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.) - Sclerotinia Stem Rot

By C. M. Ocamb

Cause Phytophthora megasperma a fungus-like microorganism that survives as resistant spores in the soil and infects its hosts with swimming zoospores under wet conditions. All crucifer crops are susceptible, as are most cruciferous weeds.

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

By C. M. Ocamb

Cause The fungi or fungus-like microorganisms, Pythium spp., Fusarium spp. and Rhizoctonia solani, attack young seedlings of many vegetables, including members of the genus Brassica. These soilborne microorganisms can persist indefinitely in soil or plant debris. If seedlings are affected before emergence, it appears as poor germination.

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

By C. M. Ocamb

Cause Xanthomonas campestris pv. campestris, a bacterium that overwinters in plant refuse for up to 2 years and is carried internally and externally on seed. The bacterium infects other crucifer crops and weeds. It may be spread in the field by water (rain, irrigation), insects, equipment, and animals. Many outbreaks can be attributed to disease spread in the seedbed.

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

By C. M. Ocamb

Cause A bacterium, Pseudomonas syringae pv. maculicola, causes this disease, also known as bacterial leaf spot on cauliflower, broccoli, and Brussels sprouts. Bacteria survive on infested seed and crop residues as well as in soil. Cool, wet weather, common west of the Cascade Range, favors disease development before harvest in the fall.

Cause The phytoplasma 'Candidatus Phytoplasma phoenicium' subgroup 16SrIX-E has been associated with this problem. A witches' broom of western juniper (J. occidentalis) has been observed frequently in central Oregon. Trees with this problem seem to occur in known pockets. Affected trees do not have signs of rust or mistletoe.