Common Tomato Problems
|This webpage will discuss the following insect and
disease issues: Aphids, flea beetles, colorado potato beetle,
hornworm, whitefly, root nematode, tobacco mosaic virus, walnut
wilt, verticillium wilt, fusarium wilt, alternaria, early blight,
late blight, bacterial wilt, growth cracks and blossom end
Leaves are sticky, yellow, and distorted
Aphids are tiny insects that come in many colors and suck plant
juices from the leaves. You’ll often find them in vast colonies on
succulent, new growth. Aphids excrete a sugary substance called
"honeydew," on which ants feed and on which black mold may develop.
Control: Spray with insecticidal soap, pyrethrins,
malathion, or diazinon.
Leaves have tiny, shotgun-like holes in them, about 1/8 inch in
Cause: Flea beetles.
Flea beetles are tiny black insects that hop like fleas when
disturbed. They chew little holes throughout the leaf surface.
Although flea beetles are rarely a problem to well-established
plants, you can spray them with pyrethrins, methoxychlor, diazinon,
Leaves have big, ragged holes in them, and some leaves even appear
to be missing.
Cause: Tomato hornworms
or Colorado potato beetles.
A tomato hornworm is a large, green worm with white diagonal
markings on its sides, and with a red or black curved "horn" at its
rear. Only a few may be present but they are absolutely voracious
eaters. You might come across a
that has what looks like grains of rice on its back; these rice
grains are actually the cocoons of the parasitic braconid wasp. When
the wasps pupate, they will feed on (and eventually kill) the
hornworm. The Colorado potato beetle is a yellow, black-striped
insect. Its larva is large and red, with two rows of black dots on
its sides. Both the adults and larvae can severely damage plants by
feeding on leaves and stems.
Control: For hornworms, here’s one of the few times when
hand-picking the pest is suitable for the weekend gardener. You can
also spray with the biological insecticide Bt (Bacillus
thuringiensis). And if you find one that is parasitized with the
wasp, don’t spray it. The wasps are beneficial insects that can
infest other hornworms after they mature. Bt will also kill the
Colorado potato beetle larvae. For the adult, though, you can spray
with pyrethrins, diazinon, methoxychlor, or carbaryl.
Leaves are mottled and yellowing, and a puff of white insects arises
if the plant is tapped.
Whiteflies are tiny white insects that feed on plant sap. Like
aphids, they excrete "honeydew" on which black mold may grow.
Control: Spray with insecticidal soap, pyrethrins,
malathion, or diazinon. You can also set out yellow sticky traps
whose color will attract them. The different stages of the
whitefly’s life cycle each have their own tolerance to insecticides,
so you’ll have to spray regularly and you may have to use more than
one control method.
Leaves are yellow; plant is stunted and wilts in hot weather.
Nematodes are microscopic worms that live in the soil and feed on
plant roots. If you pull the plant out of the ground, you’ll notice
that the roots are swollen and distorted.
Control: Destroy infested plants; plant resistant
varieties next season.
Symptoms: Leaves have light and dark mottling.
Cause: Tobacco mosaic virus.
Tobacco mosaic virus is very infectious and can be spread by simply
brushing against plants. The virus is seed-borne, but can also be
passed to the plant from tobacco in cigarettes and other products
(the virus actually survives tobacco processing).
Control: Destroy infected plants. Don't handle tobacco
before working around tomato your plants, and grow resistant
varieties next season.
Older, lower leaves are yellow; shoots or the whole plant wilts.
Cause: Fusarium, Verticillium, or
Walnut wilt. These three diseases are difficult to tell
apart. Fusarium and Verticillium wilt are caused by soil-borne
fungi, and walnut wilt comes from planting your tomatoes too close
to a walnut tree. The tree’s roots produce a chemical called juglone
which is toxic to tomato plants.
Control: After your harvest, destroy the plants. Next
season, plant varieties resistant to Fusarium and verticillium, and
practice crop rotation by growing your tomatoes in a different spot
in your garden each time. If you suspect Walnut wilt, next season
plant your tomatoes at least 50 feet away from your walnut tree, or
else grow them in containers.
Older leaves have dark brown, concentric rings on them. Or,
fruits have dark, leathery, sunken lesions at the point of stem
Cause: Early blight (also known as
Alternaria) Early blight occurs in humid weather. The
fungus overwinters in residue from diseased plants, and can also be
present on the seed itself.
Destroy or discard infected plants when harvesting is completed. In
the meantime, spray them with copper, chlorothalonil, mancozeb, or
maneb fungicides (look for the active ingredient on the label).
These sprays won’t cure the disease, but they can protect new
foliage from the fungus if they are used regularly all season.
**Thank you to
for these images
Leaves or fruit have irregular, greasy-looking or water-soaked gray
areas that expand rapidly in wet weather.
Cause: Late blight.
Late blight is the fungus that caused the great potato famine in
Ireland from 1845-1850. It occurs most often in humid weather,
during which a gray mildew grows on the undersides of the affected
leaves of tomato and potato plants.
Control: Spray with copper, chlorothalonil, mancozeb, or
maneb fungicides (look for the active ingredient on the label) to
protect new foliage. . You’ll have to continue your spray program
all season long. Destroy the infected plants as soon as harvest is
completed. If your plants are severely affected, dig them up and
destroy them immediately. ** thank you to
Cornell for image
Plant suddenly and rapidly wilts, even though the leaves are green
and it has been watered regularly.
Cause: Bacterial wilt.
This disease is caused by a soil-borne bacterium. It persists in the
soil in the southern states, and can be found in greenhouses in the
winter in northern areas.
Control: Dig up and destroy infected plants. Plant your
tomatoes in a different spot in your garden for a few consecutive
Circular or radial crack at the stem end of ripening fruit. Cracks
can extend deep into the fruit, causing it to rot.
Cause: Growth Cracks.
Tomatoes will crack when environmental conditions cause them to grow
rapidly during ripening. The rapid growth is frequently promoted by
a drought followed by heavy rain or watering. Cracking is more
severe in hot weather. Cracked tomatoes are edible.
Control: Maintain an even soil moisture level with
regular watering. Grow varieties that are labeled "crack
tolerant". *Thank you to
Colorado State for image
A round, sunken water-soaked spot develops at the blossom end
(opposite stem end). The spot enlarges, turns brown to black and
feels leathery. Mold may also grow on the rotted surface.
Cause: Blossom end rot.
This occurs from a lack of calcium in the developing fruits. The
first fruits of the season are the most severely affected. This
results from slowed growth and damaged roots caused by these
factors: 1. Extreme fluctuations in soil moisture 2. Rapid early
season plant growth followed by extended dry weather. 3. Excessive
soil salts. 4. Excessive rain. 5. Cultivating too close to the
Control: To prevent this problem, follow these
guidelines: 1. Maintain uniform soil moisture level by mulching
and proper watering. 2. Avoid high-nitrogen fertilizers or large
quantities of fresh manure. 3. Plant in well-drained soil. 4. Do
not cultivate within one foot of the plant. 5. Add gypsum to the
soil **Thank you to
Kansas State for image.
Sunken spots occur on ripe tomatoes. The centers of the spots
darken and form rings. Spots may merge, covering a large part of
This disease is caused by a fungus that rots ripe fruits. Infected
fruit is inedible. Fruit on plants partially defoliated by leaf
spot disease is prone to infection. Infections frequently become
epidemic in hot, rainy weather. Water from heavy dew, over-head
watering and frequent abundant rain provides the moisture necessary
Control: At the first sign of disease, spray plants
with a fungicide containing chlorothalonil. Repeat every 7-10 days
until harvest. Destroy all infected fruits. Clean up and destroy
plant debris after harvest.