Moldy carrots

Like all food crops, carrots are susceptible to various fungal diseases. Your greatest weapons against these are best planting practices, which help prevent disease in the first place.

This is especially important, as there are no fungicides approved for home use for many diseases.

These best practices are aimed at producing strong, healthy plants that can withstand disease, and at avoiding situations that contribute to the development of disease. They involve keeping plants clean, dry, and undamaged.

Watering: Water your carrots deeply about once a week (check the soil for dryness). Better to do one deep watering a week than several shallow waterings. If you hit a dry spell, your carrot plants could bolt, at which point they’ll only be good for the flowers.

Mulch: Mulch can help with water retention—but be vigilant and check for insect or fungal activity.

Other best practices include:

• Buy healthy, disease-free seeds from reputable sources
• Plant your plant in full sun
• Plant in sites with good drainage; if planting in open ground, choose a higher spot for better drainage
• Inspect frequently and remove infected plant material

Common Carrot diseases

Here are some of the usual culprits that might infest your carrot plants. Remember, it’s important to remove and destroy any infected plant material to prevent the spread of disease once it’s found its way onto your plant.

Aster Yellows

Cause: Bacteria
Symptoms:

• hairy, bitter roots
• yellowed leaves

How it Spreads:

• spread by leafhoppers, which feed on the plant juices

Treatment:

• liquid copper fungicide, if infection is severe
• remove and discard infected parts

Prevention:

• reduce leaf litter and garden debris, where leafhoppers overwinter
• sticky traps to trap leaf hoppers
• break up compacted soil
• plant in well-draining areas
• put straw or aluminum foil under carrot plants to confuse leafhoppers
• sprinkle kaolin clay on plants to discourage leafhoppers

Damping-off

Cause: Fungi
Symptoms:

• water-soaked, decomposing seeds
• infected roots are gray and water-soaked
• seedlings that grow but then collapse and die
• older plants that get infected are severely stunted

How it Spreads:

• spores thrive in moist soil and cool temperatures

Treatment:

• liquid copper fungicide, if infection is severe
• remove and discard infected parts

Prevention:

• minimize soil moisture
• break up compacted soil
• plant in well-draining areas
• treat seeds with fungicides before planting

Downy Mildew

Cause: Fungi
Symptoms:

• pale spots or long pale patches on leaves
• gray-purple, fuzzy growth on leaf surface
• leaves turn pale, then yellow
• leaf tips collapse

How it Spreads:

• splashing water (rain, irrigation) disturbs spores
• cool temperatures favor growth

Treatment:

• destroy infected plants
• apply foliar fungicides

Prevention:

• purchase disease-free seeds
• plant in well-draining areas
• homemade fungicides
• choose planting sites with good air movement and no shade

Which diseases have you had to treat on your carrots? Please tell us how you prevent and handle diseases. If you spot other symptoms on your carrots that are not mentioned here, contact your local extension center or garden center for a consult—and please let us know what you discover.