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Tomato diseases
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By John
Fulton
[July 10, 2007]
It seems like the tomato is the one plant that
just about everybody tries to grow. Some people grow large amounts,
while others plant one or two in containers. At any rate, the calls
and samples have started coming in to the office already. Most of
the samples have spots, brown leaves and dropping leaves, or all of
the above. Several diseases hit tomatoes, but two of the more common
ones are early blight and seporia leaf spot.
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Early blight, also know as Alternaria leaf spot, can affect
plants at any stage of development. All above-ground parts are
susceptible. The most characteristic symptom of early blight is
spreading spots, one-fourth to one-half inch in diameter, that
form on lower or older leaves. These spots have dark edges and
are usually brown to black in the center. These spots frequently
merge, forming irregular blotches. Concentric rings often form
creating a "target" or "bull's-eye" effect. Affected leaves
develop yellow areas around the lesions. Spotted leaves soon
turn yellow, wither and drop off. The fungus may cause lesions
on the fruit around the stem end and shoulder. The lesion is
usually dark brown to black, up to an inch in diameter and with
distinct concentric rings.
Septoria leaf spot can also affect plants at any stage of
development. Numerous small, water-soaked spots first appear on
the lower leaves. These spots soon become circular to angular
with dark margins and grayish centers, often bearing one or more
tiny black bodies called pycnidia, which are spore-bearing
structures. Individual lesions are seldom more than one-eighth
inch in diameter and are usually quite numerous on an infected
leaf. Heavily diseased leaves turn yellow, wither and drop off
in large numbers, starting at the base of the plant. Defoliation
can be severe during prolonged periods of warm, wet weather.
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 As for what to do, here is the checklist: First, keep ripe fruits
picked off the plants. Second, don't work around tomatoes when they
are wet. Next, you can try to improve air circulation, but if your
tomatoes are severely affected, you won't want to lose any more
leaves. And the final step for this year is to try a fungicide.
Mancozeb is probably the recommended one, but it is very hard to
find. The other option is use maneb or Daconil, which are much
easier to find but probably won't give you great control. The final
step for future years is to practice at least a three-year rotation,
with good sanitation in the garden.
Another disease that is actually an environmental problem is
blossom end rot. There have been several samples of this brought to
the office this year. The bottom of the tomato (the blossom end)
becomes dark and leathery. The condition is actually caused by a
calcium imbalance in the plant due to uneven moisture. The best
solution is mulching the area around the tomato with 2-4 inches of
mulch. Addition of calcium may or may not help the problem, but
almost certainly won't this late in the game.
That being said, enjoy those tomatoes!
[Text from file received from
John
Fulton, University of Illinois Extension,
Logan County Unit] |
