Department of Plant Pathology |
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| TOMATO DISEASES: FRUIT SPOTS AND ROTS |
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Fruit Spots and Rots frequently observed are
anthracnose, soil rot, early blight, late blight, buckeye
rot, blossom-end rot, bacterial spot, bacterial speck,
bacterial canker, and ghost spot.
Anthracnose
Early Blight
Late Blight
Buckeye Rot
Soil Rot
Bacterial Spot
Bacterial Speck
Bacterial Canker
Ghost Spot
Blossom-End Rot
Catface
Sunscald |
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Anthracnose,
a common rot on ripe fruit caused by the fungus Colletotrichum
coccodes, first appears as small slightly sunken circular
spots. Spots increase in size and the central portion darkens.
Anthracnose spots on a single fruit often expand, merge,
and cover a large area of the fruit. Spotted fruits may
rot completely, often as a result of attack by secondary
organisms. The anthracnose fungus overwinters in soil,
in residue from diseased plants, and on and in seed. The
fungus can become extablished on early blight leaf spots
and other dead areas on leaves. Fruit spots may develop
where the fungus is splashed to the fruit, either from
the soil or from plant parts. Green fruit can become infected,
although spots will not appear until fruit ripen. Disease
is prevalent on fruit that is overripe and in contact with
soil. Wet weather promotes disease development. |
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Early Blight, caused by the fungus Alternaria solani,
is more important on foliage than on fruit. On green
or ripe fruit, spots usually begin at the stem and and
develop into a black leathery sunken area, often with
dark concentric rings. (Leaf symptoms and disease cycle
information are presented in the section on Tomato Leaf
Spots and Blights.) |
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Late Blight is caused by the fungus Phytophthora infestans.
Although not common, it can be devastating on foliage
as well as fruit. Grayish green water-soaked spots enlarge
to indefinite size and shape on green fruit. Affected
areas become dark brown, firm, wrinkled, and have a relatively
definite margin. (See the section on Tomato Leaf Spots
and Blights for leaf symptoms and disease cycle information.) |
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Buckeye Rot is caused by the fungus Phytophthora parasitica.
It causes a fruit rot of tomato, pepper, and eggplant.
The first symptom is a grayish green or brown water-soaked
spot that usually occurs where the fruit touches the
soil. In warm weather half the surface area on fruit
may be affected. Dark zonate "buckeye" bands usually
are present within the affected area. Buckeye rot has
a smooth surface and lacks a sharply defined margin;
these features help distinguish buckeye rot from late
blight, characterized by a rouch surface and a definite
margin. The fungus lives in the soil. Disease is most
prevalent in poorly drained fields and in regions subject
to prolonged periods of warm wet weather. |
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Soil Rot caused by Rhizoctonia solani (which also
causes seedling damping-off), is characterized by slightly
sunken brown spots about 1 inch in diameter. Dark narrow-banded
concentric markings are distinct within new spots; later
the center of the spot often cracks open. The disease-causing
fungus is present in all field soil and affects tomato
fruit whenever conditions are favorable. Disease is promoted
by wet conditions and usually appears on ripe from in
contact with soil. |
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Bacterial Spot, caused by the bacterium Xanthomonas vesicatoria,
is characterized by a distinct fruit spot. Small dark
raised spots, sometimes surrounded by water-soaked margins,
appear on green fruit. Spots enlarge up to 1/4 inch in
diameter and become brown and scabby. (Leaf symptoms
and disease cycle information are presented in the section
on Tomato Leaf Spots and Blights.) |
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Bacterial Speck, caused by the bacterium Pseudomonas
syringae pv.
tomato, affects only tomatoes. Small black specks appear
on leaves, stems, fruit stems, and on fruit. The specks
on fruit are most characteristic; they appear on young
green fruit and are superficial, slightly raised, and about
1/16 inch in diameter. Tissue around fruit specks sometimes
remains green longer than the rest of the ripening fruit.
Disease-causing bacteria may overwinter on seed, in residue
from diseased plants, or in soil. The bacterium can be
introduced into fields on transplants. Wet cool conditions
promoted disease. Splashing rain and machinery movement
through fields assist spread and entrance of bacteria into
plants. |
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Bacterial Canker, caused by the bacterium Corynebacterium
michiganense, is discussed under tomato wilts. The
same bacterium also causes fruit spots. Spots are first
small
and whitish, but soon develop raised dark centers surrounded
by a white halo which later turns brown. |
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Ghost Spot appears on green tomato fruit as whitish rings
and spots 1/8 to 1/4 inch in diameter. These symptoms
mark the spot where a fungus (Botrytis) entered
the fruit but was killed by high temperature resulting
from sunlight on the fruit. Low temperatures and high
humidity promote fungus entrance into the fruit. |
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Blossom-end Rot, caused by insufficient calcium when fruit are
forming, is characterized by a large dry brown to black,
and often depressed, leathery area at the blossom end
of the fruit. Calcium deficiency usually results from
excessive nitrogen fertilization, rapid plant growth,
and drastic fluctuations in moisture as caused by heavy
rainfall, drought, and root pruning during cultivation. |
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Catface is
an abiotic disease caused by factors that seriously disturb
initial fruit development during blossoming. Symptoms are
extreme malformation and scarring frequently associated
with the blossom end. Two specific factors that may cause
catface are cool weather during fruit set and injury from
2,4-D herbicide. |
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Sunscald is
an abiotic disease caused by sudden exposure of fruit to
direct sunlight, particularly during hot dry weather. Leaf
blightrs and movement of foliage during picking often provide
conditions favorable for sunscald. Sunscald, most prevalent
on green fruit, appears as a whitish or yellowish patch
on the side of the fruit toward the sun. When sunscald
is severe, the affected area shrinks and forms a large
flattened grayish white spot with a paper like surface. |
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