Cucurbits (Cucumber, Melon, Squash, and Pumpkin)

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Leaf Disease

White, powdery dust


Powedery mildew on a pumpkin leaf.

Cause

Powdery mildew (Sphaerotheca fuliginea and Erysiphe cicoracearum), a fungal disease. Disease outbreaks are worse during cycles of warm days and cool nights.

Treatment

Plant resistant cultivars. Approved sulfur-based fungicides may also be used.

Brown leave spots that progress to holes


Melon leaf damaged by Anthracnose fungus.

Cucumber leaves with Anthracnose fungus.

Damage from the Anthracnose fungus on cucumber leaves.

Anthracnose damage on a melon.

Anthracnose-damaged squash.

Cause

Anthracnose (Colletotrichum lagenarium), a fungal disease that is most common in melons and cucumbers. Symptoms are often more common in humid, rainy weather.

Treatment

Use certified disease-free seed and plant resistant cultivars. Approved fungicides may be available. Consult your local Extension office for current recommendations.

Wilting leaves accompanied by sticky ooze from cut stems


Baterial wilt on cucumber.

A closer view of baterial wilt.

Baterial wilt vectored by the striped cucumber beetle.

The spotted cucumber beetle.

The spotted cucumber beetle.

The striped cucumber beetle.

Cause

Bacterial wilt (Erwinia tracheiphila), a disease spread by the spotted (Cerotoma trifurcata) and more commonly, the striped (Diabrothica vittatum) cucumber beetles.

The striped cucumber beetle is yellow or green in color and is roughly 1/4 inch long with three black stripes running lengthwise along the top of the body.

The spotted cucumber beetle is identifiable by the 12 black spots along its back.

Treatment

There is no treatment for bacterial wilt. Treatment is achieved by controlling the beetles which spread the disease. Inspect plants frequently. Approved insecticides include rotenone, malathion, and carbaryl.

Wet leaf lesions that become tan or white spots


Septoria fungus leaf damage.

Leaf damage from the Septoria fungus.

Cause

Septoria leaf spot (Septoria cucurbitacerum), a fungal disease that is often worse during rainy periods with high humidity.

Treatment

Use only certified disease-free seed. Rotate crops annually and remove crop debris at the end of each season. Approved copper-based fungicides are also available.

Stunted, dwarfed, mottled, or deformed leaves


Fruit mottled by cucumber mosaic virus.

Leaves damaged by mosaic virus.

Leaves damaged by mosaic virus.

Cause

Viruses. Cucurbits are often infected by several different types of viruses. Common ones include the Cucumber Mosaic Virus, the Watermelon Mosaic Virus, and the Squash Mosaic Virus..

Treatment

No treatment options exist after infection. Plant resistan cultivars and use certified disease-free seed.

Wilting leaves


Muskmelon damaged by root rot.

Root rot on a muskmelon plant.

Cause

Root rot cause by one of two fungal pathogens (Phytophthora spp. or Pythium spp.), usually in poorly drained soils.

Treatment

Remove infected plants and improve drainage if possible. Approved fungicides may also be available--contact your local Extension office for the latest recommendations. These pathogens may persist in the soil for many years.

Fruit Disease

Wet lesions


Anthracnose damage on a melon.

Anthracnose-damaged squash.

Melon leaf damaged by Anthracnose fungus.

Cucumber leaves with Anthracnose fungus.

Damage from the Anthracnose fungus on cucumber leaves.

Cause

Anthracnose (Colletotrichum lagenarium), a fungal disease that is most common in melons and cucumbers. Symptoms are often more common in humid, rainy weather.

Treatment

Use certified disease-free seed and plant resistant cultivars. Approved fungicides may be available. Consult your local Extension office for current recommendations.

Black lesions


Black rot damage.

Black rot damage.

Cause

Black rot (Didymella bryoniae), a fungal disease. Severity of this disease is often worse in hot, humid, and rainy weather.

Treatment

Use certified disease-free seed, rotate crops annually, and remove crop debris at the end of each season. Chlorothalonil and copper-based fungicides can be applied when disease symptoms first appear.

Mottled or deformed fruit


Fruit mottled by the cumcumber mosaic virus.

Leaves damaged by mosaic virus.

Leaves damaged by mosaic virus.

Cause

Viruses. Cucurbits are often infected by several different types of viruses. Common ones include the Cucumber Mosaic Virus, the Watermelon Mosaic Virus, and the Squash Mosaic Virus.

Treatment

No treatment options exist after infection. Plant resistan cultivars and use certified disease-free seed.

Insects and Insect Damage

Gray or black insects accompanied by yellow leaf specks leading to wilting


Squash bug (Anasa tristis).

Damage from the squash bug.

Damage from the squash bug.

Cause

The squash bug (Anasa tristis). The squash bug is related to the common stink bug and shares many of its visual characteristics. At around 1/2 inch in length when fully grown, the squash bug uses its piercing and sucking mouth parts to damage plants causing yellow specks which leads to wilting. Squash bugs may also damage fruit.

Immature squash bugs often have red legs and heads and their yellow, brown, or red eggs are often seen on the undersides of leaves.

Squash bugs are extremely common and are often seen near the base of the stem or on the undersides of leaves.

Treatment

Remove crop debris at the end of each season to reduce overwintering habitat. Treat plants with carbaryl or other labeled insecticides when there is more than one egg mass per plant.

Large holes at the base of vines accompanied by wilting


Adult squash vine borer.

Squash vine borer eggs.

Squash vine borer damage.

Squash vine borer.

Cause

The squash vine borer (Melittia cucurbitae), the larva of an unusual type of clear-winged moth which resembles a wasp. Squash vine borer larvae tunnels inside plant tissue causing damage.

Adults are roughly 1/2 inch long with red bodies encircled by black rings.

Treatment

Scout for adult moths from mid June to July using commercially available pheromone traps (type: EZAZ,13/ZZA 99:1).If adult moths are widespread in your area, apply approved pesticides such as carbaryl and permetherin to the base of the plant. Also remove crop debris at the end of each season to eliminate winter habitat.