Carrot Leaf Blight

Cercospora carotae and Alternaria dauci fungi, and Xanthomonas carotae bacteria

Carrot leaf blight [Credit: Gerald Holmes, California Polytechnic State University at San Luis Obispo, Bugwood.org]

Carrot leaf blight [Credit: David B. Langston, University of Georgia, Bugwood.org]

Host Plants:

On Crops: Carrots

Where Found:

Worldwide, wherever host crops are grown

Description:

In mid to late summer when carrots have produced a lush canopy of foliage, a period of prolonged rain can trigger an episode of carrot leaf blight. Leaves and stems show dark reddish-brown spots, and leaflets wither at the tips. Problems worsen following additional rain or fog with temperatures between 18-24C (65-75F).

Damage:

As carrots lose leaf area to blights, the plants are weakened and may not reach full size. Frequently the weakened carrot stems will break off when you try to pull a plant from the ground, so carrots must be dug rather than pulled when they are ready to harvest.

Preventing Problems:

Always rotate crops, and thin carrots to proper spacing so they will get plenty of sun and fresh air. No carrot varieties are truly resistant to this disease, but some are more susceptible than others. Observe varietal differences in your garden, and replant varieties that show little or no spotting of leaves.

Managing Outbreaks:

Clip off blighted leaves, and pull any weeds that may be encouraging dank conditions. Dig and store carrots as soon as they are ready.

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