HomePest managementKeys for Identifying Vegetable DiseasesCucurbit Diagnostic KeySummer Squash Disease KeySummer Squash Leaf Symptoms

Summer Squash Leaf Symptoms

Originally prepared for Vegetable MD Online by Thomas A. Zitter.

This page includes symptoms caused by:

Bacteria

Angular leaf spot | See factsheet for more information (LIHREC)

two diseased summer squash cotyledons
Photo courtesy of Meg McGrath, Cornell University, LIHREC, NY.

Symptoms: Brown spots, angular in shape (restricted by small veins), often with yellow haloes. Young spots are water-soaked. Older spots have holes in the center. Scab causes similar symptoms on leaves. Stems, petioles and fruits develop water-soaked spots that become covered with a white crust.

Bacterial leaf spot | See factsheet for more information (LIHREC)

diseased summer squash leaf
Photo courtesy of Meg McGrath, Cornell University, LIHREC, NY.

Symptoms: Leaf spots much smaller than those of Angular leaf spot, and initially may be over looked. The veins do not define the lesion shape, and the yellow margin is indefinite.

Bacterial Wilt

diseased summer squash plant
General chlorosis and collapse on summer squash infected with Erwinia tracheiphila. Photo courtesy of T.A. Zitter, Cornell University, Ithaca, NY.

Symptoms: Wilt starts on leaves which then develop interveinal necrosis. The petiole and vine eventually die back.

Fungi & Oomycetes

Alternaria leaf blight | See factsheet for more information (LIHREC)

diseased summer squash leaf
Photo courtesy of Meg McGrath, Cornell University, LIHREC, NY.

Symptoms: Brown spots, 0.5-5 mm or larger in diameter, with yellow halo. Spots often have concentric rings (target appearance). Uncommon.

Anthracnose | See factsheet for more information (LIHREC)

Symptoms: Tan to brown oval spots with pycnidia. Spots may have light centers. Spots on stems and petioles (shallow, elongated, tan) and also on fruit.

Downy mildew | See factsheet for more information

close-up of a diseased squash leaf
Photo courtesy of Meg McGrath, Cornell University, LIHREC, NY.

Symptoms: Brown spots, angular in shape (restricted by small veins). Young spots are pale-green then yellow on upper surface. Purplish or gray spores form on lower leaf surfaces. Leaves turn brown and die but remain erect, resembling frost injury.

Gummy stem blight | See factsheet for more information (LIHREC)

close-up of diseased cucurbit leaf
Photo courtesy of Meg McGrath, Cornell University, LIHREC, NY.

Symptoms: Occasional marginal necrosis and large, wedge-shaped necrotic areas. Yellow haloes may occur. Older spots are often dry and cracked. Spots and streaks occur on stems, sometimes with a gummy exudate. Pycnidia on leaves and stems. Localized occurrence in region.

Phytophthora crown rot | See factsheet for more information

diseased cucurbit leaf
Photo courtesy of Meg McGrath, Cornell University, LIHREC, NY.

Symptoms: Dark brown leaf spots, up to 5 cm in diameter. Growing tips will likely collapse. Plant decline and fruit rot are more common symptoms. Localized occurrence in field and in region.

Plectosporium blight | See factsheet for more information (LIHREC)

underside of a diseased squash leaf
Photo courtesy of Meg McGrath, Cornell University, LIHREC, NY.

Symptoms: Light tan spots, small, spindle-shaped, sunken, dry, and scabby. Spots on main leaf veins and sometimes leaf blades, also on stems, petioles, fruit handles, and sometimes fruit.

Powdery mildew | See factsheet for more information

close-up diseased cucurbit leaf
Photo courtesy of Meg McGrath, Cornell University, LIHREC, NY.

Symptoms: White, powdery-like spots appearing first on the under surface of older leaves. Powdery growth then appears on upper leaf surfaces.

Scab

diseased squash leaf and fruit
Photo courtesy of T.A. Zitter, Cornell University, Ithaca, NY.

Symptoms: Brown spots, angular in shape (restricted by small veins), often with yellow haloes. Young spots are pale-green and water-soaked. Older spots have holes in center. Angular leaf spot causes similar symptoms. Symptoms also occur on petioles, stems and fruit.

Septoria leaf spot

close-up of diseased squash leaf
Photo courtesy of T.A. Zitter, Cornell University, Ithaca, NY.

Symptoms: White or beige spots, circular, 1-2 mm or larger in diameter, with narrow brown border. Brown water-soaked spots under wet conditions. Older spots usually are cracked and have a few pycnidia. Fruit symptoms also present.

Ulocladium

Symptoms: Reddish-brown lesions can reach 6-7 mm in diameter with beige centers surrounded by a darker necrotic ring and brown halo. Lesions are similar in appearance to Angular leaf spot but do not develop the typical “shot hole” appearance.

Phytoplasmas

Aster yellows

diseased summer squash plant and fruit
Photo courtesy of T.A. Zitter, Cornell University, Ithaca, NY.

Symptoms: Yellowing of young leaves, proliferation of secondary shoots, and rigid, erect growth habit. Fruit symptoms also present. Uncommon.

Viruses

Cucumber mosaic virus | See factsheet for more information (LIHREC)

diseased squash leaves and fruit
Photo courtesy of T.A. Zitter, Cornell University, Ithaca, NY.

Symptoms: Leaves mottled, distorted (sometimes fern-like), wrinkled, curled, dwarfed. Plant stunted. Fruit symptoms also present.

Watermelon mosaic virus | See factsheet for more information (LIHREC)

diseased squash leaves
Photo courtesy of T.A. Zitter, Cornell University, Ithaca, NY.

Symptoms: Leaves mottled, distorted (sometimes fern-like), wrinkled, curled, dwarfed. Plant stunted. Fruit symptoms also present.

Papaya ringspot virus | See factsheet for more information (LIHREC)

diseased summer squash leaves
Photo courtesy of T.A. Zitter, Cornell University, Ithaca, NY.

Symptoms: Leaves mottled, distorted (sometimes fern-like), wrinkled, curled, dwarfed. Plant stunted. Fruit symptoms also present.

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