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February Highlights

Things to watch for during February

From our experience of samples we have received during February in previous years in the OSU Plant Clinic, this page will highlight some problems that may occur this month.

Fungal disorders

Jay Pcheidt encourages growers to look for signs of canker diseases such as Eastern Filbert Blight. There is time before bud break (mid-March) to remove cankers before the next diease cycle begins.

Melodie Putnam encourages vineyard growers to look out for symptoms of trunk disease while pruning. See our presentation about this issue.

Cindy Ocamb reports that Black leg (Phoma stem canker) is continuing to appear in disease outbreaks in fall-planted crucifers (Brassica crops) planted across the Willamette Valley.  The cool, wet conditions are perfect for black leg and outbreaks of Sclerotinia stem rot as well as other diseases.  Brassica seed and vegetable crop fields experiencing outbreaks of black leg appear to be more susceptible Sclerotinia stem rot (white mold), gray mold, and infection by other fungi and bacteria.  See recent images here.   In addition to control measures recommended here for Black leg and Sclerotinia stem rot, growers of fall-planted vegetable fields that are heavily diseased should undertake destruction of diseased plants to eliminate infected crop residues.  Crucifer crops should scouted and diseased plants should be rogued from the field, especially in certified organic production.  If leaf spots incited by Phoma lingam are detected early enough, removal of affected leaves, before the fungus grows from the leaf spot down the petiole to the stem, can protect the plant from further development of Phoma on stems.

Symptoms of light leaf spot are starting to appear in Brassica crops, both seed and vegetable crop fields.  Stunting of crop plants and leaf deformities which resemble virus infections, herbicide or frost injury are appearing.  Infections of crop plants began last fall via wind-blown ascospores formed on infected crops resides, and asexual spores will soon be forming, if not occurring already, and bring the risk of disease buildup in infected fields.  Destroy infected, overwintered vegetable crops where possible and eliminated infected crop residues.  Control of crucifer weeds and volunteer Brassica crops will help with management of light leaf spot and black leg.

Pink snow mold, caused by the fungus Microdochium nivale, is very common in winter in Oregon and Washington.  The disease survives in diseased grass and dead plant debris, and leaf to leaf spread is favored by repeated frosts, cold fogs, and light drizzling rain.

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pink snow mold
perennial ryegrass

In the mid Willamette Valley Douglas-fir and true firs can be affected by Rhizoctonia web blight. Silvery fungal strands cover and bind the needles, and needles turn brown and remain attached to the stems. This fungus can kill buds and twigs of grand fir.

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douglas-fir Rhizoctonia web blight

Sclerotinia crown rot and wilt may appear in clover plantings in early spring when new growth wilts, dies, and may be covered with a whitish mold. Hard, black, fungal bodies (sclerotia) about the size of wheat grains are produced in the moldy area associated with diseased tissue.

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sclerotinia crown rot and wilt

Black root rot is caused by a fungal pathogen that can affect many plants including ornamentals such as begonia, pansy, fuchsia, and geranium in the nursery and greenhouse. The fungal spores persist in soil, and soil based growing media may be a source of infection. Symptoms are like those for many root diseases (yellowing, stunting and wilting) but eventually the roots develop flat black lesions caused by the formation of spores on and inside the root.

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lavendaer black root rot

Viral disorders

Impatiens Necrotic Spot Virus can be devastating for greenhouse ornamentals. This virus used to be called the Impatiens strain of the Tomato Spotted Wilt Virus. The virus is spread by adult thrips that acquired the virus as larvae while feeding on infected plants. Young plants may be most severely affected and symptoms include necrotic spots on leaves, discolored areas along leaf veins, leaf yellowing, leaf distortion, and blackening of growing points.

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lobelia INSVlobelia

Abiotic disorders

Often at this time of year we would be alerting our clients to the disease issues associated with winter injury. Fortunately so far we have not experienced the type of weather that leads to such issues.

Bacterial disorders

Crown gall can significantly affect grape production on affected vines. The causal bacterium survives in plant debris, old gallls and infected vines, and enters the plant through wounds. Wounds caused by winter injury will make vines very susceptible. The bacterium induces gall formation in the plant tissue, especially at the crown, and galled vines grow poorly or die.

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see also "The Plant Clinic Year"