Plant Disease Management Handbook

Cause Botrytis cinerea (sexual: Botryotinia fuckeliana) and other Botrytis spp., fungi that colonize dead, dying, and wounded plant parts. From these infections they can attack healthy tissues. A moist, humid environment is ideal for pathogen sporulation and spread. Spore dispersal is stimulated by changes in relative humidity. Conidia may come from many sources in and outside the greenhouse.

Cause Berkeleyomyces sp. (formerly Thielaviopsis basicola) is a widely distributed root pathogen reported from at least 30 plant families, including many ornamental plants. Untreated or improperly treated field soil can be a source of T. basicola if used in potted-plant culture. Most soilless media including commercial peat moss are clean. T.

Cause A fungus, Dilophospora alopecuri, that infects fine fescue and overwinters in infested residues or soil and may be seedborne. Dark colored fruiting bodies (pycnidia) develop and aggregate between veins on older leaves and leaf sheaths. Conidia are produced and dispersed by rain splashing.

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Wheat (Triticum aestivum) - Take-all

Cause A fungus, Ustilago striiformis. Many common grasses are hosts, but damage is most severe in bluegrass (Poa),bentgrass (Agrostis), and orchardgrass (Dactylis). It can be a significant problem in pastures, causing a reduction in hay yield and quality. Affected plants are susceptible to root rots and drought stress; they may die during cold winter weather or hot, dry summer conditions..

Cause Puccinia striiformis, a fungus that overwinters on infected plants. In the Willamette Valley, stripe rust is a serious disease in bluegrass. It also attacks orchardgrass. An alternate host for stripe rust is unknown. This population of stripe rust does not attack wheat, or vice versa. In spring, primary infection is from windborne urediniospores produced on infected plants. Secondary spread continues from subsequent infections.

Cause Puccinia graminis subsp. graminicola, a fungus that overwinters as slow-growing mycelium in overwintering plants. Susceptible hosts include perennial ryegrass, tall fescue, Chewing's fescue, orchardgrass, bluegrass. The principal alternate host is barberry (Berberis spp.). In spring, the fungus resumes more vigorous growth and produces primary inoculum (urediniospores) that are windborne.

Cause Unknown, but it is suspected that physical damage caused by thrips as the females insert eggs individually through the epidermis of the stem opens up the stem area to invasion by pathogenic bacteria. If bacteria are responsible, they likely survive in infested residues. This problem has been observed since before the mid-1990s in orchardgrass but is not considered to be yield limiting.

Cause Several insects, including thrips, stem borers and plant bugs, cause physical damage and/or inject plant toxins during feeding. Poa species and, to a lesser extent, orchardgrass are affected. The fungus Fusarium poae is associated with silvertop but only after damage has been done.

Cause Myxomycetes (Physarum spp., Fuligo spp., and Mucilago crustacea) that live in the soil or thatch and are favored by wet weather and an abundance of leaf litter. The appearance of slime mold (sporangia) can cause great concern but is not considered a disease and will recede after 1 to 2 weeks. Sporangia persist in the soil or litter where they have fallen, and they germinate during or after wet conditions.