Fuchsia rust is caused by the fungus Pucciniastrum epilobii. The disease occurs throughout the United States and is common in Massachusetts, particularly during the winter months. The most serious losses occur during propagation; however, diseased plants at any stage of growth are unmarketable. Potted plants may recover from this disease but defoliation significantly weakens the plants and occasionally results in death.
The disease is first recognized when large circular areas of chlorosis appear on the upper surface of the leaves. On the underside, masses of yellow-orange urediospores are produced. As the disease becomes severe, the spores appear on both sides of the leaves and the circular spots become less distinct. Occasionally, the spores form along the veins. Affected leaves may be deformed and defoliation commonly occurs.
Rust fungi are highly specialized parasites that are dependent on living plants for growth and development. Most have complex life cycles that include up to five different spore stages and two different hosts to complete their life cycle. Pucciniastrum epilobii, the cause of Fuchsia rust, requires both Abies (fir) and Epilobium (fireweed) to complete its lifecycle. Fuchsia is related to fireweed and is also a host of the fungus. The life cycle is as follows. Teliospores, which allow the fungus to survive the winter, form on infected fireweed in autumn (teliospores have not been reported on fuchsia). In the spring, the teliospores germinate and produce basidiospores which infect the needles of various species of fir (in our region, white and balsam fir). Sexual conjugation of the fungus occurs on the fir needles followed by the development and release of aeciospores. The aeciospores can only infect fireweed, and perhaps fuchsia, but cannot reinfect fir. The fungus then produces urediospores on infected fireweed and fuchsia. The rusty appearing blisters on the foliage contain masses of these urediospores. The urediospores reinfect fireweed and fuchsia repeatedly, but cannot infect fir. The fungus can reside in the greenhouse, spread, and reinfect fuchsia as long as infected fuchsia or fireweed are present.
The initial source of spores may be from fireweed or fir. Stock kept outdoors during the summer may become infected by air-borne spores. Stock plants brought in from elsewhere may also be a source of the disease.
Eliminate fireweed in the vicinity of the greenhouse. Fuchsias that have rust should be discarded or isolated from healthy fuchsias. Diseased plants can be cut back to the wood, thus reducing the inoculum in the greenhouse. When plants begin to develop new foliage, it will be free of rust but a protective fungicide should be applied. Plants should be spaced to provide good air circulation. Avoid wetting the foliage during watering.
Fungicides: Many fungicides are registered to control rust diseases on ornamentals. Few of these materials list Fuchsias on their label and should be tested before applying to the entire crop. Dithane (mancozeb), Exotherm Termil (chlorothalonil), and Medallion (fludioxonil) do list Fuchsia on their labels. The following table is a selection of some commonly used fungicides for control of Rust diseases.
|Common Name||Trade Name||Rate/100 gal||Comments|
|azoxystrobin||Heritage||1-4 oz||Broad crop clearance. Apply as a preventative|
|chlorothalonil||Daconil, Echo, Manicure||5.5 fl oz||Broad crop clearance. Avoid applications during bloom.|
|kresoxim-methyl||Cygnus||3.2-6.4 oz||Broad crop clearance.|
|mancozeb||Protect, Dithane, Fore||See label||Broad crop clearance.|
|myclopbutanil||Eagle||6-12 fl oz.||Test on plants not listed on label.|
|thiophanate-methyl||Cleary's 3336||12-16 oz||Broad crop clearance.|
|triadimefon||Strike||2-4 oz||Test on plants not listed on label.|
|triflumizole||Terraguard||4-8 oz||Do not use on Impatiens.|
The addition of an adjuvant such as Triton B-1956® to the fungicide will improve performance. Begin spraying at the first sign of disease and repeat at 7 to 10 day intervals. Dithane M-45® is compatible with most commonly used agricultural fungicides, insecticides and growth regulators. Consult a spray compatibility chart for specific combinations.Prepared by Dr. Robert L. Wick, Department of Plant, Soil and Insect Sciences, Fernald Hall, Room 111, University of Massachusetts Amherst, MA 01003. Tel. (413) 545-1045 Fax (413) 545-2532.
Revised 11/10 by M.B. Dicklow
UMass Extension Plant Diagnostic Laboratory