Originally prepared for Vegetable MD Online.
This page includes symptoms caused by:
Bacteria
Bacterial wilt
Symptoms: Wilt initially affecting single leaves, and begins as yellowing and then death of tissue between main veins, wile veins themselves remain green in color. Wilt progresses to individual runners of a plant. Cut stem, squeeze sap from cut ends, put 2 pieces together, then slowly pull them apart while looking for characteristic thin strands of sticky bacterial material. Strands do not always form, so repeat several times until seen. Cucumber beetles often present (or previously) on leaves or in flowers.
Cucurbit yellow vine decline
Symptoms: Vines wilt and turn yellow in several days. Cross-sectioning of the stem will likely reveal a yellow discoloration of the phloem tissue which has become colonized by the bacteria.
Fungi & Oomycetes
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.
Fusarium crown rot and wilt | See factsheet for more information (LIHREC)
Symptoms: Wilt initially affecting single runners of a plant. Crown may be girdled. Distinctive dark brown decay a base of stem, with white or pinkish fungal growth, becomes soft and mushy. Yellow, orange or brown discoloration in water conducting tissue at base of plant. Fruit rot also present. Localized occurrence in field and in region.
Gummy stem blight | See factsheet for more information (LIHREC)
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
Symptoms: Wilting and rapid plant decline. Vine collapsed and brown. Starts in areas with poor drainage after soil was saturated with water. Fruit rot also. Dark leaf spots occur rarely. Localized occurrence in field and in region.
Plectosporium | See factsheet for more information (LIHREC)
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
Symptoms: White, powdery-like spots appearing first on the under surface of older leaves. Powdery growth then appears on upper leaf surfaces and can spread to stems.
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.
Phytoplasmas
Aster Yellows
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)
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)
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)
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)
Symptoms: Leaves mottled, distorted (sometimes fern-like), wrinkled, curled, dwarfed. Plant stunted. Fruit symptoms also present.
More information/prepared by:
- For more information, please contact:
Meg McGrath – mtm3@cornell.edu & Chris Smart – cds14@cornell.edu