Stem Rust:
essential data |
Disease Name, Other
Names, Crops Affected Causative
Agent, Synonyms,
Description
of the Agent Symptoms Prevention
and Treatment
Other Comments |
| Disease name |
Stem Rust |
| Other Names |
Black rust |
Causative Agent
|
Puccinia graminis f. sp. tritici |
| Synonyms |
Puccinia graminis |
| Crops Affected |
Wheat is the most important. Barley, oats and rye are
also affected along with some economically unimportant species of
grasses and barberry. |
| Description of the Agent |
P. graminis f. sp. tritici is a rust fungus, a member of
the Uredinales and ultimately members of the basidiomycetes (the club
fungi, including the mushrooms). They are called rust fungi because
disease plants show rust-colored orange patches on the infected plant
parts. In addition to structural features that are typical of basidiomycetes,
they have a complex life cycle with up to five forms of spore being
formed. It is one of these forms, the uredospore, that is rust colored.
The spores are easily spread by the wind and are brought out of
the air by rain. They can survive the harsh winters of the US Great
Plains but need relatively warm weather to germinate. |
| Symptoms |
The disease is first seen as elongated elliptical blisters on the
leaves and stems of the plant running parallel to the long axis of
the leaf or stem. These break open some days later to reveal a mass
of rust-colored spores. Later in the season, a new spore type, the
telospore, forms and the lesions turn black. Crop losses can reach
15-20%. |
| Prevention and Treatment |
Cultural practices, such as crop rotation are of no
great help, but barberry bushes should be eradicated from the area
as they can act as an intermediate host. Planting of resistant varities
of wheat is the best practice.
Effective fungicides include:
- Dichlone,
- Propaconizole,
- Sulfur
- Tridemefon,
- Zinc/maneb mixtures,
- Zineb.
These only need to be used when the risk of large-scale outbreaks
is high because they are not particularly effective and need repeated
applications. |
| Other Comments |
The disease is dependent upon relatively high temperatures
(daytime highs of 21°C or 70°F) and rain or heavy dews for
germination. It is widespread.
Strains of the fungus are specific for certain strains of wheat
and careless use of wheat strains resistant to a specific form of
the fungus can lead to the rapid development of new forms of the
fungus attacking the resistant wheat that can give rise to epidemic
outbreaks. |