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

Winter 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)

diseased squash leaves and 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 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 winter 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. Fruit lesions vary in size and may progress into flesh of fruit, causing them to rot.

Bacterial Wilt

herbivory on a cucurbit leaf
Cucumber beetle adults feeding on leaves. Photo courtesy of M.P. Hoffmann, Cornell University, NY.

Symptoms: Wilt starts on leaves which then develop interveinal necrosis. The petiole and vine eventually die back. Cucumber beetles are often found feeding on affected leaves.

Fungi & Oomycetes

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

diseased winter 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

diseased butternut 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 under 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 a 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 on stems, sometimes with gummy exudate. Pycnidia on leaves and stems. Fruit rot phase called black rot. Localized occurrence in region.

Phytophthora crown rot | See factsheet for more information

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

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

Plectosporium blight | See factsheet for more information (LIHREC)

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

Symptoms: Characteristic symptom is the diamond to spindle shaped white-tan dry and scabby lesions which are most distinctive on leaf veins and petioles, contrasting with the symptomless leaf tissue between veins. Lesions also form on vines, stems, petioles, fruit handles, and sometimes fruit.

Powdery mildew | See factsheet for more information

upper and lower sides of a diseased squash leaf
Photo courtesy of Meg McGrath, Cornell University, LIHREC, NY.

Symptoms: White, talcum-like, powdery fungal growth develops on both leaf surfaces and on petioles and stems. Symptoms usually develop first on older leaves, shaded lower leaves, and lower leaf surfaces. Powdery spots on lower surfaces may have yellow spots opposite on the upper leaf surface. Field-grown plants become susceptible when producing fruit or stressed. Infected leaves and plants senesce prematurely.

Scab

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

diseased butternut squash leaf and fruit
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.

Phytoplasmas

Aster yellows

diseased squash plant
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

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

diseased delicata squash leaf
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.

Zucchini yellow mosaic virus | See factsheet for more information (LIHREC)

diseased acorn 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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