Tomato Blight: Identification, Prevention, and Treatment

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Tomato blight refers to a family of pathogens, caused by fungus which spreads through tomato foliage, often during wet weather.
The two most ubiquitous varieties of tomato blight are the early blight, caused by fungal spores of Alternaria solani or Alternaria tomatophila, and late blight, caused by water mold spore of Phytophthora infestans.
Early blight, as the name suggests, usually strikes during early tomato season, while the late blight strikes in the mid-to-late season.

Tomato Blight Cultural Prevention


Moisture provides the perfect conditions for spores to multiply. Avoid watering your tomato plant from above.
Water the soil around the base of the plant to keep foliage dry.
Watering should also be done in the morning so the plant has a chance to become dry during the day.


Rotate tomato crops to different parts of your vegetable garden every year and do not plant near potatoes that are affected by blight.

Spacing and Pruning

Give tomatoes plenty of room to grown and stake them instead of caging them.
The airflow will keep the plants dry, and make it difficult for the rot to spread if they are spaced apart.
Pruning tomato plants will allow for better airflow and active growing plants


Mulching tomato plants deters the spread of spores, which causes early and late blight.
If the plant gets infected, the surrounding mulch may house spores, and it needs to be taken off-site and burned.

Organic Fungicides

Copper fungicides are also useful in fighting off early and late blight. Read the instruction label carefully and wear gloves to avoid getting fungicides on your hands.

Chemical Control

Chemical fungicides are very useful in fighting tomato blight.
However, it is important to rotate between different chemicals to avoid developing resistance in pathogens for certain fungicides.
Some active ingredients to control tomato blight include:

  • penthiopyrad
  • boscalid
  • pyraclostrobin
  • fenamidone
  • azoxystrobin
  • cymoxanil
  • famoxadone
  • fluxapyroxad
  • pyraclostrobin
  • pyrimethanil
  • difenoconazole
  • cyprodinil
  • mancozeb
  • zoxamide
  • mandipropamid
  • fludioxonil

Make applications of chemical fungicides when environmental conditions are favorable and repeat as necessary.
Click to access Source Information at USDA here

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