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: Black root rot
Pathogens: Diaporthe sclerotioides (synonym Phomopsis sclerotioides)
Host crops: All cucumber cultivars are susceptible. Pumpkin and squash are much more tolerant than cucumber. The squash rootstock Cucurbita ficifolia is fairly tolerant. Black root rot of cucumber was first reported in North American in greenhouse cucumber production in British Columbia in 1972. The disease is a problem in greenhouse cucumber production in Europe and in cucumber fields in Japan. Cucumber root rot was found in cucumber crops in fields in northwestern Washington in 2012 and 2017. Cucumber plants start to wilt late in the season, usually after fruit have formed. Wilting develops rapidly over the whole plant, usually without yellowing (chlorosis) of the leaves. Symptoms on roots include salmon-colored to gray or brown lesions, often with black lines (pseudostromata) that demarcate infected areas of roots. Distinct, rectangular, black pseudosclerotia form in individual cells of the cortex. The crown and tap root of infected plants become dry and corky. D. sclerotioides occasionally forms black pycnidia in infected roots and crowns, within which only alpha conidia form (no beta conidia). In contrast, pycnidia produced by the cucumber Phomopsis fruit rot pathogen, Diaporthe cucurbitae, form both alpha and beta conidia. D. cucurbitae does not form pseudosclerotia or the characteristic black lines (pseudostromata) associated with cucumber black root rot. Cucumber black root rot is favored by acid soils (pH < 6.5), water deficit, heat stress, and development of fruit that increase transpirational demand on the root system.

Wilting of cucumber plants in a field in western Washington as a result of black root rot caused by <em>Diaporthe sclerotioides</em>. Distinct pink-brown to dark-gray lesions, some demarcated by black lines (pseudo-stromata), on the roots of a cucumber plant infected with the black root rot pathogen, <em>Diaporthe sclerotioides</em>. Distinct black lines (pseudo-stromata) formed by the black root rot pathogen, <em>Diaporthe sclerotioides</em>, in the roots of an infected cucumber plant. Distinct, rectangular pseudosclerotia in a secondary cucumber root infected with the black root rot pathogen, <em>Diaporthe sclerotioides</em>.
Wilting of cucumber plants in a field in western Washington as a result of black root rot caused by Diaporthe sclerotioides. Distinct pink-brown to dark-gray lesions, some demarcated by black lines (pseudo-stromata), on the roots of a cucumber plant infected with the black root rot pathogen, Diaporthe sclerotioides. Distinct black lines (pseudo-stromata) formed by the black root rot pathogen, Diaporthe sclerotioides, in the roots of an infected cucumber plant. Distinct, rectangular pseudosclerotia in a secondary cucumber root infected with the black root rot pathogen, Diaporthe sclerotioides.
Photo Source: Haruka Fukada, Washington State University

Online Resources:

Black Root of Cucurbits, Disease Guide, Seminis Vegetable Seeds, Inc.

Cultural control:

  • Do not plant cucurbits for consecutive years in the same field.
  • Use limestone to increase the soil pH above 6.5.
  • Avoid moisture stress.
  • Avoid moving soil from infested fields on equipment, shoes, vehicle tires, etc.
  • Remove diseased plants after harvest.
  • Rootstocks of the squash Cucurbita ficifolia are not as susceptible to cucumber black root rot as Cucumis sativa.

Chemical control:

Soil fumigation can reduce the population of propagules (pseudosclerotia and pseudostramata) of D. sclerotioides in the soil but will not eliminate the pathogen. Similarly, soil steam sterilization can control black root rot, although the fungus can reinvade steamed soil rapidly.

 


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