Plant Disease Management Handbook

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Seed Crop, Crucifers (Brassica, Eruca, and Raphanus spp.) - Alternaria Diseases (Black Spot, Gray Leaf Spot, Pod Spot)

By C. M. Ocamb

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Astragalus (Astragalus membranaceous)

Notes Several root rots have been sent in on samples of H. calycinum (creeping St. John's Wort) from the PNW to the OSU Plant Clinic. Pathogens found cause common root rot diseases and include the water loving oomycetes Phytophthora and Pythium as well as Rhizoctonia and Fusarium. Some of these pathogens have been reported in California but none from the PNW.

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Maple (Acer spp.) - Leaf Scorch

Note: Hydrangea macrophylla is considered a heavy water user and wilts easily under water deficit and/or high heat, though differences among cultivars exist.

Wilting of these Hydrangeas during the June 2021 heat dome.

Jay W. Pscheidt, 2021.

Sunburn results in necrotic tissue on both flowers and leaves if not water during heat stress events.

Jay W. Pscheidt, 2014.

Note There have not many samples into the OSU Plant Clinic. Diagnoses include Pythium root rots, Colletotrichum leaf spots, and Septoria leaf spot.

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Hemp (Cannabis sativa) - Verticillium Wilt

By C. M. Ocamb

Wilted hemp plants. Note the root discoloration that also can occur on plants infected with a vascular wilt disease.
Wilted hemp plants. Note the root discoloration that also can occur on plants infected with a vascular wilt disease.

Wilted hemp plants.  Note the root discoloration that also can occur on plants infected with a vascular wilt disease.

Photo by Chris Sullivan, Woodstock Consulting LLC.

A hemp stem of a wilted planted showing disoloration of the vascular tissue that are along the outer portion of the stem.

A hemp stem of a wilted planted showing disoloration of the vascular tissue that are along the outer portion of the stem. 

Photo by C.M. Ocamb, Oregon State University, 2021.

A hemp stem of a wilted plant showing discoloration of the vascular tissues that are found towards the inner portion of the stem.

A hemp stem of a wilted plant showing discoloration of the vascular tissues that are found towards the inner portion of the stem. 

Photo by C.M. Ocamb, Oregon State University, 2021.

By C. M. Ocamb

By C. M. Ocamb

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Greenhouse Plants, Ornamental - Gray Mold

Cause An occasional physiological disorder of wine grapes marked by characteristic foliar symptoms early in the season. It may be associated with a disruption of healthy nitrogen metabolism in developing shoots. Symptoms occur in rapidly expanding tissues such as shoot tips and unfolding leaves and may vary in intensity with the timing and length of early-season low temperatures.

Curling of leaf blade with a necrotic region in the central vein near the petiole and leaf blade juncture on the underside of the leaf.

Patricia Skinkis, 2021.

Curling of leaf blades on many shoots.

Patricia Skinkis, 2021.