Extension Network Sites > Pacific Northwest Vegetable Extension Group > Photo Gallery of Vegetable Problems > Cucurbits > Watermelon

Watermelon

Diseases

Insect/Mite Pests

Abiotic Problems

Diseases

Curly top
Damping-off/Seedling blight

Verticillium wilt
White mold

Insect/Mite Pests

Wetern flower thrips

Abiotic Problems

Edema

(Click on photo to enlarge)

Diseases

Curly top

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.

curly top symptoms on acorn squash leaves — Squash, acorn
**Photo Source:** Phil Ham, OSU plant pathologist

symptoms of curly top on squash leaves — Squash
**Photo Source:** Phil Ham, OSU plant pathologist

Online Resources:

Pacific Northwest Plant Disease Management Handbook: Squash (Cucurbita spp.) – Curly Top.

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Damping-off/Seedling blight

Disease: Damping-off/Seedling blight
Pathogen: Pythium
Host crops: Most vegetables are susceptible to damping-off/seedling blight.

phthium root rot of watermelon — **Photo Source:** Lindsey du Toit

Online Resources:

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Verticillium wilt

Disease: Verticillium wilt
Pathogen: Verticillium species
Host crops: Numerous vegetables including many brassica vegetables (but not broccoli), cucumber,
eggplant, pepper, potato, pumpkin, radish, spinach, tomato, watermelon, etc.

symptom of chlorosis of watermelon leaves — Foliar chlorosis and early stages of necrosis associated with Verticillium wilt of watermelon.
**Photo Source:** Sacha Johnson

symptoms of verticillium wilt on watermelon leaves-1 — Partial foliar wilt associated with early stages of Verticillium wilt of watermelon.
**Photo Source:** Sacha Johnson

symptoms of verticillium wilt on watermelon leaves-2 — Complete foliar wilt associated with later stages of Verticillium wilt of watermelon.
**Photo Source:** Sacha Johnson

Online Resources:

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Insect/Mite Pests

Western flower thrips

Common name: Western flower thrips
Latin binomial: Frankliniella occidentalis.
Host crops: Basil, Cabbage , Cauliflower, Cucumber, Onion, Potato , Pumpkin , Squash , Tomato.

immature Western flower thips — 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.
**Photo Source:** Michael Bush, WSU Extension, Yakima, WA

Online Resources:

Western Flower Thrips Thysanoptera: Thripidae Frankiniella occidentalis (pdf).
Cucurbits: Thrips, UC IPM Online, University of California.
See Diseases, pests, and other problems common to many vegetables: Western flower thrips.

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Abiotic Problems Common to Cucurbits

Edema

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.

edema symptoms on pumpkin-2 — Close-up view of severe edema symptoms on a pumpkin.
**Photo Source:** Phil Hamm, Oregon State University.

edema symptoms on squash-1 — Small but extensive symptoms of edema on a winter squash.
**Photo Source:** Lindsey du Toit, Washington State University

edema symptoms on squash-2 — Close-up view of edema symptoms on the surface of a winter squash.
**Photo Source:** Lindsey du Toit, Washington State University

On-Line Resources:

OEDEMA – Ontario CropIPM, diseases-and-disorders.
Edema – Plant Disease and Insect Clinic, North Carolina State University.

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PDF Accessibility

If you need the content provided on this site in an alternate format or for further information on the Vegetable Seed Pathology program,

please contact: Lindsey du Toit at dutoit@wsu.edu or at 360-848-6140.

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