Pacific Northwest Vegetable Extension Group

of Washington State University, Oregon State University, and University of Idaho

Photo Gallery of Vegetable Problems

Cucumber

(Click on photo to enlarge)

Diseases

Disease: Angular leaf spot
Pathogen: Pseudomonas syringae pv. lachrymans

Photo of Angular leaf spot on cucumber
Photo Source: D.A. Inglis

Photo of Angular leaf spot on cucumber
Photo Source: D.A. Inglis

Photo of Angular leaf spot on cucumber
Photo Source: D.A. Inglis

On-Line Resources:

Pacific Northwest Plant Disease Management Handbook: Cucumber (Cucumis sativus) – Angular Leaf Spot

Cucumber, Pumpkin, Squash: Angular leaf spot, Washington State University Hortsense
 

Disease: Curly top
Pathogen: Various strains of Beet curly top virus (BCTV), which are vectored by the beet leafhopper (Circulifer tenellus)
Host crops: Numerous plant species including many vegetables such as bean, beet, carrot, eggplant, coriander, pepper, potato, tomato, various cucurbits such as squash, cucumber, pumpkin, watermelon, etc.

Photo showing symptoms of curly top on pumpkin leaves Phot of curly top symptoms on acorn squash leaves Photo of symptoms of curly top on squash leaves
Symptoms of curly top on pumpkin leaves. Note yellowing of the foliage. Squash, acorn Squash
Photo Source: Ken Eastwell, Washington State University virologist Photo Source: Phil Ham, OSU plant pathologist

On-Line Resources:

Pacific Northwest Plant Disease Management Handbook: Cucumber (Cucumis sativus) – Curly Top
 

Disease: Downy Mildew
Pathogen: Pseudoperonospora cubensis

Photo of angular, chlorotic lesions on the upper surface of cucumber leaves infected with downy mildew Photo of severe lesions on the upper surface of a cucumber leaf infected with downy mildew Photo of dark gray sporulation of the downy mildew pathogen in angular lesions viewed from the lower surface of a cucumber leaf Photo of dark gray sporulation of the downy mildew pathogen in angular lesions viewed from the lower surface of a cucumber leaf
Angular, chlorotic lesions on the upper surface of cucumber leaves infected with downy mildew. Note also the light gray downy mildew sporulation on the immature cucumber fruit to the right. Severe, angular, necrotic lesions on the upper surface of a cucumber leaf infected with downy mildew. Dark gray sporulation of the downy mildew pathogen
in angular lesions viewed from the lower surface of a cucumber leaf.
Photo Source: Lindsey du Toit, Washington State University
Photo of downy mildew sporangia on leaf surface Microscopic photo of downy mildew sporangia Microscopic photo of downy mildew sporangia
Closeup of sporangia on the leaf surface Microscopic photo of sporangiophores and sporangia of the cucumber downy mildew pathogen, Pseudoperonospora cubensis.
Photo Source: Jenny Glass

On-Line Resources:

Pacific Northwest Plant Disease Management Handbook: Cucumber (Cucumis sativus) – Downy Mildew

Cucurbit Downy Mildew News, Michigan State University.

Downy Mildew Control in Cucurbits, National Sustainable Agriculture Information Service

Downy mildew symptoms on cucurbit plants. Michigan State University.
 

Disease: Scab
Pathogen: Cladosporium cucumerinum

Photo of Scab on cucumber Photo of Scab on cucumber

Photo Source: D.A. Inglis

On-Line Resources:

Pacific Northwest Plant Disease Management Handbook: Cucumber (Cucumis sativus) – Scab {Gummosis}

Insect/Mite Pests


 

Common name (of damaging stage): Western flower thrips
Latin binomial: Frankliniella occidentalis.
Host crops: Basil, Broccoli, Cabbage, Cauliflower, Cucumber, Onion, Potato, Pumpkin, Squash, Tomato and Watermelon.

Photo of adult Western flower thrips Photo of immature Western flower thips Photo of thip damage to leaves Photo of thrip damage to cucumber fruit
Adult Western flower thrips are minute (less than 1/8 inch long) narrow-bodied insects that range from straw to dark yellowish-brown in color. Their four wings are very narrow and characterized by long fringed hairs. Immature Western flower thrips resemble the adults but are smaller, wingless and translucent yellow in color. There are multiple generations per year and thrips may invade vegetable fields when alternate flowering plants dry up in the summer or when an adjacent host crop is harvested. Thrips rasp (by puncturing individual surface cells and sucking cellular contents) the surface of fresh young plant tissues as they feed. Their feeding can weaken and deform flowers and cause a white specking or silvery discoloration on the underside of leaves. Under severe infestations, the specking can be seen as yellowing and fading of healthy green leaf color on the upper leaf surface as well. When given the opportunity, thrips will feed on the surface cells of cucumber fruit, leaving ghostly white stippling. This damage is cosmetic only, limited to the skin of the fruit. Early surface damage to the cucumber can appear as corky patches, negatively impacting the surface finish.
Photo Source: Michael Bush, WSU Extension, Yakima, WA

On-Line Resources:

Western Flower Thrips Thysanoptera: Thripidae Frankiniella occidentalis

Pacific Northwest Insect Management Handbook. Chapter: Vegetables, Section: Cucumber (garden symphylan to wireworm).

Pacific Northwest Insect Management Handbook. Chapter: Irish Potatoes, Section: Lygus bug to Thrips.

Pacific Northwest Insect Management Handbook. Chapter: Vegetables, Section: Broccoli, Cabbage Other Crucifers.

Vegetables: Bean: Thrips. Washington State University Hortsense.

Vegetables: Broccoli, Cole crops: Thrips. Washington State University Hortsense.

See Diseases, pests, and other problems common to many vegetables: Western flower thrips.
 

Abiotic Problems

Problem: Edema
A physiological problem: prominent when air is cooler than the soil, soil moisture is high, and relative humidity is high. The low plant transpiration rates combined with an increase in water absorption by roots from the soil leads to increased cell turgor pressure, resulting in eruption of epidermal cells as the inner cells enlarge. Protrusion of the inner cells causes epidermal cells to die and discolor, resulting in a ’warty’ appearance that can be misidentified as a disease. In addition to foliar symptoms on some hosts, many cucurbit crops develop wart-like protruberances on the fruit.
 

Severe wart-like growths on a pumpkin caused by edema Close-up view of severe edema symptoms on a pumpkin Small but extensive symptoms of edema on a winter squash Close-up view of edema symptoms on the surface of a winter squash
Severe wart-like growths on a pumpkin caused by edema. Close-up view of severe edema symptoms on a pumpkin. Small but extensive symptoms of edema on a winter squash.Close-up view of edema symptoms on the surface of a winter squash.
Photo Source: Lindsey du Toit, Washington State University. Photo Source:
Phil Hamm, Oregon State University.
Photo Source: Lindsey du Toit, Washington State University.

On-Line Resources:

http://www.omafra.gov.on.ca/english/crops/facts/00-031.htm#oedema

http://www.ces.ncsu.edu/depts/pp/notes/oldnotes/gp3.htm

Our pages provide links to external sites for the convenience of users. WSU Extension does not manage these external sites, nor does Extension review, control, or take responsibility for the content of these sites. These external sites do not implicitly or explicitly represent official positions and policies of WSU Extension.

WSU Mount Vernon NWREC, 16650 State Route 536, Mount Vernon, WA 98273-4768, 360-848-6120
Contact Us: Lindsey du Toit and Carol Miles