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February 2005. The American Phytopathological Society predicts a spread of rust diseases in the ornamental industry as plants ar shipped all over the country the risk of rapid spread of disease is substantial. There are 125 species of fungi that cause rust diseases reported on 56 different ornamental crops. Rust pathogens cannot be adequately detected on contaminated but symptomless plant material entering the US or moving state-to-state, and have the potential to dramatically affect ornamental crop production. Rust spores can easily lodge in the crown of plants that have had foliage removed for shipping purposes. Symptomless plants are then moved long distances through international or interstate trade, dispersing the pathogen and introducing it into areas that were previously pathogen-free.
While quarantine restrictions and eradication efforts are used to manage rust outbreaks and minimize potential disease loss, such efforts are not perfect and can have a significant economic impact on crop production. International trade of ornamental crops has made the exclusion of rust pathogens difficult because contaminated plant parts may be symptomless and inadvertently allowed to enter quarantined areas. With repeated introductions, pathogens may become widespread and cause the quarantine to fail.
A question was asked on PestNet whether countries are within their rights to required that imports of ormamentals come from certified rust-free areas.
In response, the following reply was received:
Of course authorities are entitled to take any action against a pest that is identified as meeting the criteria of being a quarantine pest for the importing country. Remember the neumonic EESEY.
- Entry
- Establishment
- Spread
- Economic
- YES for all these factors and it is a quarantine pest.
The issue with rusts is that they are complex diseases that may have different spore stages on the host, and also a life cycle that may require alternate hosts (i.e., different from the main economic host). The decision tree can be quite complex and authorities have to consider the specific host/pathogen relationship for each of the life stages of the pathogen, and sometimes have to consider the presence or absence of alternate hosts in the PRA area as a component of the establishment/spread phases.
Additionally, some rusts have resting spore that are resistant to the environment. It is believed that many rust pathogens have been dispersed from country to country as surface contaminants (particularly on clothing of agricultural workers and others).
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