Disease

Rust

Details: By NSW DPI

Rust is caused by the fungus Tranzschelia discolour and is identified by brown rust spores on the undersides of leaves. It can be a serious disease in stone fruits.

Disease identification
Rust symptoms can occur on the leaves, shoots and fruits.
The upper surface of the leaf will become speckled with small yellow patches, while the underside develops rusty brown spots
Infected shoots will have small dead patches where the bark splits.
Rust infection on the fruit can be identified by small depressed spots with a dark reddish centre, often with a pale green border.
Damage
Severe rust infection can cause premature leaf fall.
Trees with rust will have considerably reduced yield, with fruit on defoliated trees having reduced sugar levels.
Infected fruit is unsaleable as the infection can penetrate several millimetres into the flesh.
Monitoring
Rust is favoured by warm weather with periods of rain and heavy dews.
Wet periods of 4 hours or more with an optimum temperature range of 13–26C are adequate for spore germination and subsequent leaf infection.
Dry, windy conditions help to spread the rust spores, while rain can splash them onto young leaves.
Carefully monitoring weather conditions and treating orchards in periods that favour disease development is crucial for reducing rust in trees.
Management
Cultural and physical
Good orchard hygiene will moderate the severity of rust infections. Where possible, remove all diseased wood and leaves during pruning and remove all fallen leaves from branches and crotches.
Trees can carry small numbers of green leaves throughout winter. These should be removed and destroyed.
Biological
The are no known biological control agents for the rust pathogen.
Chemical
There are chemical options for controlling rust.