Plant Disease Management Handbook

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Seed Crop, Crucifers (Brassica, Eruca, and Raphanus spp.) - White Leaf Spot and Gray Stem

By C. M. Ocamb

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Seed Crop, Crucifers (Brassica, Eruca, and Raphanus spp.) - Downy Mildew (Staghead)

By C. M. Ocamb

Image related to Radish (Raphanus sativus)-Downy Mildew

A daikon leaf with downy mildew.

Cynthia M. Ocamb, 2014.

A stem of a radish seed plant showing dark lesions due to downy mildew.

Photo by Cynthia M. Ocamb, 2020.

Note the white sporulation within the necrotic lesions on these radish seed pods.

Photo by Paul Koepsell, 1983.

Close-up of the downy mildew spores produced on daikon stems.

Photo by Cynthia M. Ocamb, Oregon State University, 2012.

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Seed Crop, Crucifers (Brassica, Eruca, and Raphanus spp.) - Chlorotic Leaf Spot (Light Leaf Spot)

By C. M. Ocamb

Cause Aphanomyces raphani, a fungus-like organism. The disease has been so severe in northwestern Oregon fields that the crop has been plowed under. The variety White Icicle is very susceptible. The fungus attacks primarily radish but also can infect many other crucifers.

Image related to Radish (Raphanus sativus)-Black Root

Note the necrotic areas on the roots.

Photo part of OSU Extension Plant Pathology Slide

Lesions are at first discolored, brown to bluish black then progresses to a blackened, constricted area.

Melodie Putnam, 1999.

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Seed Crop, Crucifers (Brassica, Eruca, and Raphanus spp.) - Black Leg

By C. M. Ocamb

Image related to Radish (Raphanus sativus)-Black Leg

Close-up of a leaf spot caused by Phoma lingam on a Brassica leaf. Note the tiny black dots which are the pycnidia.

Cynthia M. Ocamb, May 2014

Close-up of Brassica crop residue colonized by Phoma lingam and Leptosphaeria maculans.

Cynthia M. Ocamb, October, 2014

Cause The soft-rot bacterium, Pectobacterium carotovorum subsp. carotovorum (syn. Erwinia carotovora var. carotovora), enters through natural openings or wounds caused by insects and equipment. Pseudomonas spp. have been isolated from diseased roots and are thought to actively infect the host.

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Aster - Yellows

Cause A phytoplasma that is transmitted by the sugar beet leafhopper, Circulifer tenellus. Daikon appears more susceptible than round red varieties. Seed yield losses of 30% to 40% are common and are estimated to range up to 95%.

Cause Sclerotinia sclerotiorum is a fungus that overwinters as small black structures (sclerotia). Sclerotia may survive several years. After a moisture-conditioning period of at least 70 days, they produce a small, stalked, cup-shaped fruiting structure (apothecium), which releases spores into the air. Spores may infect senescent tissue such as blossoms and leaves or may germinate and colonize plant debris.

Cause Bremia lactucae, a fungus-like microorganism. The pathogen overwinters on wild hosts and weeds. It is worse in damp, foggy weather and between 43°F and 53°F.

Symptoms Light-green or yellowish areas on the upper leaf surface are matched by downy patches on the undersurface. Affected parts turn brown, and leaves die. Older leaves are attacked first.

Cultural control

Cause Fungus-like organisms Pythium debaryanum, Globisporangium irregulare (formerly P. irregulare), and G. ultimum (formerly P. ultimum) as well as the fungi Rhizoctonia solani and Fusarium spp.