USDA Sanitary Phytosanitary Project

CUCURBIT DISEASES I

Gummy Stem BlightFungus: Didymella bryoniaeDari

Pathogen/Disease description: Leaf lesions are tan to brown, dry and paper-like, often with concentric rings. As lesions enlarge the leaf develops breaks. Stem lesions often produce a brown gummy exudate. Small black spots (fungal fruiting structures) appear later in both stem and leaf lesions. Infections may kill young plants or cause cankers and wilt of older plants.

Cultural control: Rotate to other crops for 3 years, plow under crop residue in the fall, practice good sanitation if growing plants in greenhouse.

Chemical control: Use fungicide treated seed, Fungicides should be applied on a regular basis where this is a problem. The fungus may be resistant to several fungicides.

Fungal structures

USDA Sanitary Phytosanitary Project

CUCURBIT DISEASES II

AnthracnoseFungus: Colletotrichum orbiculareDari

Pathogen/Disease description: Lesions may appear on all above ground plant parts. Leaf lesions may cause distortion and shot hole symptoms. Infected fruit lesions begin as small black spot that may result in fruit abortion or distortion and decay. The disease is favored by rainy, humid weather and temperatures of 22-27 C.Cultural control: Use resistant varieties if available, rotate to other crops for 3 years, plow under crop residue in the fall, practice good sanitation if growing plants in greenhouse.Chemical control: Fungicides should be applied on a regular basis where this is a problem.

melon

melon

cucumber

USDA Sanitary Phytosanitary Project

CUCURBIT DISEASES III

Bacterial Fruit Blotch of watermelonBacterium: Acidovorax avenae subsp. citrulliDari

Pathogen/Disease description: On watermelon upper fruit surfaces develop water-soaked dark green patches. As the melon grows cracks develop and the entire melon may decay. May also cause smaller surface lesions on other melons.Cultural control: Use resistant varieties if available, rotate to other crops for 2 years, plow under crop residue in the fall, practice good sanitation if growing plants in greenhouse. Do not save seed from diseased plants.Chemical control: Fixed copper sprays, starting before fruit set, can help reduce spread but will not stop the disease during rainy weather.

USDA Sanitary Phytosanitary Project

CUCURBIT DISEASES IV

Fusarium wilt (watermelon, cucumber and melon)Fungus: Fusarium oxysporumDari

Pathogen/Disease description: Fusarium wilt is most severe in sandy, dry soils with a pH 5.0-6.0. Infected plants may die within 2-3 days or may be severely stunted. Plants often show wilt of one vine while the others remain healthy looking. Look for tan to brown discoloration in the vascular tissues of the stem below the wilting vines. The fungus is soil borne.Cultural control: Use resistant varieties if available, plant in new fields where melon has not been grown before, practice good sanitation if growing plants in greenhouse. Soil solarization may help reduce the fungus in the soil in some cases. Don’t save seed from infected plants.Chemical control: None available.

watermelon

USDA Sanitary Phytosanitary Project

CUCURBIT DISEASES V

Powdery MildewFungus: Sphaerotheca fuliginea and Erysiphe cichoracearumDari

Pathogen/Disease description: This common diseases attacks all cucurbits. White powdery like growth covers both top and bottom leaf surfaces, beginning on older leaves. The disease is favored by dry conditions at 20-27 C. The powdery mildew fungus that attacks cucurbits does not attack other kinds of plants. Powdery mildew on other plants is caused by other specific fungi specialized to the plant family.Cultural control: Resistant varieties are available for cucumber and canaloupe. Space plants well for good air movement. Chemical control: Fungicides should be applied on a regular basis where this is a problem. Sprays must cover both tops and undersides of leaves in the lower canopy.

USDA Sanitary Phytosanitary Project

CUCURBIT DISEASES VI

Bacterial wiltBacterium: Erwinia tracheiphiliaDari

Pathogen/Disease description: This disease severely affects melon and cucumber but may not be present in all regions. Single runners or the entire plant may wilt. Bacterial gum (ooze) is present in freshly cut stems. The disease is spread by the stripped cucumber beetle. Cultural control: Space plants well for good air movement. Use row covers until female flowers are open.Chemical control: Use insecticides to control the cucumber beetle.

gum/ooze

USDA Sanitary Phytosanitary Project

CUCURBIT DISEASES VII

Virus diseasesBacterium: At least 32 different virusesDari

Pathogen/Disease description: Many different viruses affect cucurbits. most are spread by aphids, infected seed or by mechanical means (contaminated hands or tools).Cultural control: Resistant varieties are available for some viruses. Control weeds. Reflective mulches can help repel some insect vectors. Plant early to allow fruit to mature before viruses become widespread.Chemical control: Insecticides to control the insect vectors are only slightly helpful.

USDA Sanitary Phytosanitary Project

CUCURBIT DISEASES VIII

Downy MildewFungus: Pseudoperonospora cubensisDari

Pathogen/Disease description: This is one of the most important and widespread diseases of cucurbits. The fungus may infect in dry climates if dew is present at 15-20 C. Symptoms: small yellow spots on upper leaf surfaces followed by gray to black fuzzy areas on undersides of leaves.Cultural control: Resistant varieties where available. Space plants for rapid leaf drying following rain or irrigation. Chemical control: Use systemic fungicides.

USDA Sanitary Phytosanitary Project

CUCURBIT DISEASES IX

Phytophthora blightFungus: Phytophthora capsici and other speciesDari

Pathogen/Disease description: Infected fruit develop discoloration followed by a soft rot and fuzzy gray growth on the soil side. Plants with crown infection wilt and die, often rapidly, especially in warm weather. The pathogen is soil borne and will remain in the soil for years.Cultural control: Long crop rotations, move to new fields.Chemical control: Use specialized fungicides.