Stripe rust

 

Stripe rust often appears first on older leaves with small and round yellow-orange pustules, which are raised and are easily wiped off. As wheat reaches maturity black spores can form, which can infect upper leaf surfaces, leaf sheaths, awns and inside the glumes. Like other rusts, stripe rust can easily be seen from afar in patches known as ‘hot spots’ of infection. Sometimes confused with leaf rust, stripe rust is easiest to identify early in the morning when new spores have formed. As the day goes on pustule colours tend to fade, making identification more difficult. 

 

The presence of green host plants over summer allows stripe rust to survive all year, particularly   volunteer wheat plants which offer a ‘green bridge’ for stripe rust to survive on. Due to high temperatures during summer only small amounts of stripe rust can survive. Importantly, all it takes is one infected leaf per 30 ha of re-growth to facilitate an outbreak of stripe rust. Stripe rust is readily spread by wind; spores become airborne, landing on wheat plants and infecting the plant. Successful infection requires high humidity, temperatures of less than 18 °C (ideal range 6 – 12 °C) and a minimum of three hours of leaf wetness. Once infected, the fungus can withstand short periods of high temperatures (> 40 °C). During conditions of low humidity spores can travel long distances, this often results in uniform patterns of development rather than hot spots of infection during mid-spring.  

Stripe rust can be managed effectively by implementing a range of tactics. It is vital to control the green bridge over summer to reduce inoculum levels by removing or destroying volunteer wheat plants and other host species, particularly in the six weeks prior to sowing. Avoid planting susceptible or very susceptible varieties of wheat, rather select varieties with more resistance that also meet agronomic and quality standards.

 

The decision to provide early protection from stripe rust with seed dressings, fertiliser fungicide treatments or waiting to apply foliar fungicides in-crop, will differ from region to region and farm to farm. Factors to consider are; the presence of a green bridge and therefore potential for stripe rust carry over, variety selection and the capacity to be able to spray a whole program in a timely manner. 

 

Seed and fertiliser fungicide treatments play an important role in controlling stripe rust by protecting young seedlings. Some seed treatments can reduce coleoptile length, which needs to be considered at sowing. Treatments applied to fertiliser often don’t control smuts and bunts, therefore additional seed dressings may be required. Jockey® Stayer®  is registered for the control of stripe rust in wheat for up to six weeks (at the 4.5 L/t rate) and suppression thereafter. 

 

Crops should be monitored during the growing season and if an outbreak of stripe rust occurs apply a registered fungicide. Aviator® Xpro® and Prosaro® are both protective and curative fungicides, unlike some other fungicides which only offer protective properties against stripe rust. They are both registered for the control of stripe rust in wheat. Consult CropLife Fungicide Resistance Management Strategies as a guide to the responsible use of fungicides and always follow the product label for specific use instructions.

Beard, C, Thomas, G and Jayasena, K (2018), ‘Managing stripe rust and leaf rust in Western Australia’, Department of Primary Industries and Regional Development (DPIRD), https://www.agric.wa.gov.au/grains-research-development/managing-stripe-rust-and-leaf-rust-wheat-western-australia