also effective.
In fields that are prone to standing water during the
1. This document is PDMG-V3-35, one of a series of the Plant Pathology Department, 2006 Florida Plant Disease Management Guide, Florida Cooperative
Extension Service, Institute of Food and Agricultural Sciences, University of Florida. This chapter was originally written by T. A. Kucharek, rewritten by
R. N. Raid. Rewrite published January 2006. Visit the EDIS Web Site at http://edis.ifas.ufl.edu.
2. R. Raid, professor, Plant Pathology Department, Everglades Research and Education Center--Belle Glade, FL; Florida Cooperative Extension Service,
Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611.
The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and
other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex,
sexual orientation, marital status, national origin, political opinions or affiliations. U.S. Department of Agriculture, Cooperative Extension Service,
University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry
2006 Florida Plant Disease Management Guide: Carrot (Daucus carota) 2
growing season, use raised beds. Early harvests also
allow for less disease.
Chemical Control: Use Ridomil at the time of
planting. See PPP-6. Seed treatments may also prove
Cercospora Leaf Spot (Cercospora carotae)
Symptoms: This fungal pathogen may affect all
foliar portions of the plant but not the root. Young
leaves are affected first, with the lesions starting
toward the margins. Spots are small and round and
frequently have a tannish-gray to black center with an
indefinite yellow halo. Numerous spots on the same
leaf may cause withering and death. Petiole lesions
are pale centered, elliptical, and tan. In contrast to
Alternaria leaf spot, Cercospora leaf spot is favored
by warm temperatures. Both are favored by extended
periods of leaf wetness.
Chemical Controls: See PPP-6.
Damping-Off (Rhizoctonia spp., Pythium
spp., Sclerotium rolfsii, Fusarium spp., and
Symptoms: Seedlings may damp-off at random
or in rapidly enlarging circular areas. In the
lattercase, lesions may be observed well up on the
petioles as well as at the soil line. Entire plantings
may be lost unless adequate control measures are
Cultural Controls: Plant carrots on raised beds
that are free of non-decomposed plant tissues from a
previous crop or weeds.
Chemical Controls: Use a fungicide seed
treatment. See PPP-6.
Pythium Brown Root (Pythium spp.)
Symptoms: Early infection results in a seedling
blight. Later infections result in the death of the root
tip, causing roots to branch excessively. Above
ground, infected plants will appear wilted and
stunted, and may exhibit a yellowing of the lower
leaves. Marketable yields may be drastically affected
by the production of rough, "hairy-root" tubers.
Cultural Controls: There is circumstantial
evidence that fallow flooding, similar to that
performed for Sclerotinia, may be helpful in
controlling this disease. Also, minimize damage to
raised beds with tractor tires and implements. Plant in
well-drained soil or fields not prone to flooding
during the growing season.
Rhizoctonia Cavity Spot (Rhizoctonia solani)
Symptoms: Early infection will cause seedling
damping-off On more mature plants, the disease
appears as a crown rot. Affected foliage will wilt and
die, leaving only a few viable inner leaves. Infected
crowns are dark brown to black, and infected roots
develop dry, sunken lesions where the lateral roots
Cultural Controls: While there is no totally
effective control, crop rotation may be of some
Sclerotinia Rot/White Mold (Sclerotinia
Symptoms: The fungal pathogen can cause a
damping-off disease but most frequently infects the
crown region where it may continue to develop after
harvest, causing a storage rot. The fungus infects the
base of the leaf stalk causing a brown tissue rot.
Individual leaves wilt and die. The disease is
characterized by the production of white cottony
mycelium which may spread from the crown into the
foliar tissues. Irregularly shaped, black fungal bodies
are soon formed and these are called sclerotia.
Infected roots may appear darker than normal at
harvest and these soon develop a soft, watery rot
either in the field or in storage. The disease may
spread rapidly in storage by root-to-root contact.
Cultural Controls: A number of activities will
assist in the control of white mold. All may be
needed for satisfactory control. These are:
1) Rotate to a non-susceptible crop like sweet
corn. Avoid rotating with susceptible crops like
lettuce or celery.
2) Turn soil at least 6 inches deep to bury the
sclerotia and old debris. These serve as inocula.
2006 Florida Plant Disease Management Guide: Carrot (Daucus carota) 3
3) Flood infested fields either continuously or
intermittently for 6 weeks during the summer where
Southern Blight (Sclerotium rolfsii)
Symptoms: Infection usually begins at or near
the soil surface. Rotting begins at the top of the
taproot and the base of the leaf petioles. Leaf tissues
turn brown and may wilt. A white mycelial growth
may appear on the soil surface. As the root rot
progresses downward, small spherical tan fungal
bodies called sclerotia may develop within the rotted
root tissues. Sclerotia of Sclerotium rolfsii are about
the size and shape of a cabbage seed and are usually
brown, differentiating this disease from white mold
caused by Sclerotinia sclerotiorum, which produces
larger, irregularly-shaped black sclerotia.
Cultural Controls: Use crop rotation with grass
crops and us a plow to aid in the burial of sclerotia
after planting a susceptible crop such as carrots,
pepper, tomato, beans, peanuts, etc.
Chemical Controls: See PPP-6. Strobilurin
fungicides may be effective for this disease although
it may not be officially listed on the label.