Evaluating new biological and chemical controls for Pythium root dieback of carrot

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Pythium root dieback is an extremely destructive disease of carrots in many parts of the world and many regions of Canada, including Ontario and Manitoba. The disease is caused by the soil borne plant pathogen Pythium irregulare and a number of other, related Pythium species. These pathogens produce motile zoospores that are attracted to root exudates and can infect the root at any stage. When carrots are in the seedling stage, any damage to the developing root causes the root to stop growing and to produce several branched tap roots. The disease is called Pythium root dieback and the symptom is known as 'forking' and results in an unmarketable root. In fields with high populations of Pythium pathogens, complete crop failure can result from forking.