Plant Disease Management Handbook

Cause Pythium spp., Rhizoctonia solani, and Fusarium spp. Pythium is favored by cool, overly wet soil conditions, Rhizoctonia by warm soil temperatures.

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

By C. M. Ocamb

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

By C. M. Ocamb

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

By C. M. Ocamb

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Cantaloupe (Cucumis sp.)

Cause An oomycete, Pythium oligandrum, which forms durable resting spores resistant to heat (can withstand 194°F for 60 minutes). Problems develop when this fungus-like organism is present before spawning or introduced with the spawn; it does not seem to cause disease when introduced a couple of days after spawning. Pythium is commonly found in soil or associated with plant roots and is enhanced with wet soil conditions.

Cause A fungus, Trichoderma harzianum, that is common in soil and on organic matter. This fungus sporulates abundantly with sufficient light and the spores spread readily through the air or any mechanical means. Red pepper mites are often associated with this disease.

Cause A bacterium that can be mechanically spread by water, flies, mites, equipment, and workers. The bacteria can survive in debris and on surfaces, tools, and structures. Bacterial blotch disease of Agaricus bisporus and A. bitorquis is caused by Pseudomonas tolaasii. Burkholderia gladioli pv.

Cause Pseudomonas syringae pv. mori, a bacterium favored by cool, wet weather in spring. The OSU Plant Clinic has diagnosed this disease several times. Young leaves are more susceptible to infection. Bacteria appear to gain entry into the leaf by colonizing and destroying epidermal idioblasts (specialized leaf cells). Young idioblasts of mulberry do not have calcium deposits while older leaves have these concretions (cystoliths).

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Kalmia (Mountain Laurel)