Rust of Faba Bean

Note Number: AG0152
Published: June 2008
Updated: August 2012 

Rust, caused by the pathogen Uromyces viciae-fabae, is a serious disease of faba beans grown in Victoria, New South Wales and South Australia. It can be controlled through the use of resistant varieties and the strategic use of foliar fungicides.

What to look for

On the leaves there are numerous, small, orange-brown pustules, each surrounded by a light yellow halo (Figures 1, 2, 4 & 5). As the disease develops, severely infected leaves wither and may fall from the plant. On stems, the rust pustules are similar, but often larger than those on the leaves. Isolated rust pustules may also appear on the pods. Severe infection may cause premature defoliation, resulting in reduced seed size.

Fig 1. Leaf symptoms of rust pathogen Uromyces viciae-fabae pustules established on leaf of young faba bean plant	Fig 2. Leaf symptoms of teliospores of the rust fungus established on mature faba bean leaf.

Disease Cycle

The rust fungus survives on stubble and self-sown volunteer bean plants. The teliospores produced can infect volunteer bean plants directly without the need for an alternate host (Figure 2). Infection of volunteer faba bean plants is thought to be an important factor in the early development of rust epidemics. Rust spores from stubble and volunteers are blown onto new crops by the wind and infect plants. New spores form in rust pustules on infected plants. Secondary spread of the disease occurs when these spores become air-borne and then spread to other plants (Figure 3).
Rust commonly occurs late in the growing season during podding, resulting in premature leaf drop which can reduce seed weight and size. Humid and warm (more than 20^oC) conditions promote its spread.

	A. The resting stage (telia) survives in a semi-dormant state over summer in crop residues both in the paddock and on seed. B. Teliospores produced on residues are blown by wind and infect volunteer plants and seedlings. C. Aecia are produced on seedlings. D. Aeciospores spread rust within the crop and to other faba bean crops. E. Uridinia are produced on stems and leaves. F. Urdiniospores spread the disease through the crop canopy. G. Telia form on stems and leaves late in the season. H. Disease infested stubble remains after harvest, and some dust and trash is taken with the harvested seed.
Fig 3. Generalised life cycle of rust disease Uromyces viciae-fabae of faba bean. (Source: Bill MacLeod, Department of Agriculture, Western Australia).

Economic Importance

Rust can be prevalent in all areas where beans are grown, and may significantly reduce yields. On its own, the disease has caused yield losses of up to 30%, while in combination with chocolate spot yield reductions of over 50% have been reported (see Chocolate Spot of Faba Bean AG0153). Control measures need to be taken before the disease becomes established in order to minimise crop losses.

Management

Because spores of the fungus can travel long distances to infect a new crop, prevention is difficult.

Paddock selection

A break of at least three years between faba bean crops is recommended. Aim for a separation of 250m from the previous year’s faba bean paddock. Do not sow adjacent to last year’s faba bean stubble.

Variety selection

A number of faba bean varieties are currently available with improved resistance to rust (Table 1).
Table 1. Reaction of faba bean varieties to rust caused by Uromyces viciae-fabae

Chemical control

Foliar fungicides can be used to control the disease and prevent a rust epidemic developing. Crops should be monitored closely if warm (approx 20^oC) temperatures and very high humidity occur. Successful fungicide application relies on crop monitoring and timeliness of application with the right product effective against rust. Several products are registered for use against rust, see Pulse Seed Treatments and Foliar Fungicides or consult your local agronomist

Fig 4. Leaf symptoms of rust on a young faba bean plant.	Fig 5. Rust symptoms on faba bean plant.

Further references

Pulse Australia
Chocolate Spot of Faba Bean (AG0153)
Victorian Winter Crop Summary
Winter Pulse Disorders: The Ute Guide.
Pulse Seed Treatments and Foliar Fungicides

Contact/Services available from DPI

DPI Field Crops Pathology, Grains Innovation Park, 110 Natimuk Rd, Horsham 3400. Tel (03) 5362 2111, or the DPI Customer Service Centre 136 186.

Acknowledgement

This Information Note was originally written by Trevor Bretag and Mary Raynes, June 1998. It was reviewed by Kurt Lindbeck, May 2007 and updated by Helen Richardson June 2008. The current version was reviewed by Helen Richardson and Frank Henry, BioSciences Research - Farm Services Victoria, May 2010. Financial support by the GRDC is gratefully acknowledged.