by Rhonda C. Koski & C. C. Powell
Department of Plant Pathology
The Ohio State University
(Condensed from an article in Ohio Florists’ Association Bulletin, August 1985)
Rust disease of fuchsia has become increasingly prevalent and damaging in Ohio greenhouses as well as in other states in recent years. Management of the disease requires and understanding of the biology of the pathogen, its diagnosis, and life cycle. Thus, the following literature review and management guide has been compiled.
According to Gaeumann (1944) fuchsia rust was first described in New Zealand and, a bit later, from Guatemala. Through the 1930’s, the disease was considered tropical, limited to greenhouse climates in temperate regions of the world. Gaeumann, noting its occurrence outdoors along the West coast of England, questioned the relationship of the fuchsia rust fungus to those rusts found on weeds growing in similar temperate areas.
His inoculation studies proved that the pathogen (disease-causing organism) on fuchsia was Pucciniastrum eqilobii, the same fungus that cause rust on species on Epilobium and Clarkia.
Since the 1960’s, reports of this disease have been published in the United States from the West coast, Ohio, North Carolina, Connecticut, Hawaii, and Pennsylvania.
In New Zealand, this rust has been found on horticultural hybrids of Fuchsia growing both outdoors and under glass.
The disease has been found on Fuchsia growing in greenhouses and occasionally on those growing out-of-doors in areas all along the West Cost. In 1978, Strider and Jones reported the first occurrence of the rust in North Carolina occurring on Fuchsia plants growing in a plastic greenhouse in the western part of the state. At that time, 25 cultivars of Fuchsia were being propagated. None of the cultivars escaped infection; many were severely damaged, and some were killed by this disease. Gardner first reported fuchsia rust occurring in Hawaii in 1979.
Bushes of Fuchsia hybrida and Fuchsia magellanica which had become naturalized in the Hawaii Volcanoes National Park were severely infected with this disease.
Schroeder and Judd report of losses up to 100 percent occurring in Connecticut greenhouses. They noted that the most serious losses occurred during propagation, where the close spacing of plants under mist with little air movement favors rapid development of this disease.
The Characteristic symptoms of fuchsia rust include large, circular, yellow spots on the upper surface of an infected leaf. These spots are often surrounded with a reddish-purple border. The under side of the leaf reveals masses of orangish-yellow rust pustules, which are the uredia (a fruiting body) which contain urediospores. Urediospores can also be seen on upper leaf surfaces as the lesions age. These Urediospores are able to incite new infections on the leaves of the same plant as well as on the leaves of other, nearby Fuchsia plants. Infected leaves are weakened and defoliate prematurely. This defoliating will seriously weaken the plants. If control measures are not initiated, the plants can be completely defoliated and killed by this disease.
Life Cycle of the Pathogen
Only the redial stage is involved in fuchsia rust on Fuchsia. The telial or overwintering stage has not been observed on Fuchsia. Telial production has been observed on species of Epilobium Van Sickle (1973), and Strider and Jones (1978) indicate the E. anqustifolium, Fireweed serves as a host for the uredial stage of this disease. Fireweed is extremely common in open forests, abandoned pastures, and along roadsides of the Pacific Northwest and the Rocky Mountain states. Thus, the association of the disease with the weed host is of particular concern to West coast growers. Many Ohio greenhouse growers obtain their Fuchsia in the autumn as “dormant” plants from the western states of California and Oregon. We speculate the invisible infections could, at times, be present in the buds or on the small leaves, sometimes seen alive on the plants. In addition, Ohio growers that hold over infected Fuchsia from one year to another or that retrieve cuttings from landscape plants in the fall could also introduce the disease into the succeeding or future crop. In hot weather the pathogen is not obviously active, but may be present in invisible infections. After entering the greenhouses of Ohio, the pathogen becomes active as the plants break dormancy and the weather cools. The disease can spread rapidly from plant to plant, as long as Fuchsia plants are present. It is especially epidemic when such plants are being irrigated overhead and water splashes from leaf to leaf.
The control of fuchsia rust is based upon an integrated approach, employing cultural practices, chemicals, as well as the use of resistant cultivars. Cultural control measures include the removal of infected leaves as they appear, disposal of severely infected plants, wider spacing of the plants to facilitate faster drying of the foliage, avoidance of overhead irrigation, ventilation to reduce the relative humidity in the greenhouse, and the elimination of any Epilobium species which are know to be growing near the greenhouse. There does appear to be cultivar differences as to susceptibility of Fuchsia to fuchsia rust. (I’ve observed ‘Texas Longhorn’ and ‘Barbara’ [Tolley] to be among the most susceptible cultivars –C.H.) Because of the highly infectious nature of the pathogen, it is doubtful as to how practical such cultural practices are in completely managing fuchsia rust in a commercial greenhouse. Protective chemical sprays will probably be necessary. There are chemicals available which will control fuchsia rust in greenhouses. However, there are very few chemicals for which control of fuchsia rust is listed on the label.
From AFS Bulletin of October 1987.