Celery, Celeriac (Apium)
Plant Health Problems
Diseases caused by Fungi:
Fusarium yellows, Fusarium oxysporum f. sp. apii.
The disease first appears in the field as stunted, yellow, and
wilting plants. If the plant crown and roots are sliced open with
a knife, the water-conducting tubes in the plant will be
discolored. The disease can lead to plant death if susceptible
cultivars are grown. The fungus is soilborne and can persist in
soil for long periods of time. The fungus can survive on weeds
and other crop plants without exhibiting symptoms.
Two- to three-year rotation with cucurbits and onions will reduce
soil inoculum. Moderately resistant plants are also available.
Root and crown rot, Rhizoctonia solani, Pythium
spp.
Symptoms appear as wilting and a slow or rapid collapse of the
plant. The roots can appear brown and water-soaked instead of
white. A water-soaked lesion can often appear at the base of the
stem.
Control can be achieved by improving water drainage in the field
and using a two-year rotation with nonsusceptible plants, such as
corn, to prevent the buildup of pathogenic organisms.
Early blight, Cercospora apii.
This blight is caused by a fungus and appears as large,
irregular, dark-brown spots on the leaves and stems. The leaf
spots are generally bounded by the veins. In severe cases, the
spots grow together and kill the leaves. Early blight is caused
by a fungus which may be carried in the soil or on the seed. The
fungus does not live in the seed for more than two years.
When using newer seed, it may be best to disinfect it by dipping
for 30 minutes in hot water (118 F). The incidence of this
disease in Connecticut is rare. Control can also be achieved with
the use of fungicide sprays applied as soon as symptoms are
visible. Among the compounds registered for use in Connecticut
are chlorothalonil, thiophanate-methyl, or copper
sprays. Consult the label for dosage rates and safety
precautions.
Late blight, Septoria apii.
Late blight is a common fungus disease of celery in Connecticut
which appears as small, circular, tan leaf and stem spots.
Usually there are small, black dots scattered across the tan
spots. Gelatinous threads of spores are exuded from these dots
during wet weather.
The disease is not a major problem in Connecticut and usually
does not require controls. However, control can be achieved with
the use of fungicide sprays applied as soon as symptoms are
visible. Among the compounds registered for use in Connecticut
are chlorothalonil, maneb, thiophanate-methyl, or copper
sprays. Consult the label for dosage rates and safety
precautions.
Diseases caused by Phytoplasmas:
Aster yellows, phytoplasma.
Celery that has aster yellows has an abnormal number of leaves.
The leaves are yellow, twisted, and stunted. The roots remain
slender and have an abnormal number of fine hairy roots. Aster
yellows of celery is caused by a bacterium-like organism called a
phytoplasma which also causes the disease on asters, carrots, and
lettuce. The phytoplasma is carried by leaf hoppers.
To keep down the amount of disease, growers should control
leafhoppers with insecticides and avoid planting carrots near
asters.
Diseases caused by Nematodes:
Pin nematodes, Pratylenchus hamatus.
The pin nematodes are too small to see with the naked eye, but
they live in the soil and feed on the roots of celery and other
plants. They stick their stylets into the plant roots and suck
the food from the plant tissue. Although the nematodes are
individually very small, they may be present in such numbers that
they will cause stunting and yellowing of celery and other crops.
Rotation with nonsusceptible plants, such as corn, can reduce the
number of pin nematodes in the soil. Growing celery in a new area
will also control the disease. Care should be taken to avoid
carrying any soil from the old site to the new site.
Root-knot nematodes, Meloidogyne hapla.
Infected plants are stunted and sickly, with knots on their
small, feeding roots. This disease is caused by nematodes which
can persist in the soil for years.
Rotation with nonsusceptible plants, such as corn, can reduce the
number of nematodes in the soil. Growing celery in a new area
will also control the disease. Care should be taken to avoid
carrying any soil from the old site to the new site.
Diseases caused by Physiological/Environmental Factors:
Boron deficiency or cracked stem.
Celery deficient in boron has many parallel cracks across
their stems. Later the tissue between the cracks curls up in
strips. The leaves of deficient plants may show areas of brownish
discoloration.
Applying a balanced fertilizer that is supplemented with
micronutrients can reduce the incidence of cracked stem.
Heart rot, calcium deficiency.
Celery plants grown in hot weather can frequently develop a
calcium deficiency in the center of the crown causing it to not
develop. Soft-rotting bacteria frequently enter and cause a wet
slimy rot.
Control is difficult to achieve, but efforts to water the plant
more regularly and use mulching can reduce the incidence of heart
rot.
Insect Problems:
Most insects on celery also feed on carrot. See
Carrot for information on additional insects.
Celery leaftier, Udea rubigalis.
Although this small greenish-white striped caterpillar may
occasionally feed on leaves, it is not a serious pest and control
is rarely needed.
Parsnip webworm, Depressaria pastinacella.
When parsnip and celery are grown for seed, some injury may be
caused by this caterpillar which webs together and feeds upon the
unfolding blossom heads. The caterpillar is slightly more than
1/2" long when full grown, greenish yellow with black head
and legs, and covered with small black warts. There is one
generation a year and the moths live through the winter. When
nearly mature, the caterpillars leave the web and burrow inside
the flower stems where they pupate. Control is not usually
necessary.
Tarnished plant bug,
Lygus lineolaris.
This bug injures many different kinds of plants by sucking sap
from the tender leaves and shoots. On celery the injury shows as
darkened sunken areas about 1/4" in diameter on the leaves
and shoots near the top of the plants. Feeding in the heart can
also cause the death of young leaves, which may then be degraded
by soft rot. The tarnished plant bug is a mottled brownish bug
about 1/5" long that hibernates in protected places. The
eggs are inserted in the tender tissues of plant stems, leaves,
and buds, and the young bugs or nymphs are yellowish green and
pass through five nympal stages before becoming adult. The adults
are good fliers, and often move into vegetable crops from feeding
on hayfields or weeds. Nymphs are not usually found on celery. A
recently introduced parasitoid of the tarnished plant bug, Peristenus
digoneutis, attacks the nymphs of the tarnished plant bug on
alfalfa and may help to reduce populations moving into vegetable
crops. Carbaryl is registered for control of this pest in
Connecticut, but observe the long interval required between
insecticide treatment and celery harvest. Also consult the label
for dosage rates and safety precautions.
Twospotted spider mite, Tetranychus urticae.
This mite, which is about 1/16" long when mature, lives on
the underside of leaves where it sucks plant sap. The leaves of
infested plants have a sickly appearance, with yellow or
reddish-brown blotches. Webbing may be visible in heavy
infestations. Injury is most severe in hot, dry weather. Natural
enemies normally regulate the population as long as pesticide use
is avoided, so control is not usually necessary.