Pumpkin disease and rot.

Like all food crops, pumpkins are 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 plant 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.

Mulch. Mulch can help with water retention. Sand, mulch, and compost are all good options. Sand will keep down weeds but allow the free flow of water into the soil.

Watering. Water your pumpkins deeply about once a week (check the soil for dryness). Do not over-water. Soggy soil invites disease.

Other best practices include:

• Buy healthy, disease-free plants from reputable sources.
• Plant your pumpkins in full sun.
• Plant in sites with good drainage.
• Check plants regularly for signs of disease.

Alternaria leaf 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 annually; see crop rotation guidelines above

Anthracnose

Cause: Fungus
Symptoms:

• leaves turn yellow at the tips, eventually turning brown all around
• browned, dying leaves
• dark, sunken lesions on fruit and/or stems

How it spreads:

• spores spread by rain or splashing water
• wind

Treatment:

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

Prevention:

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

Bacterial wilt

Cause: Bacteria
Symptoms:

• leaves wilt and turn yellow; plant dies

How it spreads:

• striped cucumber beetle transmits bacteria when it feeds on stems and leaves

Treatment:

• destroy infected plants
• remove cucumber beetles

Prevention:

• use spunbonded row covers to protect plants from beetles
• plant in well-draining areas
• plant a decoy perimeter crop of Blue Hubbard squash to protect your pumpkin patch

Black rot

Cause: Fungus
Symptoms:

• black decay on pumpkins
• necrotic areas on leaves, often with yellow halos
• stem cankers with a brown gummy material

How it spreads:

• pathogen can be carried on the seeds or in the soil

Treatment:

• destroy infected plants
• apply liquid copper fungicide, if infection is severe

Prevention:

• use disease-free seed
• plant in well-draining areas
• rotate pumpkins and other cucurbits out for two years

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
• avoid overhead watering; water at soil level
• use homemade fungicides
• choose planting sites with good air movement and no shade
• rotate cucurbit crops out of area for two years

Plectosporium
Cause: Fungus overwinters on infected plant debris and in the soil, and emerges in warm, humid weather
Symptoms:

• small white diamond-shaped or lens-shaped lesions on vines, petioles, and leaf veins
• lesions coalesce on leaves and vines; foliage dies
• severely infected vines turn brittle and will shatter under pressure
• development of large, dry, scabby surface on fruit

How it spreads:

• fungus overwinters in infected plant debris and in the soil
• wind, insects, birds, and splashing water

Treatment:

• removed and destroy infected plant matter
• treat plant with protectant fungicide at the first sign of disease

Prevention:

• plant in sunny location with good drainage
• remove all plant debris at end of harvest
• rotate cucurbit crops out of area for two years

Phytophthora blight

Cause: Fungus-like organism, Phytophthora capsici

Symptoms:

• large, brown leaf spots
• rotting fruit
• crown rot
• dieback
• blackening of roots
• wilting plants
• bottom of leaves may have white spores
• fruit may also be covered in white spores as they rot

How it spreads:

• over-watered soil
• splashing of water from infected soil
• can live in the soil for years
• contaminated seeds

Treatment:

• remove and discard infected plant matter
• soil solarization

Prevention:

• use straw mulch
• apply liquid copper fungicide
• install drip irrigation
• plant disease-free seeds
• rotate cucurbit crops out of area for two years

Powdery mildew

Cause: Fungus overwinters on infected plant debris and emerges in warm, humid weather

Symptoms:

• white, powdery patches on leaves
• leaves may curl and turn upward
• new shoots appear stunted
• older infections look like a tan or reddish-brown felt covering; these contain spores
• heavy mildew infections can stunt a plant’s growth

How it spreads:

• fungus overwinters in infected plant debris
• spores do not need moisture to germinate; often called a “dry weather disease”
• wind, insects, and birds

Treatment:

• removed and destroy infected plant matter

Prevention:

• apply liquid copper fungicide
• if necessary, apply sulfur-based fungicide
• plant disease-resistant varieties
• remove all plant debris at end of harvest
• rotate cucurbit crops out of area for two years

Pythium fruit rot

Cause: Oomycetes
Symptoms:

• described as cottony leak or watery rot
• occurs during wet weather or in poorly-drained soil
• water-soaked lesions appear on fruit on or near the soil
• fruit collapses with a white cottony growth on the surface of the lesion

How it spreads:

• pythium species live in the soil or on other organic material
• high moisture allows infection to spread
• wounds in plants make them particularly susceptible

Treatment:

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

Prevention:

• plant in well-draining areas
• use drip irrigation; avoid overhead watering
• avoid excessive watering
• keep fruit off the ground by using mulch, stakes, or slings

Scab

Cause: Fungus

Symptoms:

• pale green, water-soaked lesions; these turn gray
• lesions may develop a yellow halo
• spots on fruit first appear as sunken areas often mistaken for insect injury
• spots may ooze sticky liquid, crater, and darken
• dark green layers of spores may appear
• numerous lesions may deform and twist leaves

How it spreads:

• fungus lives in the soil or on other organic material for up to three years
• fungus can become seedborne
• fog, heavy dew, light rain, and cool temperatures favor infection
• pathogen spreads on moist air, insects, gardening tools, and humans

Treatment:

• remove and discard infected parts

Prevention:

• apply protectant fungicide before fruit forms
• plant in well-draining areas
• use drip irrigation; avoid overhead watering
• avoid excessive watering
• plant disease-resistant cultivars

Which diseases have you had to treat on your pumpkins? Please tell us how you prevent and handle diseases.

If you spot other symptoms on your pumpkins that are not mentioned here, contact your local extension center or garden center for a consult—and please let us know what you discover by commenting below.