Tomatoes (Lycopersicon esculentum) can be grown on
almost any moderately well-drained soil type. A good supply of organic
matter can increase yield and reduce production problems. Tomatoes and
related vegetables, such as potatoes, peppers and eggplants, should not be
planted on the same land more than once in three years. Ideally, any cover
crop or crop preceding tomatoes should be members of the grass family. Corn,
an excellent rotation crop with tomatoes, supplies large amounts of organic
matter and does not promote the growth of disease organisms that attack
tomatoes. Certified seeds and plants are recommended and should be used
Bacterial wilt or Southern bacterial blight is a serious
disease caused by Ralstonia solanacearum (formerly Pseudomonas
solanacearum). This bacterium survives in the soil for extended periods
and enters the roots through wounds made by transplanting, cultivation or
insects and through natural wounds where secondary roots emerge. Disease
development is favored by high temperatures and high moisture. The bacteria
multiply rapidly inside the water-conducting tissue of the plant, filling it
with slime. This results in a rapid wilt of the plant, while the leaves stay
green. If an infected stem is cut crosswise, it will look brown and tiny
drops of yellowish ooze may be visible.
Prevention and Treatment: Control of bacterial wilt of
plants grown in infested soil is difficult. Rotation with nonsusceptible
plants, such as corn, beans and cabbage, for at least three years provides
some control. Do not use pepper, eggplant, potato, sunflower or cosmos in
this rotation. Remove and destroy all infected plant material. Plant only
certified disease-free plants. The varieties Neptune and Tropic Bay are
partially resistant to bacterial wilt, but are uncommon varieties. Chemical
control is not available against this disease.
This disease is caused by the fungus Alternaria
solani and is first observed on the plants as small, black lesions
mostly on the older foliage. Spots enlarge and concentric rings in a bull’s
eye pattern can be seen in the center of the diseased area. Tissue
surrounding the spots may turn yellow. If high temperature and humidity
occur at this time, much of the foliage is killed. Lesions on the stems are
similar to those on leaves, sometimes girdling the plant if they occur near
the soil line (collar rot). On the fruits, lesions attain considerable size,
usually involving nearly the entire fruit. Concentric rings are also present
on the fruit. Infected fruit frequently drops.
The fungus survives on infected debris in the soil, on seed,
on volunteer tomato plants and other solanaceous hosts, such as Irish
potato, eggplant, and black nightshade.
Prevention and Treatment: Use resistant or tolerant
cultivars. Use pathogen-free seed and do not set diseased plants in the
field. Use crop rotations, eradicate weeds and volunteer tomato plants,
fertilize properly, and keep the plants growing vigorously.
If disease is severe enough to warrant chemical control,
select one of the following fungicides: maneb, mancozeb, chlorothalonil, or
fixed copper. Follow the directions on the label.
Late blight is a potentially serious disease of potato and
tomato, caused by the fungus Phytophthora infestans. Late blight is
especially damaging during cool, wet weather. The fungus can affect all
plant parts. Young leaf lesions are small and appear as dark, water-soaked
spots. These leaf spots will quickly enlarge and a white mold will appear at
the margins of the affected area on the lower surface of leaves. Complete
defoliation (browning and shriveling of leaves and stems) can occur within
14 days from the first symptoms. Infected tomato fruits develop shiny, dark
or olive-colored lesions, which may cover large areas. Fungal spores are
spread between plants and gardens by rain and wind. A combination of daytime
temperatures in the upper 70s ° F with high
humidity is ideal for infection.
Prevention and Treatment: The following guidelines
should be followed to minimize late blight problems:
- Keep foliage dry: Locate your garden where it will receive morning
- Allow extra room between the plants, and avoid overhead watering,
especially late in the day.
- Purchase certified disease-free seeds and plants. There are no late
blight-resistant tomato cultivars.
- Destroy volunteer tomato and potato plants and nightshade family
weeds, which may harbor the fungus.
- Do not compost rotten, store-bought potatoes.
- Pull out and destroy diseased plants.
- If disease is severe enough to warrant chemical control, select one of
the following fungicides: chlorothalonil, fixed copper, maneb or mancozeb.
Follow the directions on the label.
SEPTORIA LEAF SPOT
This destructive disease of tomato foliage (fruit is rarely
infected) is caused by the fungus Septoria lycopersici.
Infection usually occurs on the lower leaves near the ground, after plants
begin to set fruit. Numerous small, water-soaked spots with dark borders
surrounding a light gray center appear on the older leaves. Black specks,
which are spore-producing bodies, can be seen in the center of the spots.
Severely spotted leaves turn yellow, die and fall off the plant. The fungus
is most active when temperatures range from 60 to 80°
F and humidity is high. Defoliation weakens the plant, reduces the size and
quality of the fruit, and exposes the fruit to sunscald (see below). The
fungus can overwinter on crop residue from previous crops, decaying
vegetation and some wild hosts related to tomato.
Prevention and Treatment: Currently grown tomato
cultivars are susceptible to Septoria leaf spot. Crop rotation and
sanitation will reduce the amount of inoculum. Repeated fungicide
applications (see late blight) will keep the disease in check.
The fungus Cladosporium fulvum causes leaf mold. It
is first observed on older leaves near the soil where air movement is poor
and humidity is high. The initial symptoms are pale green or yellowish spots
on the upper leaf surface, which enlarge and turn a distinctive yellow.
Under humid conditions the spots on the lower leaf surfaces become covered
with a gray, velvety growth of the spores produced by the fungus. When
infection is severe, the spots coalesce, and the foliage is killed.
Occasionally, the fungus attacks stems, blossoms and fruits. Green and
mature fruit can have a black, leathery rot on the stem end.
The fungus survives on crop residue and in the soil. Spores
are spread by rain, wind or tools. Seeds can be contaminated. The fungus is
dependent on high relative humidity and high temperature for disease
Prevention and Treatment: Crop residue should be removed
from the field. Staking and pruning to increase air circulation helps to
control the disease. Avoid wetting leaves when watering. Rotate with
vegetables other than tomatoes. Using a preventative
fungicide program, the same as used for early blight control, can control
This disease is caused by the bacterium Xanthomonas
vesicatoria, which attacks green but not red tomatoes. Peppers are
also attacked. The disease is more prevalent during wet seasons. Damage to
the plants includes leaf and fruit spots, which result in reduced yields,
defoliation and sun- scalded fruit. The symptoms consist of numerous small,
angular to irregular, water-soaked spots on the leaves and slightly raised
to scabby spots on the fruits. The leaf spots may have a yellow halo. The
centers dry out and frequently tear.
The bacteria survive the winter on volunteer tomato plants
and on infected plant debris. Moist weather and splattering rains are
conducive to disease development. Most outbreaks of the disease can be
traced back to heavy rainstorms that occurred in the area. Infection of
leaves occurs through natural openings. Infection of fruits must occur
through insect punctures or other mechanical injury.
Bacterial spot is difficult to control once it appears in
the field. Any water movement from one leaf or plant to another, such as
splashing rain drops, overhead irrigation, and touching or handling wet
plants, may spread the bacteria from diseased to healthy plants.
Prevention and Treatment: Only use certified
disease-free seed and plants. Avoid areas that were planted with peppers or
tomatoes during the previous year. Avoid overhead watering by using drip or
furrow irrigation. Remove all diseased plant material. Prune plants to
promote air circulation. Spraying with fixed copper will control the
disease. Follow the instructions on the label.
Buckeye rot is a disease of the fruit caused by the fungus
Phytophthora parasitica. The first fruit symptoms appear as
brownish spots, often at the point of contact between the fruit and the
soil. As the spots enlarge, dark, concentric rings can be seen. Lesions of
buckeye rot resemble those of late blight, except that the former remain
firm and smooth, whereas late blight lesions become rough and are slightly
sunken at the margins. Under moist conditions, a white, cottony fungal
growth appears on the buckeye rot lesions. With time, the entire fruit will
rot. The fungus does not affect the foliage. The disease is most common
during periods of prolonged warm, wet weather and in poorly drained soils.
The fungus survives in the soil and is spread by surface water and rain.
Peppers are also susceptible to this disease.
Prevention and Treatment: Avoid compacted, poorly
drained soils (grow plants in raised beds). Rotation, sanitation, staking
and mulching will help reduce the disease. Fungicides applied for late
blight control will also control buckeye rot.
This is a warm-weather disease caused by the fungus
Fusarium oxysporum. The first indication of disease in small
plants is a drooping and wilting of lower leaves with a loss of green color
followed by wilting and death of the plant. Often leaves on only one side of
the stem turn golden yellow at first. The stem of wilted plants shows no
soft decay, but when cut lengthwise, the woody part shows a dark brown
discoloration of the water-conducting vessels. The fungus is soilborne and
passes upward from the roots into the water-conducting system of the stem.
Blocking of the water-conducting vessels is the main reason for wilting.
Invasion occurs through wounds in roots growing through infested soil.
Long-distance spread is through seed and transplants.
Prevention and Treatment: Control can be obtained by
growing plants in pathogen-free soil, using disease-free transplants and
growing only varieties resistant to races 1 and 2 of Fusarium wilt
(indicated by FF following the tomato variety name), such as: Celebrity,
Solar Set, Park’s Whopper, Goliath, Dona, Big Beef, Health Kick, Viva
Italia, and Classica. Raising the soil pH to 6.5-7.0 and using nitrate
nitrogen rather than ammoniacal nitrogen will retard disease development. No
chemical control is available.
The fungus Sclerotium rolfsii causes this disease.
The first symptom is drooping of leaves suggestive of other wilts. On the
stems, a brown, dry rot develops near the soil line. White fungal growth
with brown, mustard-seed-sized sclerotia (hardened fungal structures used to
survive unfavorable growth conditions) may be visible. The stem lesion
develops rapidly, girdling the stem and resulting in a sudden and permanent
wilt of all aboveground parts. Frequently, a white fungal mat covers the
lesions. The fungus can also attack fruits where they touch the soil.
The fungus can survive for years in soil and plant debris.
It is favored by moist conditions and high temperatures.
Prevention and Treatment: Crop rotation with
nonsusceptible grass crops and removal of plant debris immediately after
harvest will help to control the disease. Do not plant tomatoes after beans,
pepper or eggplant. Calcium nitrate may be applied at transplanting.
SEEDLING DISEASE (DAMPING-OFF)
The fungi Pythium and Rhizoctonia cause
damping-off of tomato seedlings. Seedlings fail to emerge in the greenhouse
or small seedlings wilt and die soon after emergence or transplanting.
Surviving plants have watersoaked areas on the stem close to the soil line.
Prevention and Treatment: Damping-off is often a
problem in plants that are planted too early in the spring. The fungi are
more active in cool, wet, rich soils. To prevent damping-off, take these
- Start seeds indoors in sterilized potting mix.
- Do not start seeds in soil that has a high nitrogen level. Add
Nitrogen fertilizer after the seedlings have produced their first true
- Allow the surface of the soil to dry between waterings.
Different viruses cause different symptoms on tomato.
Symptoms of virus infection may appear as light and dark green mottling of
the leaves. With tomato spotted wilt virus (TSWV), plants are stunted,
bronzed or spotted, or have prominent purple veins. Fruits may have yellow
spots. Tobacco mosaic virus (TMV) causes mottling of older leaves and may
cause malformation of leaflets, which may become shoestring-like in shape.
Viruses are highly infectious and readily transmitted by any means that
introduces even a minute amount of sap from infected into healthy plants.
Prevention and Treatment: There are no chemical
controls for viruses. Destroy infected plants promptly. Wash hands
thoroughly after smoking (the tobacco mosaic virus may be present in certain
types of tobacco) and before working in the garden. Eliminate perennial
weeds near the garden. Control insects (thrips and whiteflies) that carry
viruses. Rotate tomatoes with crucifers (such as cabbage, broccoli and
turnips). Plant TSWV resistant varieties, such as BHN 444 Hybrid and Health
Kick. Many varieties have TMV resistance, such as: Bush Celebrity, Bush
Early Girl, Jetsetter, Big Beef, Dona, Celebrity, Keepsake, Sweet Cluster,
Sweet Million (cherry), and Super Marzano (paste).
Root-knot nematodes are microscopic worms that live in the
soil and in plant roots. Affected plants are usually stunted, discolored and
may die. Knots or galls develop on the roots.
Prevention and Treatment: When nematodes are not yet
present, move the garden location every year, purchase disease-free plants,
pull up roots immediately after harvest and use resistant varieties
(indicated by N following tomato variety): Better Boy, Celebrity, Sweet
Cluster, Keepsake, Big Beef, Dona, Small Fry, Sugar Snack, Classica, and
When root-knot nematodes are present, relocate the garden to
a nematode-free area. Use nematode resistant varieties. Establish a rotation
system with marigolds (varieties Tangerine, Petite Gold and Petite Harmony)
which reduce root-knot nematode populations in soils. Soil solarization can
also help reduce populations of nematodes in the garden.
Blossom End Rot: Blossom end rot is a physiological
disorder of tomato. Symptoms are water-soaked spots on the blossom end of
the fruit. These spots enlarge and become black. Secondary infection by
decay-causing organisms usually follows.
The cause of this disorder is a calcium deficiency in the
developing fruit. Extreme fluctuations in moisture, root pruning and
excessive nitrogen fertilization can also enhance blossom end rot.
Prevention and Treatment: Maintain a uniform
supply of moisture through irrigation and soil mulches. Soil should be limed
according to recommendations of a soil analysis report. Using gypsum (1-2
pounds per 100 square feet) as a supplement to liming on calcium-deficient
soils has proven beneficial. Lime and/or gypsum should be applied before
planting. After tomatoes are planted, spray the foliage with calcium
chloride or calcium nitrate when symptoms first appear. Follow the
instructions on the label. Removing fruit with symptoms is recommended.
Growth Cracks: Tomatoes crack when
environmental conditions (drought followed by heavy rain or watering)
encourage rapid growth during ripening. Some cracks may be deep, allowing
decay organisms to enter the fruit and cause fruit rot.
Prevention: Maintain even soil
moisture with regular watering. Some varieties are crack-tolerant, such as:
Early Girl, Roma, Heinz 1439, First Lady, Ball’s Beefsteak and Rutgers.
Sunscald: Sunscald occurs when
tomatoes are exposed to the direct rays of the sun during hot weather. It is
most common on green fruit. Decay causing fungi frequently invade the
Prevention: Cover exposed
fruits. Control leaf diseases.
Poor Fruit Set: Poor fruit set
occurs for several reasons:
- Extreme temperatures: The blossoms drop off without setting fruit when
temperatures are below 55° F or above 90°
F for extended periods. Try Sunmaster Hybrid for heat-tolerance.
- Dry soil: Blossoms dry and fall when the plants do not receive enough
- Shading: Few blossoms are produced when the plants receive less than
six hours of sun a day.
- Excessive nitrogen: high nitrogen levels in the soil promote leaf
growth at the expense of blossom and fruit formation. Correct the nitrogen
imbalance with superphosphate or 0-10-10 fertilizer.
Catfacing: This is a disorder
caused by cold temperatures during fruit set. The fruit is extremely
malformed and scarred, usually at the blossom end. Fruits that develop later
in the season will not be affected.
Prepared by Marjan Kluepfel, HGIC Information
Specialist, James H. Blake and Anthony P. Keinath, Extension Plant
Pathologists, Clemson University. Revised by Joey Williamson, HGIC