Disease-infected kale leaf

Like all food crops, kale is susceptible to various fungal diseases. Your most powerful 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.

Rotation: Even if you planted cole crops (Brassicas) in a particular place last season with no problems, don’t plant more cole crops in the same place two seasons in a row; in fact, you should give the soil a three to four year break from growing cole crops, just to protect your crops. Disease spores in the soil can persist, sometimes for years, and infect young plants.

Watering: Water your kale deeply about once a week (check the soil for dryness). Do not over-water. Kale, like most plants, hates having wet feet! 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 seeds or plants from reputable sources
• Plant your kale in full sun
• Plant in sites with good drainage
• Check your plants frequently and remove and destroy any infected leaves immediately
• Better to dispose of diseased plant material than compost it; you don’t want to perpetuate plant problems

Common kale diseases

It’s important to remove infected plants to prevent the spread of disease once it’s found its way onto your plants.

If you’re not sure what’s ailing your kale, take clear pictures of the affected plants and contact your local nursery or extension center. Be sure that if you go to a local nursery, you change out of your gardening clothes and shoes so you don’t inadvertently spread any bacterial or fungal infection.

Alternaria Leaf Spot (“Black Spot”)

Cause: fungi present after warm summer rain

Symptoms:

• small black dots appear on leaves, most obvious on the underside
• light spots with dark borders on leaves
• spots enlarge as disease progresses, forming a bull’s eye pattern
• leaves turn yellow between the infected spots
• will not kill the plant, but can significantly weaken it
• more than 12 hours of warm rain can distribute spores so much that the plant cannot recover

How it Spreads:

• rain helps spread spores in temperatures between 65 to 75 degrees F

Treatment:

• remove and discard infected leaves; this will reduce the number of spores and increase air circulation around plants

Prevention:

• buy disease-free seeds
• do not save seeds from infected plants
• avoid planting in cool, wet weather
• avoid overhead watering; water at soil level
• make sure plants have good air circulation and lots of sun
• rotate crops with non-Brassica species for three to four years

Anthracnose

Cause: fungus

Symptoms:

• leaves turn yellow at the tips, eventually turning brown all around
• browned, dying leaves
• dark, sunken lesions on leaves

How it Spreads:

• rain, splashing water
• wind

Treatment:

• remove all infected parts
• clear ground of leaf and twig litter
• apply liquid copper fungicide to reduce recurrence

Prevention:

• provide good air circulation and access to sunlight
• provide proper water and fertilizer

Bacterial Leaf Spot

Cause: Bacteria

Symptoms:

• leaves have circular spots with irregular edges
• spots may turn yellow and water-soaked
• leaf drop

How it Spreads:

• water
• wind
• garden tools
• thrives in warm, moist conditions

Treatment:

• remove and discard infected leaves
• if infection becomes serious, discard entire plant
• do not compost infected plant material

Prevention:

• mulch around plants to prevent water from splashing onto leaves
• avoid overhead watering; water at soil level
• make sure plants have good air circulation and lots of sun
• sterilize garden tools before and after each use
• spray plants weekly with neem oil or a commercial fungicide such as Bonide Revitalize
• rotate crops with non-Brassica species for three to four years

Black Rot

Cause: bacteria

Symptoms:

• irregular V-shaped yellow and brown patches appear on leaves
• leaves turn yellow; veins turn brown or black
• plant may appear lopsided as infection spreads
• can kill seedlings

How it Spreads:

• in seeds or seedlings
• infected garden tools
• insect damage
• bacteria favors high temperature and humidity
• bacteria can survive in residue of infected plant parts or infected weeds

Treatment:

• destroy infected plants
• bacteria can persist in the soil for up to two years

Prevention:

• purchase disease-free plants and seeds
• choose disease-resistant varieties
• water at soil level early in the day
• don’t work with plants when they’re wet
• with uncertified seeds, soak seeds in water for 35 minutes at 122 degrees F
• rotate crops with non-Brassica species for three to four years
• sterilize garden tools between uses
• wear clean gardening shoes and clothes
• practice good garden hygiene (no plant litter after harvest)

Clubroot

Cause: parasitic fungus

Symptoms:

• root distortion; swelling (galling)
• roots have a club-like appearance
• coral-shaped galls form on the roots

How it Spreads:

• spores move in water to infect roots
• spores can survive in the soil for more than 10 years
• resting spores can travel in drainage and irrigation water, infested soil, infected transplants, wind-borne soil particles, and infected soil on equipment, tools, and shoes
• prevalent where Brassicas grow, especially in humid, temperate regions

Treatment:

• destroy infected plants
• apply foliar fungicides

Prevention:

• purchase disease-free plants
• rotate crops with non-Brassica species for three to four years
• plant in well-draining areas
• use homemade fungicides
• increase soil pH to 7.1 to 7.5
• reduce soil moisture
• avoid planting in very wet soil

Damping-off of seedlings

Cause: fungus

Symptoms:

• rotting stems at or near the soil line
• moldy growth apparent at the soil line
• seed bed full of shriveled or stunted seedlings
• infected roots are gray and water-soaked

How it Spreads:

• spores thrive in moist soil and cool temperatures

Treatment:

• liquid copper fungicide, if infection is severe
• remove and discard infected parts
• increase air circulation
• increase light
• reduce watering frequency
• create better drainage

Prevention:

• sanitize seed trays between uses
• minimize soil moisture
• break up compacted soil
• plant in well-draining areas
• treat seeds with fungicides before planting, or purchase treated seeds
• maintain good light
• ensure good air circulation
• use sterilized soilless seeding medium

Downy Mildew

Cause: fungi

Symptoms:

• can affect seedlings or growing plants
• pale spots or long pale patches on leaves
• gray/white fuzzy growth on underside of leaves
• leaves turn pale, then yellow
• leaf tips collapse

How it Spreads:

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

Treatment:

• destroy infected plants
• apply foliar fungicides

Prevention:

• purchase disease-free plants
• rotate crops with non-Brassica species for three to four years
• plant in well-draining areas with good air circulation
• avoid overhead watering; water at soil level to avoid splashing
• water early in the day so leaves have a chance to dry
• use homemade fungicides

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