Plant Disease Management Handbook

Cause Alfalfa mosaic virus (AMV), which is transmitted by aphids and can be seedborne. This virus has a broad host range (attributed to multiple species of aphid vectors) and infects at least 430 species of 51 dicot plant families including alfalfa (some varieties are asymptomatic), beans, clover, pea, potato, and tomato. Cilantro plantings were found infected with AMV in western Oregon during 2017. Subsequent testing of samples of seed planted in affected cilantro fields showed AMV to be present in seed samples.

Cause Several organisms can cause lower stem and root rots on these holiday cacti including Fusarium oxysporum, Pythium spp., and Phytophthora sp. The OSU Plant Clinic has found Fusarium.

Stems on the right side of this holiday cactus have collapsed indicating lower stem and root rot. Also, note the flower buds on the left side of the plant that have developed late October to early November in response to the shorter day length.

Jay W. Pscheidt, 2022.

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Peach (Prunus persica) - Wood Decay

Cut limb of this cherry branch shows the fruiting bodies of Trametes versicolor indicating wood decay.

Jay W. Pscheidt, 2015.

Wood decay can been considered when fungal fruiting bodies are observed on trunks and limbs.

Jay W. Pscheidt, 2008.

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Cherry (Prunus spp.) - Stem Pitting

Cherry (Prunus spp.) - Rasp Leaf

Cherry Cultivar Susceptibility

Leaf enations on small leaves of Bing cherry. Enations (small epidermal outgrowths) develop on the underside of these leaves adjacent to the midrib.

Jay W. Pscheidt, 2016.

Unlike other strains of TomRSV, trunks may develop only scattered pockets of shallow pits in the vascular cambium area.

Jay W. Pscheidt, 2017.

Note that most of this tree has rosetting (compressed) shoots while one branch to the right side has normal shoot and leaf growth. Tree was positive when testing for both ToRSV and PDV.

Jay W. Pscheidt, 2017.

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Cedar, Western Red (Thuja plicata) - Pencil Rot (Brown Pocket Rot)

Fir, Douglas and True - Stem Decays (Heart Rots)

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Oats (Avena sativa) - Crown Rust

Cause Several different fungi can cause leaf spots on cascara (sometime called buckthorn and formerly Rhamnus purshiana).

Rust (likely Puccinia coronata) fruiting bodies can be seen on leaves with pycnia on the top surface and aecia on the lower surface.

Jay W. Pscheidt, 2021.

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

By C. M. Ocamb

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Raspberry (Rubus spp.) - Root Rot

Note: The disease has been found mostly on newer cultivars such as Black Diamond and Columbia Star but also on Kotata.

This 'Chester' blackberry had Phytophthora root rot.

OSU Plant Clinic image, 2010.

Note: There have been low levels of nematodes found in the few samples that have been submitted from blackberry. Nematodes have not been an issue in blackberry as they have been in such crops as raspberry.

Cause Two types of wood decay occur in living trees: white rots and brown rots. The more common fungal white rots in birch are caused by Ganoderma applanatus, Fomes fomentarius, and Phellinus igniarus. White rots cause all major structural components of the cell wall-cellulose, hemicellulose, and lignin-to degrade. The strength of white rotted wood decreases only in advanced stages of decay.

Fungal fruiting bodies indicate colonization of the heart wood.

Jay W. Pscheidt, 2021.