Beginner

Scientific Name
Alternaria solani, Alternaria alternata

Identification

• Fruit develop leathery or blackened areas, similar in appearance to blossom-end rot, but at the stem end of the fruit
• Fruit symptoms most common late in the season, especially in wet conditions
• Black fungal growth may also develop on existing wounds or lesions
• Overripe tomato fruit may develop black mold caused by another species, Alternaria alternata
• Symptoms can range from small, dark blotches to large sunken areas
• Lesions may develop soft, black fungal growth in warm, humid weather

Often Confused With
N/A

Period of Activity
This disease may be present whenever there is ripe fruit. It is uncommon unless many overripe fruit are present. It prefers warm, humid weather.

Scouting Notes
This disease is generally not of economic importance. When present at high levels, it can cause quality problems for processing tomatoes.

Thresholds
None established

Advanced

Scientific Name
Alternaria solani, Alternaria alternata

Identification
Tomato fruit infection by Alternaria solani is uncommon, showing up as a leathery or blackened area, similar in appearance to blossom-end rot, but at the stem end of the fruit. Fruit symptoms are most common late in the season, especially when extended wet periods occur at harvest. Black fungal growth may also develop on existing wounds or lesions. Overripe tomato fruit may develop black mold, caused by another species, Alternaria alternata. Its symptoms can range from small, dark blotches to large sunken areas.  In hot, humid weather, the lesions develop the soft, black fungal growth that gives the disease its name.

Often Confused With
N/A

Biology
Alternaria overwinters and survives between crops as spores and mycelium in plant debris and seeds. It is spread by wind and splashing rain. During periods of rain, heavy dew or where there is good soil moisture the fungus grows and sporulates. Moisture must be present for germination and infection to occur. The infection penetrates the host through wounds or natural openings, like stomata.

Period of Activity
This disease may be present whenever there is ripe fruit. It is uncommon unless many overripe fruit are present. It prefers warm, humid weather.

Scouting Notes

• This disease is generally not of economic importance. When present at high levels, it can cause quality problems for processing tomatoes.

Thresholds
None established

Management Notes

• Harvest scheduling to avoid holding overripe fruit in the field will reduce problems with black mold. 
• A high incidence of blossom-end rot provides an increased opportunity for mold growth.