Bean rust (Phaseolus spp.)
Uromyces appendiculatus var. appendiculatus. Previously Uromyces phaseoli.
Worldwide; Asia, Africa, North, South and Central America, the Caribbean, Europe, Oceania. It is recorded from American Samoa, Australia, Fiji, Guam, New Caledonia, New Zealand, Papua New Guinea, and Solomon Islands. However, according to the check list for Solomon Islands (McKenzie and Jackson, 1986) it is probable that the two records of Uromyces appendicatus on cowpea in Solomon Islands are misidentifications of Uromyces vignae.
Mainly on beans, Phaseolus species. Another rust, Uromyces vignae occurs on Vigna species (Vigna marina and Vigna unguiculata ssp. sesquipedalis). This rust occurs widely, and is present in Fiji, Samoa, Solomon Island, and Tonga.
Circular pustules, 1-2 mm diameter, light green with distinctive yellow haloes on the top surface, scattered over both sides of the leaves, and on the pods (Photos 1&2). Later, the pustules rupture producing reddish-brown powdery spore masses.
The rust has all five spore stages, and completes its life cycle on Phaseolus species. This is in contrast to other rust species that have fewer life stages, and others that may have all stages, but more than one host.
Spread is by spores blown in the wind. Some spore types are specially adapted for survival and have thick dark walls; they can survive a long time in the atmosphere, travelling great distances. The hardiness of the spores increases the chance infection of bean crops. In the tropics, new bean crops often overlap old ones, so that survival of rust is more easily assured
The rust causes a destructive disease of beans. Loss in yield are reported from many countries; not only do the losses depend on the environment - the rust favours relatively cool, damp weather with heavy dews - but also on variety as there are differences in susceptibility.
Look for reddish-brown circular pustules with yellow halos, producing masses of spores on leaves and pods. Expert examination is necessary to distinguish between Uromyces appendiculatus and Uromyces vignae.
There are several ways to reduce the impact of rust on Phaseolus beans, apart from using fungicides:
There are a number of varieties with resistance to bean rust; contact agriculture authorities or seed suppliers to see if any are available in your area.
If fungicides are needed, use manacozeb. Start to spray when symptoms first appear.
AUTHOR Grahame Jackson
Photos 1 Kohler F, Pellegrin F, Jackson G, McKenzie E (1997) Diseases of cultivated crops in Pacific Island countries. South Pacific Commission. Pirie Printers Pty Limited, Canberra, Australia. Information from Diseases of vegetable crops in Australia (2010). Editors, Denis Persley, Tony Cooke, Susan House. CSIRO Publishing.
Produced with support from the Australian Centre for International Agricultural Research under project PC/2010/090: Strengthening integrated crop management research in the Pacific Islands in support of sustainable intensification of high-value crop production, implemented by the University of Queensland and the Secretariat of the Pacific Community.
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