Plant Disease Management Handbook

Cause Alkali yellows is caused by strongly alkaline soil, which can make iron or manganese unavailable to plants. Although soil pH may be the main problem, iron could be lacking in the soil or in a form unavailable to plants. A frequent problem sent into the OSU Plant Clinic from areas east of the Cascade Range.

Cause Xanthomonas campestris pv. incanae, a bacterium that persists in the soil, on or in seed. A vascular disease of the main stem and lateral branches. It often extends into leaf petioles and seed peduncles. Bacteria may be spread rapidly by splash from irrigation water. Cool wet weather favors infection and disease development. Yield losses of up to 90% have been experienced.

Cause Turnip mosaic virus has been reported from California for the perennial Limonium perezii. This disease has been sap- and aphid-transmitted to L. sinuatum. The disease spread rapidly, producing irregular patterns in the field. Several other viruses in Europe on the annual L. sinuatum include broad bean wilt virus, cucumber mosaic virus, statice Y virus, tobacco rattle virus, and tomato bushy stunt virus.

See:

Greenhouse Plants, Ornamental - Gray Mold

Cause Colletotrichum gloeosporioides (sexual: Glomerella cingulata), a fungus that survives on infected plants and plant debris. Some reports indicate the fungus may be seedborne. Wet weather and overhead irrigation favor the disease. Spores are produced in abundance within lesions. 'Gold Coast' is very susceptible.

See:

Squash (Cucurbita spp.) - Curly Top

See:

Watermelon (Citrullus sp.) - Verticillium Wilt

By Cynthia M. Ocamb and Hannah Rivedal

Cause The fungus, Septoria cucurbitacearum, can infect leaves and fruit and many cucurbits. It was found in zucchini fields in the Willamette Valley during 2004. The fungus survives on host debris for more than a single year as mycelium. Pycnidia are produced on infested debris and then form conidia, which are moved by splashing or wind-blown rain. Disease is favored by cool, wet weather in the spring or late summer.

Cause The fungus, Sclerotinia sclerotiorum, has been observed frequently in Oregon, particularly on zucchini and kubocha squash. This fungus overwinters in soil as sclerotia or on old infected plant material. The greatest losses are in pumpkins or squash piled in the open, or in storage, following preharvest infection. In storage, the disease is called watery soft rot.