Cause Cronartium ribicola, a fungus that attacks both wild and cultivated species of gooseberry and currant. Black currant (Ribes nigrum) is more susceptible than red currant (R. sativum). Red currant cultivars Viking and Red Dutch are practically immune. The wild species stink currant (R. bracteosum), flowering currant (R. sanguineum), Sierra gooseberry (R. roezli), and Sierra currant (R. nevadense) are very susceptible. The white or five-needled pine is an alternate host for the fungus. Rust of white pine has caused severe losses. Susceptible currants and gooseberries cannot be planted safely nearer than 1000 ft and preferably 0.5 mile from white pine. Ribes and white pines are adapted to disturbance and frequently co-occur in forest and woodland ecosystems.
In spring, spores form in orange pustules (aecia) on tree cankers. Wind distributes aeciospores to currants and gooseberries. Leaves increase in susceptibility as they expand, most susceptible when fully expanded and then decreasing in susceptibility as they age. Uredinia form on the underside of these Ribes hosts and produce urediniospores. The urediniospores can only reinfect more Ribes hosts and continue to do so during the rest of the growing season. Rainfall and long wet periods encourage infection and greater disease development on Ribes. Telia form in late summer where the uredinia are located. The teliospores are not dispersed but germinate to form another spore type called a basidiospore. These spores are blown to white pine, causing new infections. Pycnia appear on the bark the following spring. Aecia erupt from the same area where the pycnia formed the previous year. Aeciospores are produced perennially until the branch dies.
Symptoms On the undersurface of affected currant leaves, small cup-like spots (uredinia) develop. Spots are slightly raised and yellow-orange. Later in the growing season, brownish hair-like structures (telia) develop in the same or new lesions. Defoliation of infected hosts is common as the number of lesions increases.
- Remove white (five-needled) pines within 1000 ft of planting.
- Minimize fertilizer to just what is needed to grow the crop as excessive nitrogen encourages disease development.
- Grow resistant species or cultivars.
Chemical control Apply in the spring when spores are produced on pine.
- Abound at 6 to 15.5 fl oz/A. Do not apply with silicone-based surfactants. May be applied on the day of harvest. Group 11 fungicide. 4-hr reentry.
- Cabrio EG at 14 oz/A. Use before symptoms are anticipated. May be used at harvest. 12-hr reentry.
- Proline 480 SC at 5.7 fl oz/A. Do not use within 7 days of harvest. Group 3 fungicide. 12-hr reentry.
- Propiconazole-based fungicides are registered. Do not use within 30 days of harvest. Group 3 fungicides. 12-hr reentry.
- Bumper 41.8 EC at 6 fl oz/A.
- PropiMax EC at 6 fl oz/A.
- Tilt at 6 fl oz/A.
- Quash at 2.5 oz/A. Do not use within 7 days of harvest. Group 3 fungicide. 12-hr reentry.
- QuiltXcel at 14 to 21 fl oz/A. Do not use within 30 days of harvest. Sprayers should not be used on apples. Group 3 + 11 fungicide. 12-hr reentry.
- Rally 40 WSP at 5 oz/A. Applications may be made up to the day of harvest. Group 3 fungicide. 24-hr reentry.
- Spectracide Immunox at 1.25 fl oz/gal water. May be applied up to the day of harvest. H
References Newcomb, M., Upper, C.D., and Rouse, D.I. 2010. Factors contributing to seasonal fluctuations in rust severity on Ribes missouriense caused by Cronartium ribicola. Phytopathology 100:986-996.
Zambino, P.J. 2010. Biology and pathology of Ribes and their implications for management of white pine blister rust. Forest Pathology, 40:264-291.