Beginner

Scientific Name
Alternaria tomatophila, Alternaria solani

Identification

• Circular to angular spots with dark, concentric rings (target spots) develop on the older foliage
• Severe infections spread to younger leaves
• Lesions become quite large and are often associated with considerable leaf yellowing
• Fruit infections are not common, but may appear as a blackened area at the stem-end or dark blotches and sunken areas (see Black Mold)

Often Confused With
Bacterial Canker (Early blight may cause browning of leaf edges, similar in appearance, but a lighter brown than bacterial canker symptoms.)
Septoria Leaf Spot (Early blight lesions grow much larger than Septoria lesions.)

Period of Activity
Early blight overwinters in infected crop residue and can be carried by infected seed and weed hosts. Spores are present throughout the growing season and may be carried long distances in the wind or spread by splashing water. Temperatures of 17- 24°C (63- 75°F) and extended leaf wetness favour early blight development.

Scouting Notes
Early blight lesions can be distinguished from other lesions on the foliage by the presence of concentric rings. 

Thresholds
Where available use the TOMcast program. If this is unavailable, begin a preventative spray program when the first fruits are about walnut size.  Repeat sprays as necessary.  Repeat at 5- 7 day intervals during continuous moist weather.  Extend the schedule to 12- 14 days in warm, dry weather if diseases are under control.  Applications should continue until close to harvest. 

Advanced

Scientific Name
Alternaria tomatophila, Alternaria solani

Identification
The first signs of disease often appear deep in the canopy where the leaves stay wet. Lesions first appear on leaves as dark brown to black spots, 8- 13 mm (5/16- 1/2 in.) in size, on older foliage, but can grow much larger. Spots are circular to angular with dark concentric rings (target spot). The tissue surrounding the spot may be yellow. Lesions become quite large and are often associated with considerable leaf yellowing. 

If the disease is severe, lesions also appear on younger leaves. As lesions enlarge, their shape may become irregular. They are often bordered by leaf veins. 

Early blight may cause browning of leaf edges. Lesions may coalesce to form large dead areas on the leaf. Lesions may also appear on stems and blossoms (a cause of blossom drop).

Fruit infection is uncommon, showing up as a blackened area, similar in appearance to blossom-end rot, but at the stem end of the fruit or as blotches or sunken areas (see Black Mold).

Often Confused With
Bacterial Canker (Early blight may cause browning of leaf edges, similar in appearance, but a lighter brown than bacterial canker symptoms.)
Septoria Leaf Spot (Early blight lesions grow much larger than Septoria lesions.)

Biology
The fungus that causes early blight survive on decayed plant material in soil and can be seed borne. It is spread by wind and splashing water. It can also be present on weed hosts.

Period of Activity
Spores are present throughout the growing season and may be carried long distances in the wind. Temperatures of 17- 24°C (63- 75°F) and extended leaf wetness favour early blight development. Unless the fungus is present on transplants, lesions generally don’t show up until flowering.

Scouting Notes
Early blight lesions can be distinguished from other lesions on the foliage by the presence of concentric rings. 

Thresholds
Where available use the TOMcast program. If this is unavailable, begin a preventative spray program when the first fruits are about walnut size. Repeat sprays as necessary. Repeat at 5- 7 day intervals during continuous moist weather. Extend the schedule to 12- 14 days in warm, dry weather if diseases are under control. Application should continue until close to harvest. 

Management Notes

• Reduce early blight inoculum by following a 3 to 4 year crop rotation.
• Ensure transplants are healthy and free of disease.
• Cultivars vary in tolerance to early blight.
• Overhead irrigation can promote foliar fungal disease due to longer periods of leaf wetness.