Wet or dry, rust surprises

Photo of green bridge plant

By Professor Robert F. Park and Dr Colin R. Wellings (Dr Wellings is on secondment from NSW Primary Industries), University of Sydney Plant Breeding Institute, Cobbitty

Rust diseases like damp conditions; it is often said that "good cropping years are good rust years". Conditions during the summer preceding a cropping period can also be important in determining the potential for a rusty year.

The 2005 cropping season began with dry conditions in most of eastern Australia and wetter conditions in the west. The expectation could therefore be for rust in the west and little rust in the east. Oddly, several recordings of stripe rust and leaf rust have already been made in the east, but there have been no reports of rust in WA to date.

The first confirmed sample of wheat stripe rust in 2005 was collected from a Whistler crop at Tarcutta (60 kilometres east of Wagga Wagga in the south-western slopes of NSW) in the last week of May. This represents a very early report of stripe rust for the 2005 winter crop season.

In comparison, the first confirmed report in 2004 was collected from a Diamondbird crop in early August. This crop was considered to have become infected from a nearby Whistler field that was sown much earlier in 2004.

The Tarcutta field of Whistler was sown on February rain, and was intended for early grazing. The extent of early sowings of Whistler is unclear, but we presume that those that were established in February and have survived the dry autumn period may be potential sources of inoculum for main season plantings.

Two further reports of stripe rust from eastern Australia were received in late June, the first of which came from Grenfell (southern NSW) on the variety WylahPBR. Infection hot spots were evident in the field. The crop was sown on "a fluke storm" in late April. The second report, yet to be confirmed, was from a trial site at Cowra on the variety EGA GregoryPBR, sown in early April.

Although early crops are relatively rare in the east in 2005, these sightings should give cause to monitor carefully those crops that have established well.

Late plantings will likely predominate in the east and, depending on the levels of rust development in early planted fields, may come under pressure in late winter or early spring. However, with just two confirmed stripe rust samples to date, it is far too early to predict epidemic development.

Leaf rust samples were received from Cooma (Monaro region of southern NSW) on 18 May. The varieties were TennantPBR and MackellarPBR, which are both long-season winter wheats suitable for grazing and grain recovery.

In contrast, the first leaf rust samples in 2004 were received in early August. The pathotype of rust responsible was first detected from MackellarPBR wheat in October 2004, and appears to be new. Work is under way to characterise this pathotype in more detail.

This alert should serve to remind cooperators to be aware of the possibility of rust infections in commercial fields, and to be actively looking for signs of infection.

Cereal rust samples should be collected when leaves are dry and showing evidence of rust infection. Several leaves can be posted in a paper envelope (no plastic wrapping), including variety details (if known), location of the sample and contact details for correspondence. Samples can be posted to:

Australian Cereal Rust Survey
Plant Breeding Institute
Private Bag 11
Camden NSW 2570

Package offer on Cereal Leaf and Stem Diseases, Ground Cover Direct, page 31

[Photo: Conditions during the summer can influence rust development because rust diseases can only survive on living plants. Wet summers favour the development of self-sown cereals (volunteers: the green bridge, above) that can allow rust pathogens to carry over from one season to the next.]

PBR Varieties displaying this symbol beside them are protected under the Plant Breeders Rights Act 1994.