Bacterial Leaf Blight of Carrots

Pathogen: Xanthomonas hortorum pv. carotae (Xhc)

Host Range: Carrots

Disease Distribution: carrot production worldwide

Seed transmitted, may contaminate carrot stecklings, may be found on carrot debris from previous crop

Bacterial blight occurs at high temperature (25-30C) and high relative humidity 

Overhead irrigation, rainfall, splashing water, and people, animals, and machinery can spread the bacteria in the field.

High risk pathogen for carrot seed production

•  Carrot seed must have less than xxx CFU/x amount carrot seed to get a PASS for market

Symptoms of Bacterial Leaf Blight

Early Symptoms: Angular yellow leaf spots

 Later Symptoms: Spots become irregularly shaped, brown and water soaked with yellow halos

Lesions occur mainly on outer margins of leaves: necrotic (dead)- brown to black color

Lesions develop on petioles- brown color, gummy exudate 

Symptoms on stalk and flower umbels: brown lesions that ooze yellow exudate

Bacterial Leaf Blight Field Diagnosis

Suspect plants can be tested in the field:

• immunostrips- follow instructions
• use carrot leaf tissue with symptoms
• positive result- 2 pink lines
• notify Monsanto- arrange for Monsanto to test the suspected plants

Is it bacterial leaf blight or herbicide, wind/frost damage?

1. Check for patterns in the field:

• Bacterial blight symptoms usually not found on every plant
• Symptoms first occur randomly on plant
• Herbicide/wind/frost damage will affect many plants at once- multiple rows of plants all with same symptoms (old and new leaves)
• Check to see if weeds have the same symptoms- indicates herbicide/wind/frost damage