Thursday, May 26, 2011

Evening Primrose Rust

Evening Primrose (Oenothera species) is a common plant in our semiarid area. These plants like to dry out between waterings but have not had an opportunity to dry out this spring due to our rains and are being infected by a rust fungus as a result.

If you have plants that look like this in your gardens, there is little you can do at this stage. Cutting back the plant and hoping it will recover when weather conditions are less conducive to this fungus problem might help. Controlling this disease with a fungicide in native areas is impractical. In home gardens treating with a topical fungicide can help reduce the spread and severity of this disease.

This rust is most likely Puccinia dioicae. Dendy, et al. (http://www.k-state.edu/pdecology/Solidago2001.pdf) reported a much higher incidence of this disease on goldenrod (Solidago), another host of this fungus, during years of higher levels of precipitation than during normal years.

This heteroecious parasite requires two hosts to complete its life cycle. (An autoecious parasite is one that completes its life cycle on the same host. ) Puccinia dioicae produces aecial spores on members of the following families: Asteraceae, Onagraceae (evening primrose), Phrymaceae, and Valerianceae. It produces teliospores on members of the family Cyperaceae, sedges. To effectively control heteroecious rusts, one could destroy the hosts of one of the stages of rust. In this case removing the sedges in the vicinity of evening primrose would help prevent Puccinia dioicae rust pustules developing on primrose and its other broadleaf flower hosts. How far away the sedges would need to be removed is a good question as these spores spread by wind, rain and by other means.

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