Diseased broccoli

Like all food crops, broccoli is susceptible to various fungal diseases. Your best 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 broccoli deeply about once a week (check the soil for dryness). Do not over-water; soggy soil invites disease.

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 plants from reputable sources
• Plant your broccoli in full sun
• Plant in sites with good drainage
• Proper winterization
• Harvest frequently and remove infected foliage and florets

Common broccoli diseases

Here are some of the usual culprits that might infest your broccoli plants. Remember, it’s important to remove diseased buds and leaves to prevent the spread of disease once it’s found its way onto your plants.

Clubroot

Cause: Fungus

Symptoms:

• rapidly wilting leaves
• gnarled and misshapen roots
• stunted growth

How it Spreads:

• soil
• wind
• water
• footwear

Treatment:

• remove affected plants; do not compost
• raise pH to 7.2
• sterilize soil

Prevention:

• purchase healthy, disease-free seeds and plants
• avoid planting in previously affected soil

Black Leg

Cause: Fungus

Symptoms:

• cankering
• slimy decay and severing of stem at base
• light brown, purple-rimmed lesions with small black dots

How it Spreads:

• rain, splashing water
• wind
• gardening tools

Treatment:

• remove all infected plants

Prevention:

• rotate crops
• plant disease-free seeds and plants
• avoid water pooling under plants
• place plants to allow for air circulation and sunshine
• remove and safely dispose of affected plants including surrounding debris
• clean and sanitize tools regularly

Downy Mildew

Cause: Fungal-like water mold

Symptoms:

• seedlings turn yellow
• pale, angular spots on upper sides of leaves
• whitish spores on undersides of leaves
• gray to black spots on heads and dark streaks on stalks

How it Spreads:

• spores spread by rain, splashing water
• wind
• soil

Treatment:

• remove all infected parts
• apply liquid copper fungicide to reduce recurrence

Prevention:

• rotate crops
• avoid planting members of the same plant family (such as cabbage, cauliflower) near broccoli
• avoid water pooling under plants
• place plants to allow for air circulation and sunshine
• purchase disease-resistant varieties

Powdery Mildew

Cause: Moist conditions

Symptoms:

• ashy white powder on the top sides of foliage

How it Spreads:

• warm, moist conditions encourage spores that spread rapidly

Treatment:

• apply horticultural oils such as neem or jojoba
• introduce beneficial non-toxic organisms such as Bacillus subtilus

Prevention:

• avoid overhead watering
• water early in the morning
• keep plants appropriately fed and watered to maintain good health
• remove affected plants after the growing season to prevent spores from overwintering

White Mold/Sclerotinia

Cause: Fungal infection

Symptoms:

• stem appears to have a water-soaked part
• stems may have brown lesions from which cotton-like growth emerges
• leaves wilt, yellow, and die

How it Spreads:

• fungus releases spores that carry on the wind to infect plants, usually during cool weather

Treatment:

• destroy affected plants immediately
• remove any infected soil and replace with clean soil
• use a barrier, such as mulch or plastic to keep infected soil away from plants

Prevention:

• avoid overhead watering
• water early in the morning
• control weeds
• spray your plants with an approved fungicide to help prevent infection; spray the plants right before they bud, then spray again a week later
• remove affected plants after the growing season to prevent spores from overwintering

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