The new pathotype of leaf rust has recently been found in one volunteer crop of Marombi wheat near Coonabarabran.

This pathotype caused large losses on Marombi crops in the north of the state last year.

The new leaf rust pathotype was first detected in WA in 2002 and has since spread across the country.

The popular dual purpose variety, Marombi, is highly susceptible to a new race of leaf rust.

The leaf rust pathotype has the potential to severely damage any Marombi crops that are allowed to go through to grain this season.

All three wheat rusts, stripe rust, leaf rust and stem rust have similar life cycles needing a green bridge to survive over the summer period.

In the north of the state, where there was summer rainfall, there were sufficient volunteer plants for rust survival.

Leaf rust, like other rust spores, is wind-blown.

It is then likely to spread across the NSW wheat belt to establish rust in newly emerging susceptible wheats.

What differs is the optimum temperature for growth of these rusts.

The optimum temperature for stripe rust is 8-15 C.

The optimum temperature for leaf rust is much warmer, 15-22 C.

Therefore we are likely to see leaf rust developing later in the season with the levels not detectable until the weather warms.

The leaf rust in Marombi is caused by a new race or mutation.

There are also two other pathotypes of leaf rust that have been found, one that is virulent on Mackellar and the other on Rudd.

Both of these pathotypes were likely introduced from overseas.

Leaf rust spores will be much more orange-brown in colour than stripe rust and also differ from stripe rust in that leaf rust spores do not form stripes on the leaf surface in older plants.

Growing resistant varieties is the best option to avoid rust.

Like other rusts, leaf rust can be controlled by fungicides, but it is important to control the infection early to minimise yield loss.

Where one spray is to be used, optimum timing may be at flag leaf emergence.

If infection is severe, two sprays maybe required.

It is important to monitor any crops for signs of the disease.

If you are unsure, plant samples can be tested free of charge.

Please report any sightings of rust in your area to your district agronomist.

Samples will be forwarded to the national rust survey.

Also report any sightings of rust on varieties that you would expect to be resistant.