Early Blight of Tomato

  • Symptoms

  • Trigger

  • Biological Control

  • Chemical Control

  • Preventive Measures

Early Blight of Tomato

Alternaria solani

Fungus


In a Nutshell

  • Dark spots with white halos on the leaves.
  • Dark, concentric circles on the stems and on the fruits.
  • Tomatoes start to rot.

Hosts

Tomato

Symptoms

Symptoms of early blight occur on older foliage, stem, and fruits. On the leaves, gray to brown spots appear that gradually grow in a concentric manner around a clear center - the characteristic “bullseye” formation. These lesions are surrounded by a bright yellow halo. As the disease progresses, entire leaves may turn chlorotic and shed, leading to significant defoliation. The same pattern of dark concentric lesions with a clear center appears on stems and fruits. Rotting of tissues follows.

Trigger

Alternaria solani overwinters primarily on infected crop debris in soil or on alternative hosts. Lower, older leaves might catch the infection when in contact with contaminated soil. Warm temperatures (24-29°C) and high humidity (90%) favor development of the fungus. It penetrates the leaf epidermis directly or enters through leaf pores. A long wet period (or alternating wet/dry weather) enhances the growth of spore cushions on the leaf spots and the release of spores. The spores are spread via wind, splashing rain or overhead irrigation.

Biological Control

You can spray algal limestone or rock flour on infected plants.

Chemical Control

Rotate different chemical compounds to avoid resistance development. Apply treatments in a timely manner, taking into account weather conditions. Fungicides containing Copper, mancozeb, chlorothalonil, azoxystrobin, pyraclostrobin, trifloxystrobin, fenamidone have been successfully used to control Early Blight in tomato.

Preventive Measures

Use certified pathogen-free seed.,Use resistant tomato varieties.,Allow for good drainage and airflow and avoid overhead irrigation.,Use stakes to keep the plants upright or remove the lower leaves (to a height of 40 cm).,Use organic or plastic mulch.,Rotate with non-host plants.,Control susceptible weeds in and around fields.,Use plant fortifier.,Do not over-fertilize with potassium and maintain adequate levels of both nitrogen and phosphorus.,Remove all plant debris after harvest.