Act now to minimise threat of infection

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

Controlling rust diseases in cereals requires an ongoing commitment by growers to stick with resistant cultivars, and to control the diseases both during and between cropping cycles with chemicals or grazing if necessary.

The good news is that action taken prior to sowing in 2004 will not only reduce the risk of rust infection this season, but it will also make a significant contribution to rust control in 2005 with further benefits in subsequent seasons.

The table shows things that growers should be doing during the late summer/ autumn lead-up to this year’s cropping cycle to minimise the risk of rust infection in 2004.

The fungal pathogens that cause rust diseases can only survive for extended periods on living host tissue. Fortunately, agronomic practices like minimum tillage that retain dead stubble have little effect on the survival of rusts from one season to the next.

During the non-cropping period in late summer/early autumn, cereal rust populations crash because of the unavailability of living host tissue.

However, self-sown or volunteer cereals that establish during the break between cropping cycles can harbour rust diseases and allow the pathogens to invade early with potential for substantial epidemic development.

It is therefore important that growers monitor their fields, particularly following rainfall events on stubbles that grew susceptible varieties in 2003, and destroy any volunteer cereals either by grazing, slashing, cultivation or with herbicides.

Resistant varieties = resistant crops + resistant volunteers! The added advantage of growing resistant varieties is that any self-sown cereals derived from them will have the inbuilt resistance and reduce the amount of rust surviving from one year to the next.

Experiences in 2003 have indicated that several current varieties are particularly vulnerable to rust infection, including the wheat variety H45Variety protected under the Plant Breeders Rights Act 1994. (stripe rust), and the barley varieties BaudinVariety protected under the Plant Breeders Rights Act 1994., HamelinVariety protected under the Plant Breeders Rights Act 1994. and KeelVariety protected under the Plant Breeders Rights Act 1994. (leaf rust).

For both crops there are fortunately alternative varieties to these in most cases. In contrast, oat growers have very few options when it comes to rust resistant varieties because all current varieties are susceptible to stem rust, and only the newly released Volta is resistant to leaf rust.

Where possible, susceptible varieties should be avoided and if grown, they will require careful monitoring and may need to be treated with fungicide if rust develops.

Treating seed with fungicide is important if there is concern about significant oversummering inoculum, or where late-sown crops are being seeded in areas vulnerable to disease.

Triadimenol ($50-$75 per tonne wheat) and triticonazole ($70-$140) seed dressings, while cheaper, provide protection to seedlings only, while more expensive treatments like fluquinconazole ($320) and fertiliser applied flutriafol ($120-$250) provide longer protection. Several points must be considered:

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