Plant Disease Management Handbook

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

See:

Hemp (Cannabis sativa) - Verticillium Wilt

By C. M. Ocamb

A hemp plant showing wilting of entire plant.

Photo by C.M. Ocamb, Oregon State University, 2022

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 plant showing wilting and death on a portion of the shoot.

Photo by C.M. Ocamb, Oregon State University, 2022

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.

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

By C. M. Ocamb

See:

Greenhouse Plants, Ornamental - Gray Mold

Canker in the middle of the stem of this western hemlock was due to Botrytis.

OSU Plant Clinic, 2022.

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.

See:

Onion (Allium cepa) - Downy Mildew

Note These plants do not have a lot of problems and only a few samples have ever come into the OSU Plant Clinic. Cold winter temperatures well below freezing can cause minor bronzing to browning of leaves or serious defoliation depending on the weather conditions. Leaf browning can also occur to plants in full sun. Time of symptom development will help identify the cause. In some situations, plants in poorly drained areas may develop root rot.

Necrotic areas on older leaves indicates injury but unless we know when symptoms first occurred it could be either winter injury or summer heat stress.

Jay W. Pscheidt, 2022.

See:

Cherry (Prunus spp.) - Cherry Mottle Leaf

Cherry (Prunus spp.) - Eola Rasp Leaf (Yellow Bud Mosaic)

Several virus symptoms on one tree. Ringspots on the left side, vein clearing in the center (yellow rather than green leaf veins) and in the bottom right you can see a leaf with a line pattern (wavy or zig-zag line across the leaf blade).

Jay W. Pscheidt, 2020.

Cause Perreniporia subacida, a fungus, causes yellow root rot of several conifer species in Oregon and Washington. It is usually found on suppressed or weakened trees. It is rarely seen in vigorous trees. Hosts other than western red cedar include Douglas-fir, western hemlock, mountain hemlock, lodgepole pine, larch, and grand fir. Most infection results from contact by colonized roots with susceptible roots. Tree roots that are severely stressed appear to be most susceptible to infection and decay.