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Carrot black rot

Scientific Name
Alternaria radicina
Scientific Author
(Meier) Drechsler & E.D. Eddy
Taxonomy
(Deuteromycotina: Hyphomycetales: Dematiaceae)
Status
Exotic Species Occurrence in Australia
Reliability
High
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Distribution

  • Cosmopolitan

Description

In areas where carrots are grown, A. radicina  can exist in the soil for up to 7 years. It can be measured in colony forming units (CFUs) per gram of soil using a selective agar (Alternaria radicina selective agar, ARSA). Locations with levels above 20CFUs/g soil have the potential of cauing a disease occurrence in the filed (Pryor, 1994).

Overseas work has shown that an integrated disease management program for foliar infection by Alternaria was greatly enhanced by using resistant varieties in conjunction with mofified drip irrigation. This practice also reduced the frequency of fungicide foliar applications (Ben-Noon et al., 2003).

Carrot seed infested with A. radicina can be successful eliminated by using a hot water soak at 51oC for 30 mins or a steaming treatment at 51oC for 30 mins. Other seed soaks that reduce levels of Alternaria spp. in seed include Potassium permangantae soak (10g/L) at 22oC for 30 min, Hydrogen peroxide soaks at (3-6%) at 22oC for 10min and 0.1 -1.0% Sodium hypochlorite soaks at 50oC for 10 to 30 min . However some the latter treament reduces seed germination by up to 5%. Biopriming carrot seed with fungal antagonists such as spore suspensions of Gliocladium spp have successfully controlled seed-borne infestations of A. radicina (Knudson, 2003).

Spore suspensions of Gliocladium virens when applied to umbels in carrot seed crops controlled A. radicina infection in artificial infested seed, improved germination and seedling emergence (Coles et. al., 2003).

Field trials showed that the Amistar at a rate of 450g/Ha was consistently the most effective fungicide to control crown and petiole infection by Alternaria spp. It was also effective in controlling seed-borne infestations as a spray on seed crops and as a soak on artificially infected seed.


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