Tomato factoids and diseases

[ICAN community coop]

http://www.coopext.colostate.edu/4dmg/Pests/Diseases/tomaprob.htm

Common Tomato Problems

By Judy Sedbrook, Colorado Master GardenerSM, Colorado State
University Cooperative Extension, Denver County

Looking forward to the flavor of a home-grown tomato after months of
the tasteless fare offered in grocery stores? Unless you are vigilant,
diseases, pests, and environmental problems can rob you of that
perfect tomato.

Diseases

Fusarium and Verticillium are soil-borne fungi that cause vascular
wilt diseases in tomatoes. They grow in the water-conducting tissues
of the plant. A close look will reveal brown discoloration in the
tomato's stem. Unable to receive nourishment through the damaged
vessels, leaves turn yellow and begin shriveling from the ground
upward and the plant dies (see above photo). There is no treatment,
but vascular wilt diseases can be prevented. The incidence of these
diseases has increased with the growing popularity of heirloom, non-
resistant, varieties. When choosing seeds or plants for your garden,
buy resistant varieties (labeled VFN). Rotate crops. Avoid planting
tomatoes, potatoes, or peppers in the same location for 3-4 years. Be
sure to remove and destroy all diseased plants.



Brown discoloration of stem with fusarium wilt

Tomato spotted wilt virus (TSWV) is an increasing problem in the home
garden. The disease begns with dark spots that form on leaves and
spread to stems, forming cankers. The affected side of the plant
develops bronzing of the leaves. The growing tips die back and the
growth of the plant is stunted. The fruit develops yellow spots and
rings in a mosaic pattern. There is no treatment for the infected
plants and they should be discarded.

TSWV is spread by western flower thrips. This insect is very difficult
to control. As weeds are often host plants to thrips, they should be
kept to a minimum in the areas surrounding the vegetable garden. When
planting your garden, be sure to buy certified virus-free seed and
plant varieties that are labeled for TSWV resistance.



Tomato Spotted Wilt Virus

Infection by the tobacco mosaic virus causes crinkling and light to
dark mottling of foliage. When cut open, the fruit shows browning
inside. This disease is easily spread by direct contact with tobacco
products or on the hands, clothing and tools of those who have handled
tobacco products. Be sure to wash your hands carefully before working
in the garden if you are a smoker. Choose plants that are labeled with
a 'T' after the variety. This indicates a higher resistance to the
tobacco mosaic virus. Infected plants and debris must be removed and
destroyed to prevent spread of the disease to healthy plants.



Tobacco mosaic virus symptoms (middle and right) compared with normal
foliage (left)

Septoria leaf spot and early blight occur less commonly in our dry
climate. These diseases result when soil is splashed up on the leaves
by rain or sprinklers. They can be prevented by mulching and avoidance
of overhead watering.



Septoria Leafspot

Insects

There are a number of insects that can cause tomato problems. Most
noticeable are the hornworms. These 3-4 inch caterpillars devour the
foliage near the top of the plant. They are easily picked off and
disposed of. Bacillus thuringiensis, rotenone or Sevin insecticides
can control them when they are small.

Aphids suck the juices from the plant. They can be found on the
underside of leaves and identified by the sticky honeydew they
produce. Aphids can be effectively controlled with insecticidal soap.

Psyllids, another small insect that sucks plant juices, are more of a
problem some years than others. They cause the foliage to turn yellow
and curl. Plants are stunted and often produce no fruit. Insecticidal
soap is also effective against psyllids.

Flea Beetles chew small holes into the leaves, leaving it looking as
though it had been "blasted" with fine shot.

Environmental problems

Distortion of the tomato is often the result of an environmental
problem.

With blossom end rot, a small water-soaked spot appears near the
blossom end of the tomato. As it enlarges, the spot becomes dark brown
to black, sunken and leathery. This happens when calcium is not
readily available to developing fruit. Calcium imbalance can result
from fluctuations in soil moisture caused by improper irrigation or
prolonged dry weather. Other causes are high nitrogen levels from
fertilizer, or a disruption of the root system. You can prevent
blossom end rot by the correct application of nitrogen, and keeping
the plants mulched to maintain moisture. Mulching also helps to
control weeds and eliminate the need for cultivation that can damage
roots.



Blossom End Rot

The sudden exposure of fruits to direct sunlight in hot, dry weather
can cause sunscald. This results in white or yellow patches on the
side of the tomato exposed to the sun. To avoid sunscald, limit
pruning and keep foliage healthy to provide shade and protection for
the ripening fruit.



Sunscald

Misshapen or malformed fruit can be caused by cool weather occurring
during fruit set or from herbicide exposure.

Catfacing is an abnormality that develops on the blossom end of
susceptible tomato varieties. It results from cool weather at blossom
time and causes the fruit to pucker and have deep crevices.



Catfacing

Growth cracks occur as a result of the rapid growth stimulated by wet
weather following a dry period. Two types of growth cracks affect the
stem end of tomatoes: concentric and radial. Concentric cracking
produces circular cracks around the stem end of the fruit. Radial
cracks spread outward from the stem scar.



Growth cracks

Leaf roll, or leaf curl, is a physiologic distortion that may develop
with periods of cool, rainy weather. It cause the lower leaves to roll
upward and become thick and leathery. Leaf roll does not affect plant
growth or fruit production and requires no treatment.



Leaf Roll

Herbicides can distort the foliage and fruit of tomatoes. They are
especially sensitive to 2,4-D. Damage can bend the leaves down,
causing cupping and thickening. New leaves are narrow and twisted and
do not fully expand. Fruit may be catfaced and fail to ripen. Exposure
can occur when herbicides are applied to lawns for weed control and
the spray "drifts". Resultant fumes can also effect the plants for
several days after treatment. Clippings from grass that has been
sprayed with a herbicide should not be used as mulch in the vegetable
garden. If the exposure is minimal, the plant will outgrow the injury.
Be sure to water the affected plants thoroughly and often.

Photo Credits

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