University of Vermont Extension
Department of Plant and Soil Science
FOR THESE TOMATO PROBLEMS
Dr. Leonard Perry, Extension Professor
University of Vermont
If your tomato plants and fruits
aren’t looking as healthy as they should, perhaps with leaf spots or
fruits, they may have one of several diseases.
The disease that flared up a few
years ago in the Northeast, destroying many home and commercial
plantings, was late blight—the same fungal disease as gets on
caused the famous Irish potato famine in the mid-1800s. If you had
tomatoes with this, you may recall
the nickel-sized or larger spots, olive-green to brown, on leaves.
Sometimes the border of these spots is
slightly yellow or appears water-soaked.
Soon, brown to black lesions grow on stems with brown spots on
Late blight is often around but
conditions aren’t prime for it to spread and get out of control. If
it is present, sprays are available but
must be applied early in the season.
Once leaves are over about 10 percent affected, sprays do little
plants should be destroyed. Before doing
this, make sure you have this disease, checking with either the
Agriculture department specialists or those at the Plant Diagnostic
your state university (www.nephd.org).
If late blight has been present, you may try growing the resistant
‘Legend’ (a red slicing type) and ‘Juliet’ (a red plum cluster type
All-America Selections winner) among others.
Since it needs living material to overwinter, don’t save over tomato
plants and definitely not potato tubers in the ground.
Much more common on tomatoes (and
potatoes) is early blight, another but different fungal
disease. It causes leaf spots, stem
lesions, and fruit rots. The name is
deceiving as it more often develops not early but rather on mature
leaves. It usually progress up the plant, starting
first with older leaves near the base.
Spots may have concentric rings, giving a target or “bulls-eye”
appearance. Stem lesions often are
sunken with lighter centers. On older fruits, the dark and leathery
spots are often on the end attaching to the stem.
Rotating other crops for a couple
years in the same spot, particularly small grain cover crops, corn,
can help in control. Some cultivars
(cultivated varieties) have resistance to early blight (sometimes
Alternaria blight). Keeping up with
weeding and fertility, especially nitrogen and phosphorus, and
in the day so leaves dry quickly, all can help in avoiding early
blight. Sprays are available and ideally should be
started early in the season.
Septoria leaf spot, another fungal
disease, occurs under similar conditions as early blight and has
controls. Its spots are often gray or
tan, with darker margins, and have dark pimple-like structures in
that are fairly easily seen. These dark
fungal structures are absent from early blight lesions, nor do the
the target-like appearance.
If the fruits rot on the ends
opposite the stems, this is likely the common blossom end rot. It
is actually not caused by a disease, but
by the growing conditions-- uneven
watering and a calcium deficiency.
Especially if it is hot and dry, and then followed by heavy rain or
watering, this rot can develop as the plant can’t absorb enough
calcium. Other factors to try and avoid through
culture include low potassium or calcium levels, excess magnesium or
causing rapid plant growth, root damage, or high relative humidity.
Balanced watering and fertility, and perhaps
calcium sprays to foliage, should keep this under control on
tomatoes, as well
as on squash and peppers.
Verticillium wilt fungi are in the
soil, and if present can cause plants to wilt, beginning with lower
leaves. Lesions on leaves have a
V-shape, widest on the leaf margin. Leaves
die, and eventually the whole plant can die.
As there aren’t easy controls for this, crop rotation should be
practiced, and controlling weeds as many host this disease. There
are many cultivars with resistance to
Anthracnose is a fungal disease of
green, but especially of ripening, fruit.
Small, slightly sunken and watersoaked spots appear, that grow
and become dark in the centers. As it
spreads in the fruit it causes a softening decay. To avoid this
disease, grow plants on
well-drained soils, keep up with weeding, avoid excessive overhead
and rotate crops yearly. If present, you
may need to resort to sprays.
Visit the Cornell University
Vegetable MD Online for more information and photos on these and
of tomatoes, as well as of other vegetables (vegetablemdonline.ppath.cornell.edu).
always good to check with professionals, such as at local full
garden stores or plant clinics, to make sure your plants have a
disease before treating it. Cultural
controls and rotating crops, as mentioned, go a long ways to future
prevention. Also make sure you check
when ordering seeds or buying plants in the future that they have
some of the more common diseases. These
are indicated by letters in catalogs, such as for Fusarium (F) or
virus (TMV), and can be found in keys there to these code letters.