Reddish-brown cankers form near the tops of parsnips, parsley and carrot roots. Damage is usually only superficial, but can lead to secondary infections that cause root rot. Leaves and crowns can be infected too, but root cankers are the most serious.
Parsnip canker spores are released during periods of cool, wet weather and are spread by the wind to developing plants. Canker is a more severe problem on late-maturing varieties and on roots already damaged by carrot rust fly feeding. Parsnip canker overwinters in root pieces left in the soil and in carrot-family weeds growing nearby.
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