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Brown Leaf Spot and Root Rot of Lupins

Note Number: AG0120
Published: June 2006
Updated: February 2013

The most important diseases of lupins in Victoria are brown leaf spot and root rot, which are both caused by the fungus Pleiochaeta setosa. Control measures are required to protect the roots and foliage before the disease becomes established in order to minimise crop losses.

What to look for

Pleiochaeta setosa can infect all plant parts, but is usually first seen on the leaves. Leaf, pod and stem infections begin as small, dark brown spots which enlarge to form black networks on leaves, and extensive brown areas on pods and stems (Figure 1). When leaves are severely infected they die and drop off. Infection up to the four leaf stage can kill seedlings. When pods are heavily infected the fungus may infect the developing seed.

The brown leaf spot fungus may also infect lupins on the upper taproot (Figure 2). This infection appears as a dark brown lesion and may cause the plant to die, especially when the soil is waterlogged just after sowing. Other root rotting fungi such as Rhizoctonia and Fusarium species are frequently associated with brown leaf spot infections at the base of the stem.

Economic Importance

Pleiochaeta setosa is prevalent in all areas where lupins are grown. Lupin plants may be infected at any stage of growth. Under Victorian conditions Pleiochaeta root rot can reduce establishment, while brown leaf spot is most important from emergence until rapid growth starts in early spring. Later, as lupins approach maturity and are growing rapidly, loss of some lower leaves from the disease is of little consequence.

Disease Cycle

During the growing season large numbers of spores are produced when diseased leaves fall onto the soil surface. These spores start new infections when they are splashed onto foliage by rain. 

The pathogen is carried over from one season to the next on previously infected plant material, in infested seed or as spores on the soil surface. At the start of the next cropping season, spores that survived the summer may become incorporated into the soil with tillage or sowing operations.

When the next lupin crop is sown, soil-borne spores germinate and infect the roots of lupin seedlings. Spores that have survived on the soil surface are splashed upwards by rain droplets, and infect leaves and stem.

Seed-borne infections are important for dissemination of the pathogen over long distances, and are responsible for initial infection in clean paddocks that are isolated from other lupin crops. Severely affected pods can contaminate seed lots and act as a source of infection after sowing. Once infection is established within the crop, secondary infection of other plant parts can occur by splash dispersal of fungal spores during rain.

Management

Brown leaf spot and root rot can be effectively controlled when an integrated approach to disease management is implemented.  This involves using a number of strategies including crop rotations, seed dressings, resistant cultivars, and retaining cereal stubble. 

Crop rotation is an important management strategy as the number of Pleiochaeta spores in the soil is reduced by half, every year a non-lupin crop or pasture is grown in the rotation. The only other known host for brown leaf spot is seradella, a low-yielding legume which is not common in Victorian lupin areas. Sowing lupins into cereal stubble will reduce rain splash of spores onto lupin plants. 

Another important method for controlling brown leaf spot is to apply a seed dressing, although this only suppresses the disease and does not provide complete control.

Registered seed treatments containing either iprodione or procymidone will reduce the transfer of the disease to the seedling, and can reduce leaf drop by 50 per cent.

Variety selection is also an important management strategy. New narrow leaf lupin varieties (Lupinus angustifolius) have been released with resistance to Pleiochaeta root rot and brown leaf spot. Broad leaf lupin (Lupinus albus) varieties are available with tolerance to brown leaf spot, but can be susceptible to root rots under wet conditions, and so are limited to well-drained soils. Long rotations are important so that lupin stubble will be decomposed before the next lupin crop is sown.

Recommendations for control of brown leaf spot:

• Develop long crop rotations and avoid planting lupins in paddocks adjacent to lupin stubble
• Sow into a cereal stubble to reduce the amount of rain splashed spores.
• Treat all seed with a recommended fungicide and ensure that seed lots are free from plant debris
• Use resistant cultivars.

Further references

More detailed information can be obtained from the DPI Information Note Series: www.dpi.vic.gov.au/graindiseases

Pulse Australia
Victorian Winter Crop Summary
Seed Health Testing in Pulse Crops (AG1250)
Pulse Seed Treatments and Foliar Fungicides
Brown spot and root rot of lupins. Farmnote 5/96

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

Acknowledgements

This Agnote was developed by Mary Raynes and Helen Richardson July 2006. It was reviewed by Helen Richardson, BioSciences Research and Frank Henry, Farm Services Victoria – February 2013. Financial support by the GRDC is gratefully acknowledged.