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Ministry of Agriculture, Food and Rural Affairs

Black Mold (Alternaria Fruit Rot)

Alternaria fruit symptoms Alternaria fruit symptoms
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Beginner

Scientific Name
Alternaria alternata

Identification

  • Initially, small, irregular tan lesions develop on the tomato fruit
  • These may develop into large, sunken, black lesions
  • In warm, humid weather, a black, velvety layer of spores may be produced
  • Black fungal growth may also develop on existing wounds or lesions

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 alternata

Identification
Initially, small, irregular tan lesions develop on the tomato fruit. These may develop into large, sunken, black lesions. In warm, humid weather, a black, velvety layer of spores may be produced.  Black fungal growth may also develop on existing wounds or lesions.

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.