![](../images/070308pics/RR070727.jpg) Tomatoes showing disease stresses
By John
Fulton
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[July 07, 2008]
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 Septoria leaf spot. Blossom end rot seems
to have been running rampant on early tomatoes as well.
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Early blight, also known 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. The spots frequently
merge, forming irregular blotches. Concentric rings often form,
creating a "target" or "bulls-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.
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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 options are Daconil and maneb, which are easier to
find but probably won't give you as good a control. The final step
for future years is to practice at least a three-year rotation, with
good sanitation in the garden.
Blossom end rot is a nonpathogenic disease that is very common
during extended dry periods. It begins as light tan, water-soaked
lesion on the blossom end of the fruit. The lesions enlarge and turn
black and leathery. This can drastically lower the yield and lower
marketability of the fruits. Fluctuating soil moisture supply during
the dry periods and low calcium levels in the fruit are the major
causal factors. Control of blossom end rot consists of providing
adequate moisture from fruit formation to maturity and use of mulch
(grass clippings, plastic, straw, shredded newspapers or plastic) to
conserve moisture. Avoid frequent shallow watering. Water deep and
then wait five or more days before watering again. Proper mulching
increases the number of days between watering and evens out the
moisture supply.
[By
JOHN FULTON,
University of Illinois Extension, Logan County] |