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)
Symptoms: Brown, angular lesions (restricted by small veins) often with yellow chlorotic halos. Young spots are water-soaked and older spots have holes in the center. Scab can cause similar leaf symptoms. Stems, petioles, and fruits develop water-soaked lesions that become covered with a white crust.
Bacterial leaf spot | See factsheet for more information (LIHREC)
Symptoms: Leaf spots are much smaller than those of Angular leaf spot and are often initially overlooked. The veins do not define the lesions shape and the yellow margin is indefinite. Fruit lesions will vary in size and may progress into the flesh of the fruit, causing them to rot.
Bacterial wilt
Symptoms: Wilt is accompanied by leaf marginal chlorosis and necrosis. The wilt then progresses quickly down the vine.
Fungi & Oomycetes
Alternaria leaf blight | See factsheet for more information (LIHREC)
Symptoms: Brown lesions with chlorotic halos, ranging 0.5-5 mm in diameter or greater. The spots often have concentric rings (target appearance).
Anthracnose | See factsheet for more information (LIHREC)
Symptoms: Tan to reddish ovular or circular lesions with visible pycnidia present. The lesions may have a light center that cracks, creating a shot-hole appearance.
Downy mildew | See factsheet for more information
Symptoms: Brown lesions that are angular and restricted by small veins. Young spots are pale-green to yellow on the upper leaf surface. Purplish or gray spores form on the underside of leaves. The leaves will turn necrotic and die while remaining erect, resembling frost injury.
Gummy stem blight | See factsheet for more information
Symptoms: Occasional marginal necrosis and larger, wedge-shaped necrotic areas with yellow halos may occur. Older spots are often dry and cracked. Spots and streaks on stems will develop, sometimes with a gummy exudate. Pycnidia will be visible on leaves and stems. The fruit rot phase is called “black rot.”
Phytophthora crown rot | See factsheet for more information
Symptoms: Dark brown lesions that can reach 5 cm in diameter. Whole plant decline and fruit rot are more common symptoms. Occurrence is localized in field and region.
Plectosporium blight | See factsheet for more information
Symptoms: Light tan lesions that are small, spindle-shaped, sunken, dry, and scabby. The spots are often on main leaf veins and occasionally on leaf blades, petioles, stems, and fruit.
Powdery mildew | See factsheet for more information
Symptoms: White, powdery-like spots first appearing on the underside of older leaves. Later, the characteristic white spots will occur on upper leaf surfaces.
Septoria leaf spot
Symptoms: White or beige circular lesions with a narrow brown border, reaching 1-2 mm in diameter or larger. In wet conditions, the spots can appear brown and water-soaked. Older lesions are typically cracked and have a few visible pycnidia. Fruit symptoms also occur.
Scab
Symptoms: Brown, angular lesions (restricted by small veins) that often have yellow halos. Young spots are pale-green and water-soaked. Older spots have holes in the center. Angular leaf spot can cause similar symptoms. These symptoms can also occur on petioles, stems, and fruit.
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
Symptoms: Yellowing of young leaves, proliferation of secondary shoots, and rigid, erect growth habit. Fruit symptoms also occur. Relatively uncommon.
Viruses
Cucumber Mosaic Virus | See factsheet for more information
Symptoms: Leaves mottled, distorted, wrinkled, curled, and dwarfed. Overall plant is stunted.
Tobacco Ringspot Virus | See factsheet for more information
Symptoms: Yellowish mosaic and interveinal chlorosis on infected leaves.
More information:
- For more information, please contact:
Meg McGrath – mtm3@cornell.edu & Chris Smart – cds14@cornell.edu