Alternaria radicina

Black rot of carrots

General

The only known stage in all Alternaria species is the asexual stage. Conidia and mycelium overwinter in the soil and on crop residues and cause primary infection of the leaves. Survival can be several years, in the case of black rot of carrots (Alternaria radicina) up to 8 years.

Life cycle and appearance of Black rot of carrots

Black rot of carrots (Alternaria radicina) is a seed-transferred carrot disease. The seeds are the main source of primary infection and this may lead to death of seedlings. From the primary infection of leaves, this type of carrot disease can spread to the flowers (especially dangerous in crops for seed production) and to the crown. Lesions of black rot of carrots (Alternaria radicina) may occasionally appear on the carrots at harvest but usually occur only during post-harvest storage.

Sporulation of Alternaria occurs at temperatures from 2-4 °C up to 28-30 °C (optimum temperatures lie between 15 and 28 °C) and at a relative humidity (RH) of over 90% or when the leaves are wet. Small differences in optimum temperatures occur between species, but in general, the risk of Alternaria infection is larger under quite warm and humid conditions. Infection may take place within a few hours, with lesions occurring as rapidly as two to three days later and sporulation within five days. Infection is both direct and through wounds and stomata. Spores are dispersed by wind and in some species through the splash of rain.

How to prevent Black rot of carrots

  • Remove crop residues, weeds and volunteer plants.
  • Use clean seed and propagation materials.
  • Practice crop rotation, in particular when spores surviving in the soil are the main source of infection. Especially wheat and barley reduce the number of surviving conidia in the soil.
  • Use resistant cultivars against black rot of carrots (Alternaria radicina).
  • Prevent damage during harvest (in potato and carrot).
  • Post-harvest storage at 0-1 oC.
  • A. brassicae and A. brassicicola: adjust the sowing date to avoid conditions conducive to infection.
  • In greenhouses: avoid high RH.

Prevent plant diseases by optimizing plant potential and crop resilience.