Originally prepared for Vegetable MD Online by Thomas A. Zitter.
This page includes symptoms caused by:
Bacteria
Bacterial wilt
Symptoms: Wilt initially affects single leaves as chlorosis followed by interveinal necrosis. It then progresses to individual runners of a plant. To test, cut stem, squeeze sap from the cut ends, place 2 pieces together, then slowly pull them apart while looking for characteristic thin strands of sticky bacterial ooze. Strands do not always form, so repeat several times until visible. Cucumber beetles may be currently (or previously) present 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: The circular leaf spots are initially water-soaked, then become yellow to tan. Round, black, sunken spots can develop on fruit. Whole leaves and vines can decline and turn necrotic.
Fusarium crown rot and wilt
Symptoms: Wilt initially affects single runners of a plant. Crown may be girdled. Distinctive dark brown decay at the base of the stem with white or pinkish fungal growth, becomes soft and mushy. Yellow, orange, or brown discoloration in water conducting tissue at the base of the plant. Fruit rot may also occur. This is localized in the field and region.
Gummy stem blight | See factsheet for more information (LIHREC)
Symptoms: Leaf spots are initially round or triangular when beginning at the leaf margin. They can rapidly enlarge and become irregular. Color is tan to brown. When seedling stems are infected the tissue often appears water-soaked and can lead to girdling which kills the plant. Petiole and stem tissues affected on older plants are water-soaked, tan, and develop a characteristic reddish brown gummy exudate. Tiny black specks, which are the pathogen’s fruiting bodies, develop on infected plant tissue including fruit.
Phytophthora crown rot | See factsheet for more information
Symptoms: Wilting and rapid plant decline. The vine will collapse and appear brown. Starts in areas with poor drainage after soil is saturated. Fruit rot may also occur. Dark leaf spots occur rarely. This is localized in the field and region.
Plectosporium | See factsheet for more information (LIHREC)
Powdery mildew | See factsheet for more information
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.
Ulocladium
Symptoms: Initial leaf lesions are reddish brown and 1-2 mm in diameter. Mature lesions increase to 6-7 mm and develop a beige center surrounded by dark brown halos or rings. Advanced lesions will break in the center and can resemble Angular leaf spot.
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.
More information:
- For more information, please contact:
Meg McGrath – mtm3@cornell.edu & Chris Smart – cds14@cornell.edu