| Early blight is a fungal disease, Alternaria sp., that
occurs on tomatoes throughout North America. Early
blight can affect seedlings but is generally observed
on older plants and is especially severe on plants of
poor vigor. Plants infected with the fungus can
display collar rust on the stems, infected older
leaves, and fruits that crack at the stem. Infection on
leaves is the most common symptom.
Symptoms and Diagnosis
The appearance of circular or irregular dark spots on
the lower, more mature leaves is one of the first
symptoms of infection. Eventually, the spots enlarge
into a series of concentric rings surrounded by a
yellow area. The entire leaf may be killed and will
drop off the plant. Early blight can result in
extensive defoliation, exposing fruit to sunscald and
reducing yields. This disease typically progresses
from the base of the plant, upward.
Life Cycle
Early blight spores survive on old plant debris or in
the soil. Spores are spread by wind and rain, but
occasionally, flea beetles transmit this disease. Fungal
spores enter a host through wounds in the plant
cuticle. Spores thrive in moist, warm temperatures
(80–90 degrees F) and can persist in partially
decomposed garden waste for at least a year.
Integrated Pest Management Strategies
1. Plant resistant varieties. Varieties such as ‘Early
Cascade’, ‘Floramerica’, ‘Jetstar’, ‘Manlucie’,
‘Supersonic’, and ‘Surecrop’ have some tolerance
to early blight. These varieties will require a
less intensive management program than
susceptible varieties.
2. Maintain plant vigor. Stressed plants are more
susceptible to early blight. Water the plants
regularly, but don't fertilize until the plants are
well-established and in full blossom. Do not
mulch until the soil is warm.
3. Do a thorough cleanup of the garden in the fall.
Remove plant debris or till it into the soil. Pull
weeds that compete for light, water, and nutrients,
especially nightshade, horse nettle, and other
weeds in the tomato family.
4. Rotate crops. Practice a 2- or 3-year crop
rotation. Avoid planting eggplant or potatoes
where tomatoes were last planted.
5. Avoid activity when plants are wet. Confine
staking and picking to times when foliage is dry.
Disease is more readily spread when plant foliage
is wet.
6. Protect clean foliage with a fungicide. Effective
fungicides include copper (Kocide), chlorothalonil
(Bravo, Daconil), mancozeb, or maneb. Apply at
fruit set and reapply every 7–14 days. | 
